When Is Corporation Tax Due? UK Deadlines, Rates and Penalties 2026/27

Last updated: May 2026.

If you run a UK limited company, the corporation tax deadline is one of the few dates you genuinely cannot afford to get wrong. Unlike VAT or PAYE, corporation tax has an unusual quirk: you have to pay before you file. The payment falls due nine months and one day after your accounting period ends, but the CT600 return is not due for a further three months. Directors who assume the two dates are the same routinely pay late without realising it.

This guide is the definitive reference for UK corporation tax deadlines in the 2026/27 tax year. It covers the payment and filing dates, how to work them out from any year-end, the rules for large companies that pay by instalments, every penalty and interest charge HMRC applies, what to do if you cannot pay, and the special cases that catch out new and closing companies. Worked examples use real pound amounts throughout.

What is the corporation tax payment deadline?

The single most important rule: corporation tax is due 9 months and 1 day after the end of your accounting period.

If your company's accounting period ends on 31 March 2026, your corporation tax payment is due by 1 January 2027. If it ends on 31 December 2025, payment is due by 1 October 2026.

This nine-month-and-one-day rule applies to the vast majority of UK limited companies — anyone with taxable profits below £1.5 million. Larger companies pay in quarterly instalments instead, which we cover in detail further down.

The "and 1 day" matters. It is not a rounding error. A company with a 31 March year-end does not pay on 31 December; it pays on 1 January. HMRC sets the date this way deliberately, and your payment reference and online account will both show the precise due date.

Key corporation tax dates at a glance

Why you pay corporation tax before you file the return

This is the part that surprises most first-time directors. The payment deadline (9 months and 1 day) arrives three months before the filing deadline (12 months). You are expected to pay corporation tax based on your own calculation, then submit the formal CT600 return afterwards.

For a 31 March 2026 year-end:

• 1 January 2027 — corporation tax payment due
• 31 March 2027 — CT600 return and accounts due

In practice this means your accounts and tax computation need to be substantially complete by the payment deadline, even though you have longer to formally file. You cannot wait for the 12-month filing date to work out what you owe. Either finish your accounts early, or pay a reasonable estimate by the payment deadline and adjust later.

HMRC does not penalise you for paying an estimate that later proves slightly too high or too low. Overpayments are refunded with interest; small underpayments simply attract interest on the shortfall. What HMRC does penalise is paying nothing, or paying obviously too little, by the nine-month-and-one-day date.

How to work out your deadline from any year-end

Every corporation tax deadline is calculated from the last day of your accounting period. Here is the full 2026/27 reference table — find your year-end month and read across.

The two most common year-ends in the UK are 31 March (it aligns roughly with the tax year) and 31 December (the calendar year). Companies often default to the anniversary of incorporation in their first year, then keep it or change it later.

A note on weekends and bank holidays

The legal deadline does not move if it falls on a weekend or bank holiday — but the practical consequences do. If your payment deadline is a Saturday, your money still has to reach HMRC's account by that date. Faster Payments and CHAPS clear quickly, but Bacs and cheques do not. Always allow at least three working days for the payment to clear, and pay earlier if the deadline lands near a weekend or the Christmas period. We return to payment timing below.

Corporation tax deadlines vs your other company filing dates

Corporation tax is only one of several recurring deadlines a UK company has, and they are easy to confuse because some sound similar and fall near each other. The most common mix-up is between the corporation tax payment (to HMRC) and the statutory accounts filing (to Companies House) — both fall around the nine-month mark, but they are different obligations, sent to different bodies, with different penalty regimes.

Here is how a typical company's annual deadlines line up for a 31 March 2026 year-end:

Two practical points follow from this table. First, your accounts go to Companies House one day before your corporation tax is due to HMRC — so in practice your numbers must be finalised by late month nine regardless. Second, late accounts at Companies House carry their own separate penalties (starting at £150 for a private company up to a month late and rising to £1,500 for more than six months), entirely independent of HMRC's CT600 penalties. Missing month nine can therefore cost you twice. Our annual accounts filing guide covers the Companies House side in full.

The takeaway: treat the nine-month mark as the real deadline for getting your year-end work done. Everything else — the extra day for payment, the extra three months for the CT600 — is breathing room you should not rely on.

Registering for corporation tax

Before any deadline applies, your company has to be registered for corporation tax. When you incorporate through Companies House, HMRC is notified automatically and sets up a corporation tax record. But registration is not complete until you tell HMRC the company has started to trade (become "active").

You must do this within 3 months of starting business activity. Starting to trade includes buying or selling, advertising, employing someone, renting premises, or earning interest — not just invoicing customers. You register through your company's HMRC online account using the company's Unique Taxpayer Reference (UTR), which arrives by post a week or two after incorporation.

A company that never trades is dormant for corporation tax and does not have a payment or filing obligation for that period, though it still files dormant accounts with Companies House. If a dormant company later becomes active, the three-month registration clock starts from that point.

Understanding your accounting period

Your accounting period is the period your corporation tax is calculated for. It is usually the same as the financial year covered by your statutory accounts — normally 12 months — but the two are not always identical, and the differences cause real problems for new companies.

Key rules:

• A corporation tax accounting period can be up to 12 months long but never longer.
• It normally starts the day after the previous period ends.
• It ends on your accounting reference date (your chosen year-end) — or earlier if the company stops trading.

The first-period trap: when one set of accounts becomes two returns

A brand-new company's first set of statutory accounts often covers more than 12 months — typically the period from incorporation to the first accounting reference date, which Companies House sets as the end of the month of the first anniversary. So a company incorporated on 10 June 2025 has a first accounting reference date of 30 June 2026 — a period of 12 months and 20 days.

For corporation tax, that single long period must be split into two accounting periods:

1. The first 12 months (10 June 2025 to 9 June 2026)
2. The remaining days (10 June 2026 to 30 June 2026)

That means two CT600 returns and two separate payment deadlines, even though Companies House only wants one set of accounts. Each return has its own nine-months-and-one-day payment date and its own twelve-month filing date. This catches out a large share of first-year directors. If your first accounts cover more than 12 months, expect two corporation tax returns.

Changing your year-end

You can change your accounting reference date with Companies House. Shortening a period is straightforward and can be done as often as you like. Lengthening it is limited (generally once every five years, and never beyond 18 months). A change to your year-end changes every downstream corporation tax deadline, so update your reminders the moment it is confirmed. Our company year-end checklist walks through the practical steps.

Corporation tax rates for 2026/27

The amount you owe by the deadline depends on the rates in force for your accounting period. The UK runs a tiered system.

Marginal relief in the £50,000–£250,000 band

If your profits fall between the lower and upper limits, you pay the main 25% rate but then deduct marginal relief, which tapers the effective rate. The marginal relief fraction for 2026/27 is 3/200. The practical effect is a smoothly rising effective rate:

The marginal band carries a high marginal rate of 26.5% on each extra pound earned between £50,000 and £250,000 — higher than the headline 25%. That makes timing of income and deductions around year-end genuinely worth planning. For full worked examples of the marginal relief formula, see our corporation tax rates and thresholds guide, or run your own figures through the corporation tax calculator.

Associated companies reduce your thresholds

The £50,000 and £250,000 limits are divided by the number of associated companies plus one. If you control two companies, each has a lower limit of £25,000 and an upper limit of £125,000. This pushes smaller companies into the marginal band — or even the main rate — sooner than their profits alone would suggest. It is one of the most overlooked features of the system for directors who run more than one company.

Quarterly instalment payments for large companies

Companies with sizeable profits do not get the nine-month-and-one-day rule. Instead they pay corporation tax in quarterly instalments, some of which fall due before the accounting period has even ended.

Large companies (£1.5m–£20m profits)

A company is "large" if its profits exceed £1.5 million (divided by associated companies plus one). Large companies pay in four instalments. For a 12-month accounting period the instalments are due on the 14th day of months 7, 10, 13 and 16, measured from the start of the period.

For an accounting period running 1 April 2026 to 31 March 2027:

Each instalment is normally a quarter of the estimated total liability for the year — so large companies have to forecast their corporation tax during the year and revise as they go.

There is a one-year grace period: a company is not treated as large if its profits are £10 million or less (reduced for associated companies) and it was not large in the previous year. This stops a single good year from immediately forcing a company onto instalments.

Very large companies (over £20m profits)

Companies with profits over £20 million pay even earlier. Their four instalments fall on the 14th day of months 3, 6, 9 and 12 from the start of the accounting period — so the entire year's tax is paid before the period ends.

Worked example: instalments for a large company

A company with a 1 April 2026 to 31 March 2027 accounting period expects taxable profits of £4 million and an estimated corporation tax liability of £1,000,000. As a large company it pays in four instalments of roughly £250,000 each:

If, by the third instalment, the company revises its profit forecast upward, the later instalments are increased so the full liability is covered — and HMRC charges interest on any earlier instalment that, with hindsight, was underpaid. Conversely, if profits fall, the company can reduce or even reclaim instalments. This is why large companies need a reliable in-year tax estimate, not just a year-end calculation.

Instalment payments must be made electronically

All instalment payments must be made by electronic means. Missing an instalment, or underpaying one, attracts interest from the instalment due date — and HMRC charges a lower "instalment" interest rate while the period is open, switching to the standard late-payment rate afterwards.

How to pay corporation tax

You cannot pay corporation tax by post any more — there is no payslip and HMRC does not accept cheques through the letterbox for it in the way it once did. The accepted methods are:

• Online or telephone banking (Faster Payments — usually same day or next day)
• CHAPS (same working day if sent before your bank's cut-off)
• Bacs (allow three working days)
• Direct Debit through your HMRC online account (allow five working days the first time you set one up, three thereafter)
• Debit card or corporate credit card online (a non-refundable fee applies to corporate credit cards; personal credit cards are not accepted)

Your 17-character payment reference

Every corporation tax payment needs the correct 17-character payment reference — not your UTR on its own. The reference is your 10-digit UTR followed by the letter "A", then four digits identifying the accounting period, then "08" or similar. Crucially, the reference changes for each accounting period. Using last year's reference is one of the most common reasons a payment is recorded against the wrong period and a company is wrongly chased for arrears. You will find the correct reference for the current period in your HMRC online account or on the notice to deliver a return.

Pay early — the deadline is the cleared funds date

The deadline is the date the money must reach HMRC, not the date you send it. If your deadline is 1 January and you set up a Bacs payment on 30 December, it will arrive late. Treat the official deadline as a "cleared by" date and send funds at least three working days earlier — more around bank holidays. There is no penalty, interest cost, or downside to paying weeks early; HMRC simply holds the credit against the period.

Penalties for late payment of corporation tax

Here is an important distinction: there is no fixed penalty for paying corporation tax late. Late filing triggers fixed penalties; late payment triggers interest instead.

Late payment interest

Interest accrues daily from the day after the payment deadline until the tax is paid. HMRC's late payment interest rate is set at the Bank of England base rate plus 4 percentage points (the margin rose from 2.5 to 4 points in April 2025). With the base rate in 2026 sitting around 4.5%, that puts the late payment interest rate at roughly 8.5% per year.

Interest is not optional and HMRC does not waive it for honest mistakes — it is treated as commercial restitution for late use of public money, not a punishment. It is, however, a tax-deductible expense for the company.

Worked example: interest on a late payment

A company owes £10,000 in corporation tax and pays it 90 days late at an 8.5% annual rate:

• Daily rate: 8.5% ÷ 365 = 0.0233%
• Daily interest: £10,000 × 0.0233% = £2.33
• 90 days: £2.33 × 90 = £209.70 in interest

On a larger bill the numbers escalate. A £60,000 liability paid 120 days late at 8.5%:

• Daily interest: £60,000 × 0.0233% = £13.97
• 120 days: £1,676 in interest

Repayment interest works in your favour

If you overpay corporation tax — for example, you paid an estimate that proved too high — HMRC pays repayment interest back to you, currently at the base rate minus 1 percentage point (with a floor of 0.5%). This is one reason a sensible director facing uncertainty pays a slightly generous estimate by the deadline rather than risk underpaying: the cost of a modest overpayment is small, and the cost of underpaying is interest at 8.5%.

For the current published rates and how they have moved, see our HMRC interest rates guide.

Penalties for late filing of the CT600

Filing the CT600 return late is different — it triggers automatic, fixed penalties, and they apply even if you have already paid every penny of corporation tax owed. The return is a legal obligation in its own right.

The late filing penalty structure

The day-one £100 is automatic and lands quickly. The six- and twelve-month charges are tax-geared — they are a percentage of the tax, so a company with a large liability faces a far bigger penalty than one with a small one. A loss-making company with no tax to pay still gets the £100 + £100 fixed penalties.

Repeated late filing doubles the fixed penalties

If a company files its return late for three or more consecutive accounting periods, the two fixed penalties increase from £100 each to £500 each for the third and subsequent periods. Persistent lateness becomes materially more expensive.

Worked example: a 13-month-late return

A company owes £20,000 of corporation tax and files its CT600 13 months late:

• 1 day late: £100
• 3 months late: £100
• 6 months late: 10% of £20,000 = £2,000
• 12 months late: a further 10% = £2,000
• Total filing penalties: £4,200

That is on top of roughly 13 months of late payment interest on the £20,000 (around £1,800 at 8.5%) — a combined cost of about £6,000 on a £20,000 bill. For the complete breakdown, appeal routes and more examples, see our dedicated CT600 late filing penalties guide.

Penalty changes from April 2026

HMRC has been increasing the cost of non-compliance across the board. Several penalty and interest changes take effect in and around April 2026, raising the real cost of filing or paying late. We track these in corporation tax penalties doubling in April 2026 — if your year-end falls after April 2026, read it before assuming the figures above are the whole story.

What happens if HMRC does not receive a return: determinations

If you miss the 12-month filing deadline entirely, HMRC does not simply wait. It can issue a determination — its own estimate of the corporation tax due. A determination:

• Is HMRC's best guess at your liability, often deliberately high
• Cannot be appealed
• Is legally enforceable as if it were your own self-assessment — HMRC can pursue collection and use debt enforcement

The only way to displace a determination is to file the actual CT600 return, which replaces the estimate with your real figures. You generally have to do this within a limited window (broadly three years from the filing deadline). The lesson: a determination is not a way out of filing — it is a worse version of filing, with the tax set against you and no right of appeal.

If you cannot pay corporation tax on time

If you know you will not be able to pay by the deadline, contact HMRC before the deadline, not after. HMRC's Time to Pay service can spread a corporation tax bill over instalments — typically a few months, sometimes longer — if the company genuinely cannot pay in one go.

Key points about Time to Pay:

• Arrange it before the deadline wherever possible; HMRC is far more receptive to a company that gets ahead of the problem.
• Interest still accrues on the outstanding balance for the duration of the arrangement.
• You still have to file the CT600 on time — Time to Pay covers payment, not filing. Filing late will still trigger the £100 penalties.
• Keep to the agreed schedule; a defaulted arrangement can be cancelled and the full balance demanded.

Ignoring a corporation tax debt is the worst option. HMRC has strong enforcement powers, including direct recovery from company bank accounts, distraint, and ultimately a winding-up petition against the company.

Appealing a penalty: reasonable excuse

Late filing penalties can be appealed if you have a reasonable excuse — an unexpected event outside your control that stopped you filing on time. HMRC generally accepts things like:

• Serious illness or bereavement around the deadline
• A genuine HMRC online service failure
• Fire, flood or theft that destroyed your records
• Unexpected postal delays of HMRC documents

HMRC generally does not accept:

• "I forgot" or "I did not know the deadline"
• Pressure of work or being too busy
• Relying on an accountant who failed to act (HMRC expects you to check)
• Not having the money to pay (this is not an excuse for filing late)

If you have a reasonable excuse, you must file the return and put things right as soon as the excuse ends, then appeal in writing — normally within 30 days of the penalty notice.

Amending a corporation tax return

Found a mistake after filing? You can amend a CT600 yourself within 12 months of the filing deadline. After that window, corrections generally have to be made by writing to HMRC, and HMRC's own ability to open an enquiry has its own time limits (broadly 12 months from the date you filed, longer if the return was filed late or HMRC suspects careless or deliberate error).

This is another reason to file accurately and on time: a return filed on time starts the enquiry clock and gives you the cleanest, simplest route to fix genuine errors.

Special cases that catch directors out

Your first year. As covered above, first accounts covering more than 12 months mean two corporation tax periods and two returns. Do not assume one set of accounts equals one return.

A loss-making period. If your company makes a loss, there is no corporation tax to pay — but you still must file a CT600 to report the loss. Filing late still costs £100 + £100. Reporting the loss properly also lets you carry it forward against future profits, or in some cases carry it back for a refund. Loss planning is covered in our year-end tax planning guide.

A dormant period. A genuinely dormant company has no corporation tax payment or CT600 obligation for that period, but make sure HMRC's records actually show it as dormant — otherwise it will keep issuing notices to file and you will keep getting £100 penalties for not responding.

Closing the company. When a company ceases trading, its accounting period ends on the date trading stops, and a final CT600 covering the shortened period is due. Getting corporation tax cleared is a prerequisite for a clean strike-off or liquidation — see closing a limited company.

Changing your year-end. Any change to your accounting reference date moves every corporation tax deadline. Recalculate and reset reminders immediately.

How to make sure you never miss a corporation tax deadline

Missing these deadlines is almost always avoidable. The directors who get caught out are not the ones who do not care — they are the ones who lost track of dates that are 9, 12 and 16 months out. A few habits remove the risk entirely.

Record both deadlines the day your period ends. The moment your accounting period closes, put the payment date (9 months and 1 day) and the filing date (12 months) in your calendar with reminders at 3 months, 1 month and 2 weeks before each.

Finish your accounts before the payment deadline, not the filing deadline. Because you pay before you file, your accounts and tax computation need to be ready by month nine. Treat the payment date as the real deadline and the filing date as a buffer.

Pay an estimate if your figures are not final. If your accounts are not finished by the payment deadline, pay a sensible estimate based on management accounts. Overpayments are refunded with interest; underpayments cost 8.5%. Erring slightly high is cheap insurance.

Keep your bookkeeping current all year. Companies that fall behind on bookkeeping are the ones scrambling at year-end. Categorising transactions monthly means your accounts are largely ready when the period closes — and your tax estimate is reliable.

Use the correct payment reference and pay early. Use the 17-character reference for the current period, and send funds at least three working days before the deadline so they clear in time.

Engage your accountant early. Accountants are busiest in the weeks before common deadlines (January and March especially). Last-minute instructions lead to rushed work and missed dates. Brief them well in advance.

Use software that tracks the dates for you. Spreadsheets do not send reminders. A platform that calculates your deadlines from your year-end and alerts you in advance removes the single biggest cause of penalties — simply forgetting.

A complete worked example, start to finish

To pull all of this together, follow one company through its first full corporation tax cycle.

Bright Studio Ltd is incorporated on 12 May 2025 and starts trading the same week. Companies House sets its first accounting reference date as 31 May 2026 — a period of 12 months and 19 days.

Step 1 — Register for corporation tax. Within three months of starting to trade (by mid-August 2025), the director confirms through the HMRC online account that the company is active, using the UTR posted after incorporation.

Step 2 — Recognise there are two accounting periods. Because the first accounts span more than 12 months, corporation tax splits them:

• Period A: 12 May 2025 to 11 May 2026 (12 months)
• Period B: 12 May 2026 to 31 May 2026 (20 days)

That means two CT600 returns.

Step 3 — Work out the four deadlines.

Step 4 — Calculate the tax. Period A produces taxable profits of £90,000. That falls in the marginal relief band, so the company pays the 25% main rate less marginal relief — an effective rate of roughly 22.3%, giving corporation tax of about £20,050. Period B, just 20 days long, produces a small profit of £3,000, taxed at the 19% small profits rate (with limits proportionately reduced for the short period) — about £570.

Step 5 — Pay before you file. The director does not wait for the May 2027 filing dates. The company's bookkeeping has been kept current all year, so the accounts are ready by January 2027. The director pays £20,050 by 12 February 2027 and £570 by 1 March 2027, using the correct 17-character reference for each period, sent three working days early via Faster Payments.

Step 6 — File both returns. The two CT600 returns are submitted in April 2027, comfortably before the 11 May and 31 May filing deadlines.

Total penalties and interest: zero. The only thing that made this smooth was recognising the two-period split early and treating the payment dates — not the filing dates — as the real deadlines.

How AccountsOS tracks your corporation tax deadline

Keeping corporation tax deadlines straight by hand is exactly the kind of low-value, high-stakes task that software should own. AccountsOS does this automatically.

Automatic deadline calculation. When you set up your company in AccountsOS, the system records your accounting period end date and derives your payment deadline (9 months and 1 day) and your CT600 filing deadline (12 months) — including splitting a long first period into two corporation tax periods where needed.

Smart reminders. AccountsOS notifies you at 3 months, 1 month and 2 weeks before each deadline, so the date never sneaks up on you.

Real-time tax estimates. Throughout the year, AccountsOS estimates your corporation tax liability from your live profit figures — so you can budget for the payment, pay an accurate estimate if your accounts are not final, and avoid both underpayment interest and surprise bills.

Ask Finn in plain English. You can ask Finn, the AI built into AccountsOS, "when is my corporation tax due?" or "how much corporation tax will I owe this year?" and get an instant answer based on your actual numbers — no spreadsheets, no digging through HMRC's site.

One-click sharing with your accountant. Export your financial data or share workspace access so you and your accountant are always working from the same figures and the same deadlines.

Frequently asked questions

When is corporation tax due in the UK?

Corporation tax is due 9 months and 1 day after the end of your company's accounting period. For a 31 March 2026 year-end, payment is due by 1 January 2027. Companies with profits over £1.5 million pay earlier, in quarterly instalments.

Is the corporation tax payment deadline the same as the filing deadline?

No — and this catches many directors out. The payment deadline is 9 months and 1 day after your period ends. The filing deadline for the CT600 return is 12 months after your period ends. You pay roughly three months before you file.

What happens if I pay corporation tax late?

There is no fixed penalty for late payment, but interest accrues daily from the day after the deadline at around 8.5% per year (the Bank of England base rate plus 4 points). On a £10,000 bill paid 90 days late that is about £210; on larger bills it escalates quickly.

What happens if I file my CT600 late?

Late filing triggers automatic penalties: £100 at one day late, a further £100 at three months, then 10% of the unpaid tax at six months and another 10% at twelve months. File late three years running and the £100 fixed penalties rise to £500 each. See our CT600 late filing penalties guide.

How do I pay corporation tax?

Pay electronically — online or telephone banking (Faster Payments), CHAPS, Bacs, Direct Debit through your HMRC account, or debit/corporate credit card online. Always use the correct 17-character payment reference for the relevant accounting period, and allow at least three working days for funds to clear.

When do I need to register for corporation tax?

You must tell HMRC your company is active (has started to trade) within 3 months of starting business activity. HMRC sets up a corporation tax record automatically when you incorporate, but registration is not complete until you confirm the trading start date through your HMRC online account.

Why does my first year have two corporation tax returns?

Because a corporation tax accounting period can never exceed 12 months, but a first set of company accounts often covers more than 12 months. HMRC splits that long period into the first 12 months plus the remainder — two accounting periods, two CT600 returns, two payment deadlines.

Do I have to pay corporation tax if my company made a loss?

No. If your company made a loss there is no corporation tax for that period — but you still have to file a CT600 return to report the loss. Filing late still triggers the £100 + £100 fixed penalties. Reporting the loss also lets you carry it forward (or sometimes back) to reduce other years' tax.

Can I get a refund if I overpay corporation tax?

Yes. If you overpay — for example, you paid a cautious estimate that proved too high — HMRC refunds the excess and pays repayment interest on it. This is why paying a slightly generous estimate by the deadline is sensible when your final figures are not yet ready.

What if I cannot afford to pay corporation tax?

Contact HMRC before the deadline to arrange a Time to Pay instalment plan. Interest still accrues on the outstanding balance, and you must still file the CT600 on time — but a proactive arrangement avoids enforcement action and shows HMRC good faith.

Stay ahead of your corporation tax deadlines

Corporation tax is unforgiving in one specific way: the costs of getting it wrong — interest at 8.5%, automatic £100 penalties, tax-geared charges, determinations you cannot appeal — all stack up quietly while you are busy running the business. The deadlines themselves are simple. The problem is remembering them 9, 12 and 16 months out.

AccountsOS removes that risk. It calculates your payment and filing deadlines automatically, estimates your liability in real time so you are never guessing, and reminds you well before each date. You can ask Finn when your tax is due and get a straight answer in seconds.

See how AccountsOS compares to a traditional accountant, explore the features, or read our companion guides on filing the CT600 and corporation tax rates and thresholds.

Ready to stop worrying about deadlines? Start your free AccountsOS trial today and let automated accounting keep you compliant while you focus on growing your business.