Corporation Tax
See your CT bill in real time. Generate the workpaper for filing.
Real-time Corporation Tax estimate from your live P&L, with marginal relief correctly calculated for the 19–25% banded regime (something most software gets wrong). Generates the CT600 workpaper as Excel — computation, marginal relief, S455, capital allowances and audit trail — ready to file.
In short
AccountsOS calculates Corporation Tax in real time from your live P&L, including the 19–25% banded marginal relief introduced in 2023 (most software gets this wrong). It generates a complete CT600 workpaper in Excel with the computation, marginal relief, S455 director-loan impact, capital allowances and a full audit trail — ready to give to your accountant or to file.
Free during Early Access — no credit card required
Everything Corporation Tax can do
Live CT estimate
- Pulls your live P&L and applies CT rules in real time
- Marginal relief banded calculation (correct for 2023+)
- Profit threshold awareness (£50k lower / £250k upper)
- Tax year filtering (UK April–April)
- Multi-trading-entity awareness (associates affect thresholds)
CT600 workpaper
- Generates an Excel workpaper ready for your accountant
- Includes the computation page
- Adjustments column for disallowables and capital allowances
- Marginal relief calculation worked through
- Director's loan (S455) impact pulled in automatically
- Audit trail for every adjustment
S455 director-loan tax
- Live DLA balance per director
- S455 deemed liability calculated when DLA is overdrawn
- 9-month repayment window countdown
- Plain-English explanation in chat
Capabilities at a glance
Real-time CT estimate from live P&L
Marginal relief done correctly (19–25% band)
CT600 workpaper export as Excel
S455 director-loan impact included
Capital allowances column
Multi-entity associate threshold handling
Audit trail for every adjustment
Tax-year-aware
How It Works
Run your books normally
Bank import, expenses, invoices — they post to the P&L via double-entry.
Open Corporation Tax
Your live CT estimate is shown instantly, with marginal relief if applicable.
Generate the workpaper
One click — get the Excel CT600 pack with computation, adjustments, marginal relief, S455 and audit trail.
File via your accountant
Hand the workpaper to your accountant for filing today. Direct CT600 e-submission to HMRC is on the roadmap.
By the numbers
Real-world Use Cases
Mid-year planning
See what CT you're on track to owe, decide whether to expense more before year-end.
Year-end with accountant
Hand them the workpaper. They check the adjustments column. File. Done.
Marginal relief sanity check
Profit lands between £50k and £250k? Most calculators get this wrong. Ours doesn't — and shows the maths.
Plays nicely with
Excel
LiveWorkpaper exports as XLSX with formulas intact.
HMRC CT e-filing
RoadmapDirect CT600 submission to HMRC.
Why founders pick this over the spreadsheet
No surprise tax bill at year-end
Marginal relief calculated correctly (lots of software doesn't)
S455 trap caught before it bites
Workpaper saves your accountant hours (you save fees)
Frequently Asked Questions
How accurate is the CT estimate?
It uses the same underlying logic as a CT600 — current rates (19% small profits, 25% main, marginal relief in between), tax year apportionment, and pulls in S455. Treat it as planning-grade until your accountant signs off, but it's the most accurate live estimate in any UK accounting product.
What's marginal relief, and why does it matter?
From April 2023 the UK CT rate is 19% if profits ≤ £50k, 25% if profits ≥ £250k, with a marginal relief calculation in between. Most software either ignores it or gets it wrong. We apply the formula correctly: the effective rate moves smoothly from 19% to 25% as profits cross the band.
Do you handle associates?
Yes — if you run multiple trading entities, the £50k and £250k thresholds are divided between associated companies. We surface this so you don't accidentally over-claim relief.
Can you file the CT600 directly?
Direct CT600 e-submission to HMRC is on the roadmap. Today the workpaper is ready for your accountant or for upload via HMRC's CT online service.
What about capital allowances?
The workpaper has a capital allowances column for AIA, FYA, WDA. You can override AccountsOS's suggested treatment per asset.
How does S455 affect this?
If a director has an overdrawn loan account at year-end, S455 deems a 33.75% tax charge unless repaid within 9 months. We pull that into the CT estimate automatically and warn you ahead of time.
Explore more of AccountsOS
Financial Reports
P&L, Balance Sheet, Trial Balance, Cash Flow Forecast — instant, accurate, exportable.
Director's Loan Account & S455
Stay out of the S455 trap. The DLA stays in the green or you hear about it.
Salary & Dividend Optimiser
Take the most home, legally. We do the maths every payroll cycle.
VAT & Making Tax Digital
VAT 9-box always live. File when you're ready.
Practitioner Tools (For Accountants)
Built so accounting practices can run client books too.
Ready to try Corporation Tax?
Get started with AI-powered accounting for your UK limited company.
Get Started FreeFree during Early Access — no credit card — cancel anytime