Corporate Income Tax Return (Form 1A)
Annual income tax return for Isle of Man resident companies. Filed with the Assessor of Income Tax within 12 months of the company's accounting year-end. There is no separate corporation tax in the Isle of Man — company income is assessed under the Income Tax Act 1970.
Who this applies to
- All Isle of Man tax-resident companies
- Foreign companies trading in the Isle of Man through a permanent establishment
- Isle of Man limited liability companies (LLCs) that have not elected transparent treatment
What to file
Form 1A (Company Income Tax Return) together with a copy of the audited or certified accounts, a computation of taxable income, and any supporting schedules for capital allowances, group relief, or losses.
How to file
Online via the Isle of Man Government's myGov.im portal, or by paper submission to the Assessor of Income Tax, Illiam Dhone House, 2 Circular Road, Douglas, IM1 1PQ. Electronic filing is preferred and may attract fewer errors.
Payment due
Tax is assessed and payable on the basis of the return. For standard 0% rate companies, no payment is due. For companies with banking, retail or land/property income, payment is due when the formal assessment is raised following the return — typically within 30 days of the notice of assessment.
Penalties for missing this deadline
A fixed penalty of £250 applies for failure to file within the 12-month deadline. Additional tax-related penalties apply if there is an understatement of liability. Interest on unpaid tax accrues from the date payment was due.
Filing checklist
- Prepare annual accounts to the company's year-end date
- Compute taxable income (income from land/property at 20%, banking income at 10%, all other income at 0%)
- Complete Form 1A on myGov.im
- Attach accounts and computation
- Submit any substance declaration if the company carries on a relevant activity
- File within 12 months of year-end
Common mistakes to avoid
- Missing the 12-month filing deadline — the IoM deadline is generous but many companies overlook it when focused on UK compliance deadlines
- Failing to classify land and property income at 20% — this is a common oversight for companies with mixed income streams
- Not filing the annual substance declaration alongside the return for relevant-sector companies
- Conflating the Isle of Man return with the UK corporation tax return — they are separate obligations for Isle of Man resident companies
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