Budget 2026: what it means for you and your business —
In short
Your corporation tax is payable nine months and one day after the end of your accounting period, and the CT600 return is due twelve months after it — so the tax falls due before the return does. HMRC’s free online filing service closed on 31 March 2026, so every company must now file using commercial software. LMJ Group prepares your computation, files the CT600, and includes the software.
Payment: nine months and one day after the end of your accounting period. Return (CT600): twelve months after the end of the period.
Read that again — the money is due three months before the paperwork is. This is the most common cash-flow shock for owner-managed companies, and it is entirely avoidable with a forecast.
Large companies pay by quarterly instalments instead, starting during the accounting period itself. Very large companies pay earlier still.
No. HMRC’s free Corporation Tax online filing service closed on 31 March 2026. Every UK company must now file its CT600 and accompanying accounts using commercial software.
If you previously filed yourself through the HMRC portal, you now need either a software licence of your own or an agent who has one. We include the software as part of our compliance service, so there is nothing for you to buy, learn or configure.
Your accounting profit is not your taxable profit. The computation adjusts it:
Add back disallowable items — depreciation, most business entertaining, statutory fines and penalties. Deduct capital allowances in place of depreciation, including full expensing on qualifying plant and machinery. Apply loss relief, group relief and any available reliefs such as R&D. Then determine the rate band — 19%, 25%, or marginal relief in between, remembering that associated companies divide the thresholds.
Each of those steps is a place where tax is either saved or wasted.
HMRC applies penalties starting at £100 for a return one day late, rising with further delay, and doubling for repeated lateness. Interest also runs on unpaid tax from the due date — which, remember, was three months before the return deadline.
A persistent pattern of late filing also raises your risk profile with HMRC and increases the likelihood of an enquiry.
This page covers preparing and filing the return. Reducing the bill — capital allowances timing, associated companies, pension contributions, R&D, profit timing — sits under Corporation Tax Planning. Filing a return accurately does not, by itself, save you a penny.
Software included — no scramble now HMRC’s free filing service has closed.
Payment forecast in advance — the tax is due before the return; you’ll know well ahead.
Computation reviewed by a chartered adviser, not just processed.
Joined up with planning — we tell you what to do *before* the year end.
Never filed late.
This page provides general information about the 2026/27 UK tax year and is not advice on your particular circumstances. Tax and regulatory rules change frequently. Please contact us before acting, or refraining from acting, on anything set out here. LMJ Group is a firm of Chartered Accountants regulated by the ICAEW. LMJ Group is not a registered auditor and does not provide audit services. Last reviewed: July 2026.
