Corporation Tax & CT600 filing software
Carry your accounts into the CT600, compute the tax with marginal relief, and file the return plus iXBRL computation to HMRC.
- 19–25%
- Rates, with marginal relief between
- 9m + 1d
- When the tax is due after year end
- iXBRL
- Accounts + computation tagged for you
A limited company has to turn its accounts into a CT600, get the adjustments and capital allowances right, apply marginal relief across the rate bands, and file iXBRL accounts and computations with HMRC — usually paying before the return is even due.
AI TaxPilot starts from your FRS 105/102 accounts, makes the tax adjustments, claims your allowances, applies marginal relief for the period, and files the CT600 with the iXBRL computation and accounts as one bundle to HMRC.
- CT600 built straight from your accounts
- Marginal relief and associated companies handled
- CT600 + iXBRL computation filed to HMRC
See it in action
A 48 seconds walkthrough of the real journey, end to end.
Start from your accounts
Your filed FRS 105 accounts flow straight in. We start from the profit per accounts — no re-keying.
What you get
Start from your filed FRS 105/102 accounts; the profit per accounts flows straight in.
Add back depreciation and disallowables, claim full expensing and the AIA in the right boxes.
Rate band and marginal relief computed for the period, divided by associated companies.
CT600A (loans to participators / s.455), CT600C (group relief) and others as you need them.
Accounts and the tax computation tagged as iXBRL and attached to the return.
Submit the CT600 + computation + accounts together and get the acceptance and IRmark back.
Calculators included
Free with your account, alongside the AI assistant and filing.
Learn the rules
Plain-English, sourced guides behind this solution.
Corporation Tax & the CT600: a director's guide
Rates, marginal relief, associated companies, capital allowances, losses, R&D relief and the deadlines every limited company must hit.
Companies House filing: accounts, confirmation statements & ECCTA
The three things every company must file, the new 2025 size thresholds, deadlines, late-filing penalties and the identity-verification changes now live.
Frequently asked questions
Can AI TaxPilot file my CT600 to HMRC?
Yes — it builds the CT600 from your accounts, computes the tax with marginal relief, and files the return with the iXBRL computation and accounts as one submission to HMRC.
Does it handle marginal relief and associated companies?
Yes — you tell it how many associated companies there are and it divides the £50,000/£250,000 limits and applies marginal relief for the period.
Does it produce the iXBRL accounts and computation?
It tags your accounts and tax computation as iXBRL and attaches them to the CT600, which HMRC requires for most companies.
When do I have to pay Corporation Tax?
Nine months and one day after your accounting period ends — before the CT600 itself, which is due twelve months after period end.
File your CT600 with confidence
Carry your accounts into the CT600, compute the tax with marginal relief and file the iXBRL bundle to HMRC.
Start freeNo card required.
This guide is general information, not personal tax advice, and reflects the rules we believe to apply as at June 2026 — rates and thresholds change. Always check your own figures against HMRC and consider a qualified adviser before acting. You remain responsible for the accuracy of anything you file.