File your Corporation Tax (CT600)
Carry your accounts into the CT600, let us handle marginal relief and the adjustments, and file the return plus computation to HMRC.
Start from your accounts
Your filed FRS 105 accounts flow straight in. We start from the profit per accounts — no re-keying.
Step by step
The same journey, written out — so you can read it at your own pace.
- Start from your accounts
Your filed FRS 105 accounts flow straight in. We start from the profit per accounts — no re-keying.
- Adjustments & allowances
The wizard adds back depreciation and disallowables and claims your capital allowances — full expensing and the AIA — in the right boxes.
- Marginal relief, computed
We work out the rate band, apply marginal relief for the year and show the computation line by line — exactly how HMRC expects it.
- Review the CT600
A full check of the return and the iXBRL computation, with every relief and adjustment evidenced before anything is sent.
- File to HMRC
The CT600, computation and accounts go to HMRC together as one iXBRL submission. The acceptance and IRmark come straight back.
Common questions
Does it handle associated companies?
Yes — you tell us how many associated companies there are and we divide the £50,000/£250,000 marginal-relief limits accordingly.
Can I file the accounts and CT600 together?
You can file accounts at Companies House and the CT600 (with the accounts and computation as iXBRL) at HMRC — both from the same company record.
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 freeThis 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.
Go deeper
The full guides and articles behind this journey.
Rates, marginal relief, associated companies, capital allowances, losses, R&D relief and the deadlines every limited company must hit.
The three things every company must file, the new 2025 size thresholds, deadlines, late-filing penalties and the identity-verification changes now live.
More flight plans
File your Self Assessment
From a blank return to filed-with-HMRC in one sitting — your figures pulled in, the maths checked, the SA100 submitted.
Build & file your company accounts
Turn a year of bank transactions into FRS 105 micro-entity accounts and file the iXBRL to Companies House — without a spreadsheet in sight.
Connect HMRC and pre-fill everything
One secure connection pulls your tax record into AI TaxPilot — and pre-fills every calculator and wizard, with each figure tagged to its source.