Who can file their own accounts in 2026
In April 2025 the company size thresholds rose by roughly half. A company is now a micro-entity if it meets two of three: turnover up to £1m, balance sheet up to £500k, up to 10 employees. That covers the overwhelming majority of owner-managed companies — and a micro-entity may prepare the radically simpler FRS 105 accounts: a short profit and loss, a short balance sheet, no notes beyond a handful of statutory statements, no audit.
There is no law requiring an accountant. The requirement is that the filings are correct and in the registers' machine-readable format — which is a software problem, not a judgement problem, for a company whose year is simple.
The three documents the job actually is
"Filing your accounts" is really three documents to two registers, and the figures must agree across all of them:
- FRS 105 accounts to Companies House — as iXBRL, tagged against the FRC taxonomy, balance sheet balancing to the penny.
- The CT600 to HMRC — the corporation tax return itself, with its box-level arithmetic cross-checked by HMRC's rules the moment it arrives.
- Tax computations attached to the CT600 — an iXBRL document showing how accounts profit became taxable profit became tax. HMRC rejects returns whose computations are missing or disagree with the CT600.
Why you can't just do this by hand
Three deadlines that don't line up
- Accounts to Companies House
- 9 months after your accounting reference date (21 months for a first year).
- Corporation tax payment
- 9 months and 1 day after the end of the accounting period — BEFORE the return is due.
- CT600 to HMRC
- 12 months after the end of the accounting period.
The order surprises people: the money is due to HMRC three months before the return is. Filing early solves this neatly — the return tells you the exact figure to pay, with months to spare.
What you need before you start
- Your company's 10-digit UTR from HMRC's letters, and a Government Gateway account with Corporation Tax enrolled — not just the letter.
- Your Companies House authentication code for the accounts.
- The year's figures: turnover, allowable expenses, what the company owns at year end, and share capital. A trial balance export from your bookkeeping covers all of it.
The first-year trap: two tax returns
A first accounting period usually runs from incorporation to the end of the month a year later — more than 12 months. Companies House takes one set of accounts for the whole period, but HMRC caps a CT600 at 12 months, so a long first year means two returns, each with its own payment deadline and its own 17-character payment reference. Software that understands the split prepares both; software that doesn't leaves you with a mystery rejection.
When not to do it yourself
DIY filing is for simple years. Hand the job to an accountant — and gladly pay them — if the year involves R&D claims, a director's loan that needs a CT600A, group structures, losses you want carried back, investment property, or any figure you can't confidently stand behind. Software makes the mechanical half cheap; it does not replace judgement, and anyone who says otherwise is selling you a penalty.
How WrenTax does it
You enter eight figures — or import a trial balance CSV and check the mapping. WrenTax computes the tax (marginal relief and first-year splits included), builds all three documents so the figures agree by construction, and shows you every one of them free before you pay £59. Submission goes to both registers with each acknowledgement tracked live, and if a register rejects, you see the reason in plain English and refile free — or get the fee back. Not tax advice; software for the mechanical half, done properly.