UK accounting filing deadlines in 2026: the complete calendar

For a UK practice, the calendar is the job. Miss a Confirmation Statement and Companies House starts a strike-off clock; miss a VAT payment and HMRC's penalty points tick up. This guide sets out the statutory filing deadlines that shape a 2026 workload, and — more usefully — the rule that produces each one, so you can reproduce the date for any client regardless of their year-end.

The fixed dates every UK practice already knows

A handful of deadlines land on the same date for almost everyone, which makes them the anchors of the compliance year:

• 31 January 2026 — online Self Assessment filing and balancing payment for the 2024/25 tax year, plus the first payment on account.
• 6 July 2026 — P11D and P11D(b) returns for expenses and benefits in the 2025/26 tax year.
• 31 July 2026 — second Self Assessment payment on account for 2024/25.
• 5 October 2026 — deadline to register for Self Assessment if you became liable during 2025/26.
• 31 October 2026 — paper Self Assessment filing for 2025/26.

The moving deadlines: worked out per client

Most of a practice's deadlines are not fixed dates at all — they are derived from each client's own year-end or VAT stagger. These are the ones spreadsheets get wrong, because every client has a different anchor.

Annual accounts (Companies House)

Private companies must file accounts within nine months of the accounting reference date (ARD). A company with a 31 March 2026 year-end therefore files by 31 December 2026. A first set of accounts runs 21 months from incorporation instead.

Corporation Tax (HMRC)

Payment is due nine months and one day after the end of the accounting period; the CT600 return is due twelve months after period end. So the same 31 March 2026 year-end means Corporation Tax paid by 1 January 2027 and the return filed by 31 March 2027 — the pay-before-you-file gap that catches out new company directors.

Confirmation Statement (Companies House)

Due within 14 days of the end of the review period, which is usually the anniversary of incorporation or of the last statement. It is cheap to file and expensive to forget: a persistently overdue statement can trigger strike-off proceedings.

VAT returns and payments (HMRC)

For standard quarterly VAT, the return and payment are both due one calendar month and seven days after the period end. A client on the stagger group ending 31 March 2026 files and pays by 7 May 2026. Since Making Tax Digital, these must be submitted through compatible software.

The pattern to remember: fixed dates are the same for every client; derived dates change with each client's ARD or VAT stagger. It's the derived dates that need a system, not a spreadsheet.

Weekends and bank holidays

Where a deadline falls on a weekend or a UK bank holiday, the practical position varies by authority and filing type — some are treated as due the next working day, others are not. Building the raw statutory date is only half the job; adjusting it correctly for the 2026 bank-holiday calendar is what separates a reminder that helps from one that quietly misleads.

Turning the calendar into a system

The safest way to run this is to record each client's anchors once — entity type, ARD, VAT stagger, payroll and Self Assessment obligations — and let those anchors generate a rolling schedule. That is exactly what FilingKeeper does: you add a client, and every derived deadline appears, adjusted for weekends and bank holidays, with reminders before each one.

This article is general guidance, not tax advice. Always confirm a client's specific obligations against current HMRC and Companies House guidance.