Self Assessment Readiness Checklist

Why this checklist matters

HMRC's Self Assessment system catches almost everyone who has income outside standard PAYE. The two most expensive mistakes are missing the 31 January filing deadline (an automatic £100 penalty that escalates daily) and underestimating which sources of income actually need declaring. This checklist exists to surface both before the deadline arrives.

Who needs to file Self Assessment in 2026/27

You almost certainly need a Self Assessment return if any of these apply during the 2025/26 tax year (which the 31 January 2027 return covers):

• You were self-employed and earned more than the £1,000 trading allowance
• You had untaxed income above £2,500 (rent, dividends, foreign income, freelance work)
• Your taxable income exceeded £150,000
• You or your partner earned over £50,000 and one of you received Child Benefit (HICBC applies)
• You sold something that triggered Capital Gains Tax — including crypto disposals above the £3,000 untaxed income, or a
• You were a company director with untaxed income, or a partner in a partnership
• You received foreign income above £2,000 even if remitted to the UK

If you only have PAYE income and your tax code is correct, you usually don't need to file — but HMRC may still issue a return if your circumstances look complex. If you get a notice to file (form SA316), you must respond by the deadline whether or not you owe tax.

Key dates for the 2025/26 return

5 October 2026 — deadline to register for Self Assessment if it's your first year. 31 October 2026 — paper return deadline (most people file online instead). 31 January 2027 — online return deadline AND balancing payment deadline. 31 July 2027 — second payment-on-account deadline if you owe more than £1,000 in tax. Missing any of these triggers penalties; missing 31 January triggers an automatic £100 fine even if you owe nothing.

Authoritative reference: gov.uk Self Assessment hub, including the official "Check if you need to send a Self Assessment tax return" tool which mirrors much of the logic in this checklist.