Self Assessment Deadlines for 2025/26: What to File and When

The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Paper Self Assessment returns are normally due by 31 October 2026, while online returns and balancing payments are normally due by 31 January 2027.

If this is your first year needing Self Assessment, registration usually needs attention well before the filing deadline so HMRC can issue the right references.

The 31 January deadline is not only a filing date. It is also usually when any balancing tax for the previous tax year is paid, along with the first payment on account where one applies.

An accountant can help identify missing records, estimate the tax bill, check payments on account, and avoid the January rush. Waiting until late January often limits the advice available.

These are the standard dates. A notice issued at another time, certain partnership returns, trustees, non-resident companies or a different instruction from HMRC can produce another deadline. Check the notice and online account as well as this timetable.

Suppose the relevant Self Assessment amount for 2025/26 is £6,000 and no tax has been collected at source. If payments on account apply and no adjustment is made, 31 January 2027 could include the £6,000 balancing payment plus a £3,000 first payment on account for 2026/27. A further £3,000 would normally fall due on 31 July 2027.

The exact calculation excludes some liabilities and gives credit for tax deducted, so use HMRC’s statement rather than applying the example mechanically. If 2026/27 income is lower, a reasoned reduction claim may be possible, but interest can arise if reduced too far.

Submit an accurate return as soon as possible and do not delay filing only because payment is difficult. Filing and payment consequences are separate. HMRC may offer support or a Time to Pay arrangement based on circumstances, but contact should happen early.

If complete figures are not available, HMRC provides rules for provisional figures and later amendments. Mark estimates correctly and replace them promptly. Do not invent a number to make the filing look final.

Save the return, computation and submission receipt, then check the liability and payments shown in the HMRC account. Schedule both payment-on-account dates if they apply. If a figure changes, amend through the correct route and update the cash forecast.