Self Assessment deadlines and penalties

How the tax year links to deadlines

Self Assessment operates on the tax year from 6 April to 5 April. Deadlines are always expressed relative to the end of that tax year. For the 2024–25 tax year, which runs from 6 April 2024 to 5 April 2025, the key dates fall in autumn 2025 and winter 2026.

A return can be filed at any time after the tax year ends, provided it is on or before the relevant deadline. Many sole traders file soon after 5 April to settle the bill early or to arrange payments on account. Others work to the final online date in January. Both approaches are valid if the return is accurate and paid on time.

Registration for Self Assessment, where it is not already automatic, must happen earlier. Someone who becomes self-employed or starts receiving untaxed income must register in time to file by the deadline for the first return. Late registration does not extend the filing date and can compound penalty exposure.

Registration and notice to file

Before deadlines bite, HMRC must know who is in Self Assessment. A notice to file may arrive by post or through the online account. Filing is required even if no notice appeared, when a liability exists and a return is legally due.

Newly self-employed traders generally register for Self Assessment when they notify HMRC that they have started trading. Company directors who owe tax outside PAYE may need to register separately even if the company payroll already runs. The limited company director Self Assessment guide outlines when dividend and other income pulls directors into the system.

If HMRC issues a notice to file and the taxpayer is not actually liable — for example, because all income was taxed at source — the position should be clarified with HMRC promptly. Ignoring a notice on the assumption that no tax is due can still produce late-filing penalties until the matter is resolved.

Paper filing deadline — 31 October

Taxpayers who file on paper must send the return so it reaches HMRC by 31 October after the tax year end. For 2024–25, that is 31 October 2025.

Postage time counts. A return posted on 31 October may miss the deadline if it arrives late. Proof of posting helps in disputes but does not guarantee acceptance if the document arrived after the cut-off.

Paper filing is increasingly rare. Most traders file online because the January deadline is three months later and calculations are checked automatically. Anyone who opts for paper must also use paper for amendments in many cases, and supplementary pages must accompany the main return.

If paper is chosen, payment of tax is still due by 31 January unless HMRC agrees a Time to Pay arrangement. The October date is a filing deadline only; it does not advance the payment date.

Online filing deadline — 31 January

Online returns must be submitted by 31 January after the tax year end. For 2024–25, the deadline is 31 January 2026.

Filing online requires a Government Gateway account and, for returns that include certain income types, authorisation through additional security steps. Leaving first-time setup until the last week of January is a common cause of late filing. Account recovery and identity checks can take days.

The online system calculates tax automatically from the figures entered. Allowable expenses and reliefs claimed on the return directly affect the amount due. Traders who have not yet reconciled business records may benefit from reviewing the allowable expenses guide before entering profit figures under time pressure.

An online return submitted at 23:59 on 31 January is on time. Submissions after midnight count as the next day and attract penalties unless a reasonable excuse is accepted.

Payment deadlines

The main payment date for balancing tax owed for the tax year is 31 January following the year end — the same day as the online filing deadline. For 2024–25, tax due for that year is normally payable by 31 January 2026.

This January payment often includes more than the balancing figure for the year just ended. Taxpayers within payments on account also owe the first instalment for the current tax year on the same date. The combined amount catches many filers unaware; the payments on account guide explains that structure.

The second payment on account for a tax year is due on 31 July after the tax year end. For 2024–25, that is 31 July 2025 — before the return itself must be filed online. Cash-flow planning that looks only to January overlooks this midsummer date.

Capital Gains Tax on residential property disposals has a separate reporting and payment window — currently 60 days from completion for UK residents in many cases. That regime sits alongside Self Assessment, not instead of it, and missing it carries its own penalties.

Penalties for late filing

Late filing penalties apply automatically on a stepped basis. HMRC does not need to prove fault for the initial charges.

Stage	Typical consequence
One day late	£100 fixed penalty, even if no tax is owed
Three months late	£10 per day, up to 90 days (£900 maximum), on top of the £100
Six months late	the higher of £300 or 5% of tax due
Twelve months late	a further £300 or 5% of tax due, with possible higher penalties if withholding information is deemed deliberate

These amounts apply to each return outstanding. Old returns left unfiled continue to accrue charges until filed or formally withdrawn by HMRC.

Partnerships and individuals are penalised separately. A director late on a personal return faces personal penalties even if company accounts are up to date. Interest on unpaid tax runs from the original due date regardless of filing status.

Penalties and interest for late payment

Paying tax after 31 January triggers interest from the day after the deadline. HMRC publishes the rate on GOV.UK; it tracks Bank of England base rate plus a margin and can change during the year.

A late-payment penalty regime also applies to tax still unpaid after set intervals. Broadly, a charge of 5% of the unpaid tax can arise at five months after the due date, again at eleven months, and again at seventeen months, though the precise interaction with filing delays is detailed in HMRC guidance. Interest continues to accrue on the outstanding balance including any penalties that are themselves tax charges.

Partial payments reduce interest on the amount paid but do not stop penalties if the remainder is late. Setting up a Direct Debit for the budget payment plan or making a payment before filing can reduce exposure even when the return is not yet complete.

Time to Pay arrangements spread future payments but do not rewrite the original deadline for penalty purposes unless HMRC agrees terms that specifically address existing charges. Entering Time to Pay after the due date may still leave interest on the late period.

Reasonable excuse — what HMRC may accept

HMRC cancels penalties where a reasonable excuse existed for the entire period of failure and the failure was remedied without unreasonable delay once the excuse ended. The standard is narrow. GOV.UK and tribunal decisions emphasise that excuses must be serious, unforeseen, and outside the taxpayer's control.

Examples HMRC has accepted in published guidance and cases include the death of a close relative shortly before the deadline, an unexpected hospital stay, serious illness, computer failures while HMRC's own systems were working, and postal delays that could not be avoided when filing on paper. Each case depends on its facts.

Examples that are not normally accepted include insufficient funds to pay tax, relying on an agent who missed the deadline without the taxpayer taking reasonable care, missing the deadline through work pressure, or not knowing the rules. "My accountant was ill" may succeed only if the taxpayer could not reasonably have filed another way or appointed substitute help in time.

Evidence supports any appeal. Medical letters, death certificates, records of system outages, or proof that HMRC systems failed during submission attempts strengthen a claim. Appeals are made online, by post, or by phone depending on the penalty type, and must usually be lodged within 30 days of the penalty notice.

A reasonable excuse for filing late does not automatically cancel interest on late-paid tax unless the payment failure shared the same excuse. Filing and paying are judged separately.

Deadlines for amendments and corrections

After filing, errors can be corrected by amending the return. The amendment window for online returns is generally within 12 months of the filing deadline — so for 2024–25, until 31 January 2027. Paper returns follow a similar principle with paper amendment forms.

Discovering an error after the amendment window may require a formal disclosure to HMRC. Voluntary correction before HMRC spots the mistake often reduces penalty levels compared with an enquiry that uncovers the same error.

Amendments that increase tax due can create backdated interest to the original due date. Refunds from amendments are processed when HMRC accepts the revised figures.

Directors, sole traders, and overlapping obligations

Sole traders face one Self Assessment return covering personal and business income. Company directors may file a personal return for dividends, benefits, and other untaxed income while the company files accounts and Corporation Tax separately. Missing the personal 31 January deadline affects only the individual, but the same penalty ladder applies.

Employers with PAYE and VAT have additional calendars. Self Assessment does not replace those filings. A trader registered for VAT must still submit VAT returns on their own cycle even when the January Self Assessment date is the more visible deadline in planning.

Planning around the calendar

A practical approach is to treat 5 April as the close of books, complete records by summer, and file online in autumn when HMRC systems are quieter. That leaves time to budget for 31 January and 31 July payments, including payments on account.

Key dates for 2024–25, as an illustration:

• 31 July 2025 — second payment on account for 2024–25
• 31 October 2025 — paper return deadline for 2024–25
• 31 January 2026 — online return deadline and balancing payment for 2024–25; first payment on account for 2025–26

Dates shift one year forward for each subsequent tax year. HMRC occasionally announces short extensions after exceptional events, but relying on ad hoc relief is unsafe for routine planning.

Your next step

Anyone with a return due for the current tax year should confirm whether filing will be online or on paper and mark 31 January and, if applicable, 31 July in a payment calendar. Traders expecting their first substantial bill can read payments on account before the January deadline arrives.

Preparing figures early connects deadlines to accurate claims. The allowable expenses guide helps ensure profit is stated correctly before submission, and how to file Self Assessment walks through the filing steps themselves. Company directors with untaxed income should also review the limited company director Self Assessment guide for registration and return content specific to their position.