UK Tax Return Deadlines and Penalties Explained

The Self-Assessment system runs to a strict calendar set out in the Taxes Management Act 1970 and Finance Act 2009. Most taxpayers in scope for SA know the headline 31 January online deadline; fewer know the registration deadline, the paper deadline, the payments on account schedule, or the penalty escalation that runs through the year that follows a missed filing.

This guide walks through each deadline, the penalty consequences of missing it, and the practical routes to appeal where there is a reasonable excuse. Figures and statute references are current to 2026/27.

The annual filing calendar

The UK tax year runs 6 April to 5 April. For the 2026/27 tax year, the registration deadline for new self-employed individuals or those with new untaxed income sources is 5 October 2027, the paper return deadline is 31 October 2027, the online return deadline is 31 January 2028, the first payment on account is 31 January 2028, the balancing payment for 2026/27 is 31 January 2028, and the second payment on account is 31 July 2028.

The 31 January deadline carries both a filing and a payment obligation: the return must be submitted and any tax due paid by midnight. The payment includes the balancing payment for the year just ended plus the first payment on account for the next year where one is due (broadly where total bill exceeded GBP 1,000 and less than 80% was collected through PAYE).

Worked example: a self-employed designer's 2026/27 bill is GBP 6,000. The 31 January 2028 payment is GBP 6,000 balancing plus GBP 3,000 first payment on account, totalling GBP 9,000. The 31 July 2028 second payment is GBP 3,000. The 31 January 2029 payment will be the balancing payment for 2027/28 plus the first payment on account for 2028/29.

Edge case: where total income tax and Class 4 NI is less than GBP 1,000, or where more than 80% has been collected through deduction at source (PAYE, CIS), no payments on account are due and the entire balance is paid by 31 January.

Schedule 55 penalty escalation

Late filing penalties under Schedule 55 Finance Act 2009 follow a fixed escalation regardless of whether tax is owed. An immediate GBP 100 fixed penalty applies as soon as the deadline passes. After three months daily penalties of GBP 10 a day accrue for up to 90 days, a maximum of GBP 900 in daily penalties.

At six months a further tax-geared penalty applies: the greater of 5% of the tax due or GBP 300. At twelve months a second tax-geared penalty of 5% or GBP 300 applies (rising to 70% or 100% in cases of deliberate concealment under paragraph 6 of Schedule 55). The total fixed-plus-daily penalty for a year of non-filing therefore reaches a minimum of GBP 1,600 even where no tax was due.

Worked example: a taxpayer fails to file a 2026/27 return that had GBP 4,000 of tax owing. By 1 February 2029 (one year late) the penalties accrued are GBP 100 (initial), GBP 900 (90 days daily), GBP 300 (six month minimum; greater than 5% of GBP 4,000 = GBP 200) and GBP 300 (twelve month minimum), totalling GBP 1,600, plus interest on the GBP 4,000 from 1 February 2028.

Practical action: filing the return as soon as possible after missing the deadline stops the daily charges accruing once filed. The initial GBP 100 still applies but the GBP 10 per day stops on the date of filing.

Late payment penalties and interest

Late payment penalties under Schedule 56 Finance Act 2009 are separate from late filing. A 5% penalty applies on tax unpaid 30 days after the due date, a second 5% at six months, and a third 5% at twelve months. These are charges on the tax balance, additional to the filing penalties above.

Interest on unpaid tax runs from the original due date under section 101 Finance Act 2009. The HMRC late payment interest rate is set as base rate plus 2.5 percentage points and is updated within weeks of any Bank of England base rate change. For periods through 2026 it has typically run between 7% and 8.5%.

Worked example: GBP 4,000 of tax unpaid for one year would accrue around GBP 290 of interest at 7.25%, plus three 5% penalties of GBP 200 each (GBP 600 total). The combined late payment cost of GBP 890 sits on top of any late filing penalties already imposed.

Edge case: HMRC offers a Time to Pay arrangement where a taxpayer cannot pay on time. Setting up an arrangement before the 30-day late payment penalty bites prevents that first 5% penalty, but interest continues to accrue on the outstanding balance throughout the arrangement.

Reasonable excuse and appeal routes

HMRC accepts that penalties may be cancelled where the taxpayer has a reasonable excuse for the failure under section 118 Taxes Management Act 1970. The bar is relatively narrow: serious illness, bereavement of a close family member, fire or flood destroying records, software failure on the HMRC service near the deadline, or postal failures supported by documentary evidence.

Pressure of work, lack of awareness of the obligation, or an agent's failure to file are not normally accepted as reasonable excuses by HMRC, though some cases have succeeded at tribunal where the taxpayer had taken reasonable steps to instruct the agent. The case law in the First-tier Tribunal has gradually broadened what counts as reasonable, particularly around remote-working software failures.

The appeal route is first a written appeal to HMRC within 30 days of the penalty notice, explaining the excuse and supporting evidence. If rejected, the taxpayer can request an HMRC statutory review or appeal directly to the First-tier Tribunal (Tax Chamber). The tribunal application has a separate 30-day window from the HMRC review decision.

Practical action: lodging the appeal even at outline level within 30 days preserves the right to argue the point. Supporting evidence can be added later; the key is to start the process rather than waiting until the full case file is ready.

Common mistakes and HMRC flags

The most common avoidable errors in Self-Assessment are: underestimating untaxed savings interest where banks no longer deduct tax at source, omitting employer benefits in kind reported on P11D, missing dividend income from non-ISA brokerage accounts, underestimating rental income net of allowable expenses, and failing to declare cryptoasset disposals that pass the proceeds test.

HMRC's data feeds from banks (under the Common Reporting Standard since 2017), brokers, employers (Real Time Information) and the Land Registry mean omitted income is often matched against the SA return. A compliance check letter is the typical first contact, asking the taxpayer to explain a specific discrepancy. Cooperation at that stage usually keeps the matter out of a formal section 9A enquiry.

The High Income Child Benefit Charge is a common trip wire: couples where one earner exceeds GBP 60,000 must file SA if Child Benefit was received, and the charge tapers fully out at GBP 80,000 (rates set from 6 April 2024). Forgetting to register for SA when the charge becomes due triggers both filing and payment penalties.

Practical action: cross-checking the SA return against bank interest summaries (issued by January), P60 and P11D from employers, broker year-end summaries, and rental records before filing reduces the risk of HMRC follow-up. Where uncertain, filing an estimate and noting that a corrected figure will follow stops the late-filing clock while allowing a section 9ZA amendment within 12 months of the deadline.

Frequently asked questions

What is the deadline for online Self-Assessment in 2027?

31 January 2028 for the 2026/27 tax year. The return must be filed and any tax due paid by midnight on that date. Paper returns for the same year had to be filed by 31 October 2027. Missing the online deadline triggers an immediate GBP 100 fixed penalty under Schedule 55 Finance Act 2009 regardless of whether tax is owed, with daily penalties accruing after three months.

Do I need to file Self-Assessment if I owe no tax?

Yes if HMRC has issued a notice to file or if the conditions in section 7 Taxes Management Act 1970 apply (self-employed turnover above GBP 1,000, partner in a partnership, untaxed income above GBP 2,500, dividends above GBP 10,000, CGT proceeds above the reporting threshold, HICBC liability). The filing obligation runs regardless of tax owed. Where genuinely no longer in scope, requesting withdrawal of the notice through the Personal Tax Account or by writing to HMRC is the correct route.

How much is the late filing penalty?

Initial GBP 100 from the day after the deadline, regardless of tax owed. Daily GBP 10 penalties from three months late for up to 90 days (maximum GBP 900). Tax-geared penalty of 5% of tax due or GBP 300 (whichever is greater) at six months. A second 5% or GBP 300 at twelve months. The total minimum penalty for a year of non-filing is GBP 1,600 even where no tax is owed.

Can I appeal a late filing penalty?

Yes, in writing within 30 days of the penalty notice, citing a reasonable excuse under section 118 Taxes Management Act 1970. Accepted excuses include serious illness, bereavement, fire or flood, or HMRC system failure near the deadline. Pressure of work and agent failure are not normally accepted. If HMRC rejects the appeal, a statutory review or First-tier Tribunal appeal follows. The appeal must be lodged even at outline level within the 30-day window to preserve rights.

What if I can't pay the tax on time?

Set up a Time to Pay arrangement with HMRC through the Personal Tax Account or by phone on 0300 200 3820. An arrangement set up before the 30-day late payment penalty bites avoids that first 5% penalty. Interest continues to accrue on the outstanding balance at the official rate (base rate plus 2.5 percentage points). HMRC will usually agree to monthly instalments over up to 12 months for amounts under GBP 30,000 without detailed financial review, subject to compliance history.