UK Self Assessment Penalty Calculator

Under the existing regime, £100 immediately — even if you owe no tax at all. From three months late HMRC can charge £10 per day for up to 90 days, a maximum of £900. At six months a further penalty of the greater of £300 or 5% of the tax due applies, and the same again at twelve months. A return twelve months late on a £18,000 liability therefore carries £100 + £900 + £900 + £900 = £2,800 in filing penalties alone.

Yes, under the existing regime. The £100 initial late filing penalty is fixed and applies regardless of your liability, so a nil return filed one day late still costs £100. Only the tax-geared elements at six and twelve months depend on what you owe, and even those carry a £300 minimum. This is why filing on time matters even in a year where you are due a refund.

From 6 April 2026 taxpayers mandated into Making Tax Digital for Income Tax move to a points-based late submission regime. You receive one point for each missed submission. For annual obligations a £200 penalty is charged once you reach two points; for quarterly updates the threshold is four points. Points expire after 24 months provided the threshold has not been reached. It replaces the fixed £100 for those taxpayers only — everyone else stays on the existing rules for now.

Sole traders and landlords with qualifying income above £50,000 were mandated from 6 April 2026, with the threshold stepping down to £30,000 in April 2027 and £20,000 in April 2028. Qualifying income means gross trading and property income before expenses, so a landlord with £55,000 of rent and a small profit is still within scope. If you are not mandated, the existing penalty regime continues to apply to you.

Under the existing regime, 5% of the unpaid balancing payment at 30 days, another 5% at six months and another 5% at twelve months — 15% in total if the bill sits unpaid for a year. Under the new regime the pattern changes to 3% of the outstanding tax at day 15, a further 3% at day 30, then 10% per annum accruing daily from day 31. Late payment penalties are separate from and additional to late filing penalties.

7.75%, effective from 9 January 2026. Late payment interest is fixed in legislation at the Bank of England base rate plus four percentage points, and with the base rate at 3.75% that gives 7.75%. Repayment interest, which HMRC pays you on overpayments, is base rate minus one at 2.75%. Interest is not a penalty, so there is no reasonable excuse defence — it simply accrues from the due date.

Yes, normally within 30 days of the penalty notice, if you have a reasonable excuse. HMRC accepts serious illness, a bereavement close to the deadline, unexpected hospital stays, service issues with HMRC's own systems, and events like fire or flood that destroyed records. It does not generally accept finding the system too difficult, not receiving a reminder, or relying on someone else to file unless you took reasonable care to ensure they did. Appeal online or on form SA370.

The filing penalties stop, which is the larger of the two. Filing on time and paying late attracts the late payment penalties and interest only; failing to file attracts both sets. If you cannot pay, file anyway and then set up a Time to Pay arrangement, ideally before the deadline. Doing so prevents further late payment penalties accruing on the amounts covered, though interest continues on the outstanding balance throughout.

There is no general cut-off for returns that were never filed — HMRC can issue determinations and penalties for old years, and the tax-geared penalties keep applying. Where HMRC has not issued a notice to file, the position differs, because the penalty attaches to a failure to comply with that notice. If you have several years outstanding, the practical route is usually a voluntary disclosure rather than filing them one at a time and waiting for penalty notices.

That is a separate offence — failure to notify chargeability — with its own penalty based on the potential lost revenue and on your behaviour, ranging from nil for a genuine mistake disclosed unprompted to 100% for deliberate concealment. The deadline to register is 5 October following the end of the tax year. Failure to notify penalties can exceed late filing penalties substantially, and unprompted disclosure reduces them far more than prompted disclosure.

They can be considerably higher. Offshore matters carry their own penalty scale geared to the source jurisdiction: up to 100% of the potential lost revenue for territories that exchange information with the UK automatically, 150% for exchange on request, and 200% for those that share nothing. Separately, Failure to Correct rules apply to pre-6 April 2016 offshore years with a penalty floor of 100% of the tax even on an unprompted, fully cooperative disclosure.

UK penalties and interest are not creditable against US tax. Only the UK tax itself qualifies for the foreign tax credit on Form 1116 — penalties and interest are expressly excluded. So a late UK filing costs you the full penalty with no American offset, while the underlying tax may cost you very little on a net basis after credit relief. That asymmetry makes timeliness disproportionately valuable for dual filers.

Indirectly. Payments on account are set at 50% of the previous year's Income Tax and Class 4 National Insurance, so until the late return is filed HMRC has no updated figure and may issue determinations or continue using an old one. Filing brings the figures up to date and can reduce future instalments, but any balancing payment then becomes due immediately with late payment penalties already accrued from the original date.

Filing with provisional figures is permitted and is usually better than filing nothing, provided you tick the box indicating provisional figures and amend once the real numbers are available. It stops the escalating late filing penalties. What it does not do is protect you from inaccuracy penalties if the estimates are careless rather than genuinely provisional, so the estimates need a reasonable basis you could explain later.