Self Assessment Penalty Calculator

Estimate your penalty above

Pop your figures into the calculator at the top of this page: the tax you owe, the deadline you missed and how late you are. It returns a guide total combining the late filing penalty, the late payment penalty and interest. The sections below explain exactly how each charge is worked out so the number makes sense, not just appears.

How HMRC late return and late payment penalties work

Self Assessment has two completely separate sets of penalties, and missing both deadlines means you can be charged twice over for the same year. The first set is for filing the return late. The second is for paying the tax late. On top of those, HMRC adds daily interest on any tax you have not paid.

The online filing deadline is 31 January after the tax year ends. So a 2025/26 return is due by 31 January 2027, and a 2026/27 return by 31 January 2028. The paper deadline is earlier, on 31 October. The balancing payment for your tax bill is due on the same 31 January date as the online return.

Late filing penalties

The late filing penalty follows a fixed staircase set out in law, and the early charges apply even if you owe no tax at all:

• Day after the deadline: an automatic fixed penalty for missing the filing date.
• From 3 months late: daily penalties start to accrue for each further day the return is outstanding, capped after 90 days.
• At 6 months late: a further penalty, charged as the greater of a fixed amount or a percentage of the tax due.
• At 12 months late: another penalty on the same greater-of basis, which can be higher still in serious cases.

Because the daily charges only begin once you are three months late, the difference between filing in February and filing in May is large. The exact current amounts are published by HMRC, linked in the table below.

Late payment penalties and interest

Paying late triggers its own penalties at roughly 30 days, 6 months and 12 months after the payment deadline, each calculated as a percentage of the tax still outstanding at that point. Separately, HMRC charges interest on the unpaid tax every day from the due date until you clear it. That late payment interest rate is tied to the Bank of England base rate plus a margin, so it moves over time. Check the live figure on gov.uk rather than assuming last year's rate, and treat the interest part of any estimate as approximate.

Worked examples with the maths shown

Penalties are easier to grasp with real numbers. Here are two common situations.

Example 1: a nil or small bill, filed a few weeks late

Imagine you are a part-time freelancer who registered for Self Assessment but, after expenses, owe nothing for the year. You forget the deadline and file six weeks late. There is no tax to pay, so there is no late payment penalty and no interest. But the fixed late filing penalty still applies in full because it is charged regardless of the tax owed. The lesson: a return showing zero tax is not a free pass. File it to avoid a penalty for nothing.

Example 2: a sole trader five months late with tax owed

Say you are a self-employed electrician with a balancing payment of £3,000 for the year, and you file your return and pay five months after the 31 January deadline. Work through the charges in order:

• Fixed filing penalty: applied the day after the deadline.
• Daily filing penalties: these run from the 3-month point. At five months late you are roughly two months - about 60 days - past that mark, so daily charges have been stacking up for around 60 days.
• Late payment penalty: the first late payment penalty is a percentage of the unpaid tax once you pass 30 days late. On £3,000 owed, a 5% charge would be 0.05 × £3,000 = £150.
• Interest: daily interest has been running on the full £3,000 from 1 February until the day you pay.

The filing penalties here are driven by time, the £150 payment penalty is driven by the size of the bill, and the interest is driven by both. Filing the return promptly even if you cannot pay yet would stop the daily filing penalties dead, while you arrange the tax separately.

Why paying down the tax early matters

The 6 and 12-month late payment penalties are percentages of what is still outstanding at those dates. If you clear most of the £3,000 before the six-month mark, those later percentage penalties bite on a smaller balance, and the daily interest also falls because it is charged on the reducing amount. Part payments genuinely reduce the damage.

2026/27 deadlines and where the penalty figures come from

The penalty amounts and the late payment interest rate are set by HMRC and updated over time, so always confirm the current figures rather than relying on memory. The table summarises the key dates for the 2026/27 cycle.

For the official penalty amounts and the current interest rate, see HMRC's guidance on penalties for late filing and late payment and the tool to estimate your Self Assessment penalties. If money is tight, MoneyHelper has free guidance on dealing with tax debt.

How to reduce or avoid the penalty

You have more options than many people realise:

• File first, pay second. Submitting the return stops the filing penalties even if you cannot yet pay the tax. The two clocks are independent.
• Set up a Time to Pay arrangement. HMRC lets many people spread Self Assessment debt over monthly instalments. Agreeing one can prevent further late payment penalties, though interest still runs.
• Claim a reasonable excuse. If something genuinely outside your control stopped you filing or paying on time, such as a serious illness, a bereavement or a fault in HMRC's own service, you can appeal a penalty. Routine pressure of work or losing your password usually does not count.
• Check whether you even needed to file. If HMRC issued a return in error, ask for it to be withdrawn, which removes the filing penalty. Our do I need to file a tax return checker can help you confirm.
• Reduce payments on account. If your income has dropped, you may be paying too much upfront. See the payments on account calculator before assuming a figure is right.

Common mistakes people make

• Assuming no tax means no penalty. The fixed late filing penalty applies even on a nil return.
• Confusing the two deadlines. Filing on time but paying late, or vice versa, still triggers one set of penalties.
• Ignoring interest. It accrues daily and is easy to overlook because it is not a one-off charge.
• Waiting until you can pay in full before filing. This lets daily filing penalties pile up needlessly.
• Forgetting payments on account. The 31 January bill often includes a payment towards next year, so the amount due, and any penalty based on it, can be larger than expected. Check your wider position with the Self Assessment tax calculator or the self-employed tax calculator.

Penalties are largely the same across England, Wales, Scotland and Northern Ireland because Self Assessment is run UK-wide by HMRC. The underlying tax can differ for Scottish taxpayers, who have their own income tax rates and bands, but the late filing and late payment penalty regime itself is the same wherever you live in the UK.

These figures are estimates for guidance only and not personal tax or financial advice. Confirm the current penalty amounts and interest rate with HMRC, and seek advice if your situation is complex.

Related tools to stay on top of your tax

Plan ahead so penalties never start. Track key dates with the tax deadline tracker, work out interest separately with the late payment interest calculator, and size up your bill early using the Self Assessment tax calculator.

Who should use this calculator

Works out what filing or paying late will cost. The structure is worth knowing because it escalates sharply: an immediate fixed penalty, then daily penalties after three months, then percentage-based penalties at six and twelve months — alongside separate penalties for late payment and interest running throughout.

The most important point is that the initial fixed penalty applies even if you owe no tax at all. People who file a nil return late are frequently surprised by it, and it is entirely avoidable by filing on time even when nothing is due.

What this calculator assumes

• An initial fixed penalty applies immediately after the filing deadline, regardless of whether tax is owed.
• Daily penalties accrue after three months, up to a cap.
• Further penalties apply at six and twelve months, based on the tax due.
• Late payment penalties are separate from late filing penalties.
• Interest runs on unpaid tax from the due date.

Limitations — what it does not cover

• Reasonable excuse, which can cancel penalties — serious illness, bereavement, or a genuine service failure. It must be appealed within 30 days.
• Time to Pay arrangements, which can prevent late payment penalties if agreed before they arise — contacting HMRC early genuinely helps.
• Deliberate and concealed behaviour, penalised on a much harsher scale.
• The new points-based regime being phased in for MTD.
• Whether a return was required at all — if not, ask for the notice to be withdrawn.
• Payments on account, which have their own due dates.