Tax Calculator

Self Assessment Filing Deadline & Penalty Calculator 2025/26

Miss the Self Assessment deadline and penalties mount quickly — £100 immediately, then £10/day, then percentage surcharges. Calculate exactly what HMRC will charge you and whether there is still time to reduce the damage.

Your Situation

Penalties & Interest

Total HMRC charges
£0
Filing + payment penalties
Immediate late filing penalty
£100
Daily penalties (after 3 months)
£0
6-month surcharge (5%)
£0
12-month surcharge (5%)
£0
Late payment penalty (30 days)
£0
Late payment interest (approx)
£0
Total additional charges
£0

Self Assessment Deadlines — Key Dates for 2024/25

Self Assessment is the system through which HMRC collects Income Tax from people whose tax is not deducted automatically through PAYE. The 2024/25 tax year ran from 6 April 2024 to 5 April 2025. The key deadlines are:

  • 5 October 2025: Register for Self Assessment if you have not previously filed (and need to report 2024/25 income)
  • 31 October 2025: Deadline for paper Self Assessment tax returns for 2024/25
  • 31 January 2026: Deadline for online Self Assessment tax returns for 2024/25 — and deadline to pay any tax owed
  • 31 July 2026: Deadline for second payment on account (if applicable)

Missing the 31 January deadline triggers automatic penalties that escalate over time. Even if you cannot pay the tax, you should still file the return — the filing penalties are separate from, and in addition to, the late payment penalties.

The Self Assessment Penalty Regime — How Penalties Escalate

HMRC's penalty regime for late Self Assessment returns is designed to apply increasing pressure over time:

Immediate Penalty — Day 1

The moment your return is one day late past the 31 January deadline, a fixed £100 penalty applies automatically. This applies regardless of whether you owe any tax — even a nil return filed late attracts the £100 penalty.

Daily Penalties — 3 Months Late

If the return remains unfiled after 3 months (1 May for the 31 January deadline), HMRC can charge £10 for each day the return remains outstanding, up to a maximum of 90 days (£900 maximum). HMRC issues these penalties through a penalty notice — they are not automatic — but once issued, each day's penalty is difficult to appeal.

Six-Month Surcharge

At 6 months late, an additional penalty of the higher of £300 or 5% of the tax due is charged. This means the 6-month surcharge can be substantial for larger tax bills — 5% of £20,000 = £1,000.

Twelve-Month Surcharge

At 12 months, another penalty of the higher of £300 or 5% of the tax due is charged. In cases where HMRC believes tax has been deliberately withheld, penalties of up to 100% of the tax can be charged at this stage.

Late Payment Penalties

Separate from the late filing penalties, HMRC also charges penalties for late payment of the tax owed:

  • 30 days late: 5% of unpaid tax
  • 6 months late: A further 5% of unpaid tax
  • 12 months late: A further 5% of unpaid tax

These are in addition to the daily interest charged on unpaid tax. The interest rate is set at the Bank of England base rate plus 2.5 percentage points — currently around 7.5% per annum. Interest runs from the date payment was due (31 January) to the date it is paid.

Reasonable Excuse — How to Appeal Penalties

HMRC will waive penalties where you have a "reasonable excuse" — a genuine inability to file or pay on time due to circumstances outside your control. HMRC accepts various reasonable excuses including: serious illness of you or a close relative, bereavement of a close relative close to the deadline, fire or flood destroying records, HMRC errors causing delay, or technical failures of HMRC's own systems.

What HMRC does NOT accept as a reasonable excuse: not knowing about the deadline (ignorance of the law), relying on someone else who failed to file on your behalf (e.g. an accountant), or having insufficient funds to pay (though this can be a mitigating factor in reducing penalties). To appeal, complete form SA370 online through your government gateway account, or write to HMRC setting out your reasonable excuse.

Time to Pay Arrangements

If you cannot pay your Self Assessment bill in full by 31 January, you can contact HMRC to set up a "Time to Pay" (TTP) arrangement — a payment plan spread over a period of months. Setting up a TTP before the deadline does not prevent the automatic late payment penalties from triggering, but HMRC will suspend further penalties while you keep to the arrangement. TTP can often be set up online through your government gateway account for tax debts up to £30,000.

Do I need to do Self Assessment?+
You need to do Self Assessment if you are self-employed with income over £1,000, a company director, a higher-rate taxpayer with untaxed income, have rental income over £2,500, or if your income (or your partner's) exceeds £60,000 and you claim Child Benefit. HMRC will usually notify you if you need to file, but not always — it is your responsibility to register if you need to.
What if I file a return but cannot pay the tax?+
File the return on time regardless — the filing penalty is separate from the payment penalty. If you cannot pay, contact HMRC before the 31 January deadline to discuss a Time to Pay arrangement. Filing on time and paying late is much better than doing both late. Interest will still accrue on the unpaid amount, but you avoid the avoidable filing penalties.
What are payments on account?+
Payments on account are advance payments towards your next tax bill, due on 31 January and 31 July. They are required if your Self Assessment tax bill is more than £1,000 (and less than 80% was collected at source through PAYE). Each payment on account is half your previous year's tax bill. If you think your income will be lower in the current year, you can apply to reduce your payments on account.