Hour 1 after the deadline
Missing the 31 January Self Assessment deadline triggers automatic penalties regardless of whether you owed any tax. This guide covers exactly what happens hour-by-hour and day-by-day after the deadline, what appeals are possible, and how to minimise damage if you've already missed it.
Hour 1 after the deadline
The £100 flat late-filing penalty is applied automatically the day after the deadline (2 February). No tax owed → still £100. The penalty appears on your HMRC account within days.
The balancing payment and any payment on account also become late — late-payment interest starts accruing from 1 February at HMRC's official rate (~7.75%).
Days 1-90: escalating penalties
Day 30 (2 March): if the tax remains unpaid, a 5% late-payment penalty is added on top of the £100 filing penalty and accruing interest.
Day 90 (2 May): daily £10 penalties start accruing (up to 90 days = £900 additional).
Day 180 (2 August): further 5% or £300 (whichever higher) late-filing penalty. Another 5% late-payment penalty triggers.
Day 365 (2 February next year): further 5% or £300. Further 5% late payment.
Cumulative worst-case for a £5,000 tax bill: £100 + £900 + 5% × 3 = £1,750+ interest, on top of the £5,000. Roughly 35% surcharge.
Damage limitation now
File immediately. Filing stops the daily-penalty accrual. Even if you can't pay, file the return.
Request Time to Pay via HMRC's online service. If you set it up before day 30, you avoid the 5% late-payment penalty. Interest still accrues.
Reasonable-excuse appeal: if you have grounds (serious illness, bereavement, HMRC error). Submit via online account or written appeal within 30 days of the penalty notice.
Worked example
You filed 17 March, paid 17 March. Penalties: £100 flat late-filing (from day 1). Late payment: 5% of £3,800 = £190 (triggered at day 30). Interest: £3,800 × 7.75% × 45/365 = ~£36. Total added to bill: £326. Total to pay: £4,126.
Reference table
| Days late | Filing penalty | Payment penalty | Cumulative on £5k tax |
|---|---|---|---|
| 1 | £100 | 0 | £100 |
| 30 | £100 | £250 (5%) | £350 + interest |
| 90 | £1,000 (£100+£900) | £250 | £1,250 + interest |
| 180 | £1,300 (+5%) | £500 (2×5%) | £1,800 + interest |
| 365 | £1,600 (+5%) | £750 (3×5%) | £2,350 + interest |
Missed-deadline damage-limitation checklist
- File the return today — stops daily penalty accrual
- Set up Time to Pay if cash-tight — call HMRC 0300 200 3822
- Pay as much as you can afford — interest reduces on remaining amount
- Consider reasonable-excuse appeal within 30 days if grounds exist
- Get an accountant if the situation is escalating
- Set a phone reminder for the next year's deadline
Yes — it's a flat penalty for late filing, not linked to tax owed.
Yes if you have a reasonable excuse. HMRC decides case-by-case. 'I forgot' is not a reasonable excuse; serious illness usually is.
No — HMRC doesn't hold a 'record' against you for future extensions. Each year is assessed independently.
In extreme cases, yes — Direct Recovery of Debts allows HMRC to take from bank accounts for large unpaid tax. Only used after multiple non-responses to correspondence.
Sign in to your personal tax account → Self Assessment → statement. Shows tax, penalties, interest and total balance owed.
Sources & official references
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This guide is general information based on UK rules for the 2025/26 tax year. It is not personal tax or legal advice. For decisions affecting your tax position or legal exposure, consult a qualified accountant or solicitor.