Late Tax Return Penalty Calculator
Estimate HMRC penalties for filing your Self Assessment late. Penalties stack — file as soon as possible to stop the clock.
How late?
Late return? Stop the clock today
Half our clients first contact us with HMRC chasing. We file fast and argue penalties down where there's a reasonable excuse.
How HMRC penalties work
HMRC has separate penalty regimes for filing late and paying late. Both apply if you do both. Penalties stack quickly — a return left for a year can easily cost £1,600+ before any tax is paid.
The good news: HMRC accepts "reasonable excuse" arguments far more often than people think. Serious illness, bereavement, IT failures, postal delays — all viable. We argue these as part of our standard filing service.
Self Assessment late filing penalties
| How late | Penalty |
|---|---|
| 1 day late | £100 instant fine (even if £0 owed) |
| 3+ months late | +£10/day for next 90 days (max £900) |
| 6+ months late | + greater of £300 or 5% of tax |
| 12+ months late | + another £300 or 5% |
Late payment penalties stack on top: 5% of unpaid tax at 30 days late, another 5% at 6 months, another 5% at 12 months. Plus interest at HMRC's official rate (~7.75%).
Key Self Assessment deadlines
- 5 October following tax year end — register if first time
- 31 October — paper return deadline (rarely used)
- 31 January — online return + balancing payment + first PoA
- 31 July — second Payment on Account
Reduce or appeal penalties
- File now — even today's £100 penalty stops the £10/day clock from starting
- Reasonable excuse appeal via SA370 form — works for genuine cases
- Time-to-Pay arrangement — agree a payment plan before the surcharge dates to avoid penalties
- Disclosure of past errors — coming forward voluntarily reduces penalties significantly
What this calculator does and doesn't do
- £100 instant penalty for any late filing (even £0 owed)
- £10/day from day 91, capped at £900 (over the next 90 days)
- At 6 months: greater of £300 or 5% of tax owed
- At 12 months: another £300 or 5% of tax owed
- Late payment penalty: 5% at 30 days, another 5% at 6 months, another 5% at 12 months
- Plus interest at HMRC's official rate (~7.75%)
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