Part of our complete guide to Self Assessment.
Two penalties, not one
HMRC treats "filing your return" and "paying your tax" as two entirely separate obligations, each with its own penalty regime. It's possible to file on time but pay late (and get hit with payment penalties and interest), or to pay on time but file late (and get hit with filing penalties despite owing nothing). Most people assume one deadline covers both, it doesn't.
Late filing penalties
These apply the moment your return is late, regardless of whether you owe any tax at all:
- 1 day late: automatic £100 penalty
- 3 months late: £10 per day for up to 90 days (up to £900 on top of the £100)
- 6 months late: a further £300 or 5% of the tax due, whichever is higher
- 12 months late: another £300 or 5% of the tax due, in serious cases up to 100% of the tax due
Use our late filing penalty calculator to see exactly how much a specific delay would cost you.
Key point: The £100 penalty applies even with a £0 tax bill. Filing a nil return late is still a late return.
Late payment penalties and interest
These are calculated differently, as a percentage of the tax actually outstanding, plus daily interest:
- Interest accrues daily on any unpaid balance from the payment deadline (31 January) until it's paid, at HMRC's prevailing late-payment rate (floats with the Bank of England base rate)
- 30 days late: a penalty of 5% of the unpaid tax
- 6 months late: a further 5% of the tax still unpaid
- 12 months late: another 5% of the tax still unpaid
Unlike filing penalties, payment penalties are proportional, a small outstanding balance means a small penalty. But interest keeps compounding the longer it's unpaid, so the cost of delay grows continuously, not just at the 30-day/6-month/12-month marks.
Why this distinction catches people out
The two most common mistakes we see:
- Filing late because the numbers aren't ready, assuming "no tax owed yet" means no penalty. It doesn't, the £100 fixed penalty is about the paperwork, not the money.
- Paying late while filing on time, assuming the filing deadline is the only one that matters. It isn't, 31 January is both the filing and payment deadline, and payment penalties run on their own clock from that date.
If you genuinely can't pay what's owed by 31 January, contact HMRC about a Time to Pay arrangement before the deadline, not after, it won't stop interest but it can reduce or avoid the percentage-based late payment penalties.
Already facing a penalty? Book a free consultation and we'll look at whether a reasonable excuse appeal applies, and make sure the current year doesn't repeat the problem.
Frequently asked questions
What's the penalty for filing one day late?
An automatic £100 penalty applies the moment you miss the deadline, even by one day, and even if you owe no tax at all. Use our late filing penalty calculator to see how it escalates from there.
Are late filing and late payment penalties the same thing?
No, they're entirely separate systems that can both apply at once. Filing late triggers fixed and daily penalties regardless of whether tax is owed. Paying late triggers interest plus separate percentage-based penalties, calculated on the amount still outstanding.
Can penalties be appealed?
Yes, if you have a "reasonable excuse", such as serious illness, bereavement, or a genuine technical failure, you can appeal within 30 days of the penalty notice. Being busy or forgetting is not considered reasonable.
Does interest keep running even if I appeal a penalty?
Interest on unpaid tax itself continues to accrue daily regardless of any penalty appeal, appealing a penalty doesn't pause interest on the underlying tax debt.