Self-Employment Tax: Register to Submit / Lesson 11 of 12
Deadlines, penalties and interest
A day late is £100. What comes after that is worse.
The short answer
- ✓ The £100 late filing penalty applies even when you owe no tax
- ✓ Late filing and late payment are penalised separately, and both can apply
- ✓ Filing and paying are both due on 31 January, along with the first payment on account
- ✓ If you cannot pay, file anyway and then arrange Time to Pay
The dates that matter
| Date | What is due |
|---|---|
| 5 April | Tax year ends |
| 5 October | Deadline to register if you started trading in the year just ended |
| 31 October | Paper return deadline |
| 31 January | Online return deadline, and payment deadline, and first payment on account |
| 31 July | Second payment on account |
Note how much lands on 31 January. Filing the return, paying the balance, and paying the first instalment towards next year all fall on the same day. Treating it as one deadline rather than three is how people end up paying part of what they owe and still incurring a penalty.
Late filing: how it escalates
1 day late £100 fixed, even if you owe nothing at all
3 months late £10 per day, for up to 90 days (up to £900)
6 months late 5% of the tax due, or £300 if greater
12 months late another 5% of the tax due, or £300 if greaterThese stack. A return that is a year late has accumulated the £100, the daily charges, and both percentage penalties, before any tax or interest is even considered.
The £100 is the part people find hardest to believe: it applies even when your tax bill is zero. The penalty is for not filing, not for not paying.
Late payment: a separate set of charges
Paying late is penalised separately from filing late, and both can apply at once.
| How late the payment is | Penalty |
|---|---|
| 30 days | 5% of the tax unpaid |
| 6 months | A further 5% |
| 12 months | A further 5% |
Interest also runs on the unpaid amount from the due date, and interest is not a penalty, so it is not waived even when a penalty is.
The bit HMRC does not spell out
Filing and paying are separate obligations, and if you cannot do both, file anyway. Filing costs nothing and stops the larger, faster-escalating penalty clock. If you then cannot pay, HMRC has a Time to Pay arrangement that lets many people spread the bill by instalment, and it is far easier to arrange when your return is already in and the amount is known.
People do the opposite. They cannot pay, so they avoid filing, and end up owing the tax, the interest, the late payment penalties and the late filing penalties. Filing on time when you are short of money is the single best decision available to you.
Reasonable excuse
Penalties can be appealed where there is a reasonable excuse: serious illness, a bereavement, a genuine service failure at HMRC's end. Being busy, finding it difficult, or relying on someone else to do it are explicitly not reasonable excuses. Appeal if you have a genuine reason, and do not count on it otherwise.
Common mistakes
- Not filing because you cannot pay. The most expensive mistake in this lesson.
- Assuming a nil return has no penalty. The £100 applies regardless of the tax due.
- Forgetting 31 July. It is a real deadline with real consequences.
- Expecting interest to be waived with a penalty. It is compensation, not a punishment, and is treated differently.
Try it on your own numbers
This is the same calculator as the full tool page, using 2026/27 rates.
Late Self Assessment
Estimate HMRC penalties and interest for a late Self Assessment return and payment.
Penalties stack as time passes. The timeline below shows how the total grows the longer you wait - file and pay as soon as you can.
Penalty milestones
- -
Estimate for individual Self Assessment. Daily penalties, interest and special cases vary - check gov.uk. Not advice.
Estimated penalties & interest
on top of of tax owed
- Late filing penalties
- Late payment penalties
- Interest (approx)
- Tax + penalties + interest
What this costs you
extra to pay
on top of your tax
Wait until you cross the next milestone and this estimate rises to .
File and pay as soon as possible - penalties and interest keep growing.
How the bill grows over time
Estimated extra cost (penalties and interest) for of tax owed, at each lateness stage.
| Lateness | Filing | Payment | Interest | Extra total |
|---|---|---|---|---|
Your current selection is highlighted. Figures are estimates and assume the tax stays unpaid throughout each stage.
Compare saved scenarios
| Scenario | Penalties + interest | Total to pay | |
|---|---|---|---|
Key takeaways
- ✓ The £100 late filing penalty applies even when you owe no tax
- ✓ Late filing and late payment are penalised separately, and both can apply
- ✓ Filing and paying are both due on 31 January, along with the first payment on account
- ✓ If you cannot pay, file anyway and then arrange Time to Pay
Check you have got it
3 quick questions. No score is kept, and you can change your mind.
1. You owe no tax at all, but file three weeks late. What happens?
2. You have filed on time but cannot afford to pay. What is the best move?
3. Which of these counts as a reasonable excuse for filing late?
Sources
Finished this lesson?
Mark it done and we will remember where you got to.
You are 11 lessons in. Want to keep your progress?
Right now your place is saved in this browser only. A free account keeps it across devices, unlocks the end-of-course exam and certificate, and gives you a personal action plan at the end. No card, no upsell.
