Self Assessment deadlines
Register by 5 October, file a paper return by 31 October or online by 31 January, and pay what you owe by 31 January. A second payment on account, where you make them, falls on 31 July. Missing the filing date costs £100 immediately, charged even when you owe no tax.
Four dates, and the two that share 31 January are the ones that catch people: the return and the money are due the same day, and they are penalised separately.
Which year you are filing
Tax years run 6 April to 5 April and the return arrives long after the year has closed. A return due on 31 January 2027 covers 6 April 2025 to 5 April 2026 — nearly ten months in the past by the time it is due.
That gap is why records get lost. The receipt you cannot place in January was for something you did eighteen months earlier.
The dates in order
- 5 October — register if this is your first year in Self Assessment. Leave it and the UTR may not arrive in time to file.
- 31 October — paper returns. Three months earlier than the online date, which surprises people who prefer paper.
- 31 January — the online return, the balancing payment for the year, and the first payment on account for the next one. Three obligations, one date.
- 31 July — the second payment on account, where they apply. See paying your bill.
Two penalty regimes, running at once
Filing late and paying late are punished separately. Do both and you pay both.
Filing late
| How late | Penalty |
|---|---|
| The day after | £100, charged even when you owe no tax |
| 3 months late | £10 a day, up to 90 days — £900 |
| 6 months | 5% of the tax due or £300, whichever is greater |
| 12 months | another 5% or £300 |
Paying late
5% of the tax still unpaid at 30 days, again at 6 months, and again at 12 months. Interest runs from the due date regardless, and has no reasonable-excuse defence.
Which produces the outcome nobody expects: file on time, pay a month late, and there is still a bill. The two dates being identical makes it easy to assume that meeting one covers the other.
Get it filed before the date, not after it
Send us the year's records and we will tell you the figure well before January — so the payment is budgeted rather than discovered. Fixed fee agreed in writing after a free assessment.
Ask on WhatsAppOr send an email
Free assessment first. If there is work to do, you get a fixed quote in writing before anything starts.
Why we push clients to file in the spring
The return can be filed from 6 April, ten months before it is due, and nothing about filing early moves the payment date. What it changes is everything else: you know the number in April instead of January, refunds arrive before the queue forms, and anything missing can still be found while people remember it.
The January rush exists because of a deadline, not because of the work. The work was possible in April.
Questions people ask
When is the Self Assessment deadline?
31 January for an online return, 31 October on paper. The tax is due on 31 January too — the same date, which is why people who file in time still get a penalty for paying late.
Which tax year am I filing for?
The one that ended on 5 April. Returns due on 31 January 2027 cover 6 April 2025 to 5 April 2026 — the 2025/26 year. Filing "this year's" return is one of the more common confusions, and it produces returns for a year that has not finished.
What happens the day after the deadline?
£100, charged even when you owe no tax. Then £10 a day from 3 months late (up to 90 days — £900), then 5% of the tax due or £300, whichever is greater at six months, then another 5% or £300 at twelve.
Are the payment penalties separate?
Yes, and they run alongside: 5% of the tax still unpaid at 30 days, again at 6 months, and again at 12 months. Interest runs from the due date regardless, and has no reasonable-excuse defence. A return filed on time but paid late still attracts them.
Can I appeal a late filing penalty?
Yes, normally within 30 days, with a reasonable excuse — serious illness, bereavement, a genuine HMRC service failure. File the return first: the penalty stops growing when it lands, and an appeal made with the return still missing rarely succeeds.
Is there any benefit to filing early?
Several. You learn the bill months before you have to pay it, refunds arrive while the queue is short, and if something is missing you have time to find it. Filing early does not mean paying early — the payment date is unchanged.
Figures are for the tax year shown and change every April. They are general information, not advice — we check the current position for your circumstances before anything is filed.
Reviewed 19 October 2026.
Part of our work on self-employment and self assessment — if you want someone to take it off your hands, start with our Self Assessment accountant page.