YF AccountingLast updated: 13 August 2026
6 min read
You can file your 2025/26 Self Assessment tax return right now, and filing early does not mean paying early: whatever you owe is still not due until 31 January 2027. HMRC has been accepting 2025/26 returns since 6 April 2026, so the window has already been open for months.
Most people wait anyway. January arrives, the paperwork is missing, the accountant is booked up and HMRC’s phone lines are jammed. Filing in August instead costs nothing, moves none of your payment deadlines and buys you five months of breathing room. Here is what you actually gain.
When can you file, and when must you?
The 2025/26 tax year ended on 5 April 2026, and you have been able to send your return online any time since 6 April 2026. The deadlines at the other end are fixed:
| Date | What it means |
|---|---|
| 5 October 2026 | Register for Self Assessment if you have never filed before, or reactivate an old record |
| 31 October 2026 | Deadline for paper returns for 2025/26 |
| 30 December 2026 | File online by this date if you want a bill under £3,000 collected through your PAYE tax code |
| 31 January 2027 | Online filing deadline, and the day your 2025/26 tax is due |
| 31 July 2027 | Second 2026/27 payment on account, if payments on account apply to you |
Miss 31 January and there is an automatic £100 penalty, even if you owe nothing or are due a refund. If you are not sure whether you need to file at all, start with our guide on who needs to file a tax return.
Six good reasons to file early
1. You find out what you owe months in advance
Submit in August and HMRC calculates your bill straight away, but nothing is collected until 31 January 2027. If the bill turns out to be £4,000, you know from August that putting aside roughly £670 a month will cover it. Find out the same number in the second week of January and your options look very different.
2. Refunds come back sooner
If you overpaid tax in 2025/26, perhaps through PAYE, CIS deductions or payments on account that turned out too high, that money sits with HMRC until you file. File early and the overpayment shows on your calculation and can be claimed straight away. One wrinkle worth knowing: HMRC may offset a refund against a payment on account falling due within the next 45 days rather than repaying it to you.
3. You may be able to pay through your tax code
If you owe less than £3,000, already pay tax through PAYE (as an employee or on a company pension) and file online by 30 December 2026, HMRC will normally collect the bill through your tax code, spread across twelve months of salary or pension deductions rather than taken as one lump sum. There are limits: you need enough PAYE income for the deductions to work, and making a part payment to bring a larger bill under £3,000 does not qualify. Miss 30 December and the option is gone for the year.
4. Money tight? You get more options, earlier
Once the return is in and the bill is confirmed, you can set up a Budget Payment Plan, a Direct Debit that puts a weekly or monthly amount towards the bill before it falls due, provided your previous payments are up to date. And if you already know the full amount will not be there by 31 January, you can explore an instalment arrangement with HMRC with months in hand, rather than negotiating in deadline week.
5. If your income has dropped, you can cut January’s bill
Your payments on account for 2026/27 are based on your 2025/26 bill, half each on 31 January and 31 July 2027. If this year is shaping up quieter than last, filing early gives you the figures to judge whether to ask HMRC to reduce those payments, and the claim can go in well before the first one is collected. Reduce them too far and HMRC charges interest on the shortfall, so base the claim on real numbers. There is a full explanation in our payments on account guide.
6. January is the worst possible month for it
By January, accountants are full, HMRC call queues are at their longest and any snag has no slack left to absorb it: a lost UTR, a missing P60, an online account that will not activate. If you have never filed before, registration alone can take weeks because your UTR arrives by post, and the deadline to register for 2025/26 is 5 October 2026. Our step by step guide to registering for Self Assessment covers it. File in the summer and the inevitable snags cost you nothing.
What filing early does not change
Your payment deadlines stay exactly the same: 31 January 2027 for the 2025/26 balance, plus a first 2026/27 payment on account if they apply to you, then 31 July 2027 for the second one. You can still amend the return within 12 months of the 31 January deadline if something changes. And if part of your income is not final yet, you can file using provisional figures and correct them later, as long as you tell HMRC that is what you have done.
One more thing that does not change: Making Tax Digital. If you were brought into MTD for Income Tax from April 2026, the quarterly updates you now send relate to 2026/27. Your 2025/26 return is still filed the normal Self Assessment way. More on that in our MTD for Income Tax guide.
What to have in front of you
- Your UTR and Government Gateway sign in details
- P60, P45 or P11D if you were employed during the year
- Self-employment income and expense records
- Rental income and letting costs if you are a landlord
- Bank interest, dividend vouchers and other investment income
- Pension contributions and Gift Aid donations, which can reduce the bill
- Details of anything you sold that might trigger Capital Gains Tax
Frequently asked questions
If I file in August, do I have to pay straight away?
No. Filing and paying are separate. Your 2025/26 tax is due on 31 January 2027 whether you file in August 2026 or on deadline day. Filing early simply tells you the figure sooner, and if payments on account apply to you, those dates do not move either.
When is the deadline for the 2025/26 tax return?
Paper returns must reach HMRC by 31 October 2026 and online returns by 31 January 2027, which is also when any tax owed is due. File late and the £100 penalty applies automatically, even if you owe nothing at all.
Can HMRC collect the tax I owe through my wages?
Often, yes. If you owe less than £3,000, already pay tax through PAYE and file online by 30 December 2026, HMRC will usually collect the bill through your tax code in twelve equal instalments from April 2027. You need enough PAYE income for the deductions to work, and it is worth checking your calculation to confirm it has been set up.
What if I cannot afford my tax bill?
File anyway, and as early as you can: filing penalties are separate from the tax itself, and knowing the number early gives you options, from a Budget Payment Plan to an instalment arrangement with HMRC. If you would rather hand the whole thing over, our fixed fee Self Assessment service prepares, checks and files your return and deals with HMRC for you, and our Self Assessment guide covers the rest of the system.
Would rather not think about any of this again? YF Accounting files Self Assessment returns for directors, sole traders, landlords and higher earners on fixed fees, with one accountant handling everything and unlimited support included. Send your records over this summer and your return is done long before the rush. Book a free call and consider it sorted.
Founder of YF Accounting — a fixed-fee, fully digital accountancy practice in Manchester serving SMEs, sole traders and landlords across the UK. One point of contact, unlimited support, no surprise bills.
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Tax on Rental Income: What UK Landlords Pay in 2026/27This article is part of our Self Assessment guide. See the full topic for related reads.