January gets all the attention. The 31 January deadline is famous enough that even people who have never filed a tax return know about it. But Self Assessment has a second, much quieter deadline every summer — and this year it falls on Friday 31 July 2026.
That is the date the second payment on account for the 2025-26 tax year is due. Miss it and HMRC starts charging interest from the very next day. Yet because it arrives in the middle of summer, with no January-style publicity, it is one of the most commonly forgotten dates in the tax calendar.
Who Has to Pay?
Payments on account apply if your last Self Assessment bill was more than £1,000, unless more than 80% of the tax you owe is collected at source — for example through a PAYE tax code. In practice that catches:
- sole traders whose January bill came in above £1,000
- landlords with meaningful rental profits
- anyone whose side income has grown beyond hobby scale
Many CIS subcontractors escape payments on account because tax is already deducted from their pay before it arrives — but not all do, so it is worth checking your HMRC account rather than assuming.
How the Amount Is Worked Out
Each payment on account is half of your previous year’s income tax and Class 4 National Insurance bill. The first half was due on 31 January; the second is due on 31 July. If your actual 2025-26 bill turns out higher, you pay the difference as a balancing payment next January. If it turns out lower, the difference is refunded or set against the next bill.
The system runs on one big assumption: that this year looks like last year. That assumption is exactly what causes trouble when income changes.
If Your Income Has Dropped, You Can Reduce It
If you know 2025-26 profits are lower than the year before — fewer jobs, a slow patch, time off — you can apply to reduce your payments on account, either through your HMRC online account or on form SA303. But reduce them below what you genuinely owe and HMRC charges interest on the shortfall, backdated to the original due date. Base the claim on real figures, not optimism.
Better Still: File Early and Know for Certain
You have been able to file your 2025-26 return since 6 April. File before 31 July and the guesswork disappears: your actual bill replaces the estimate, so the July payment adjusts to what you really owe — and any overpayment from January comes back sooner. Filing early does not mean paying the January balance early; that deadline stays put.
What If You Cannot Pay?
Do not ignore the deadline and hope. HMRC’s Time to Pay service lets many Self Assessment taxpayers spread what they owe over instalments, and it can often be set up online without speaking to anyone. Interest still applies, but an agreed plan stops the situation escalating — and arranging it before the deadline is always better than after.
The Bottom Line
The 31 July payment is only frightening when it arrives as a surprise. Know whether it applies to you, check the figure against how this year is actually going, and it becomes just another planned payment.
123Tax keeps that running picture for you: send income and receipts over WhatsApp as they happen and you always know roughly where the year stands — so summer deadlines are a number you planned for, not a shock in the post.