Self Assessment deadlines and payments on account, explained

The key dates

The tax year runs from 6 April to 5 April. For the 2025–26 tax year, the main deadlines are:

• 5 October 2026, tell HMRC you need to file, if you have not done so before.
• 31 October 2026, paper tax returns.
• 31 January 2027, online tax returns, and payment of any tax still owed for 2025–26 plus the first payment on account for 2026–27.
• 31 July 2027, second payment on account for 2026–27.

How payments on account work

Unless last year’s Self Assessment bill was under £1,000, or more than 80% of the tax you owed was collected before Self Assessment (for example through PAYE), you make two advance payments towards the next year’s bill. Each payment on account is half of the previous year’s liability, due on 31 January and 31 July. Any balance is then paid by the following 31 January.

If your income has fallen, you can apply to reduce payments on account, but interest is charged if the reduction turns out to be too large.

Filing or paying late

Under the standard Self Assessment rules, a late tax return attracts an initial £100 penalty, even if you owe no tax. After three months, daily penalties of £10 apply for up to 90 days; further penalties follow at six and twelve months. Separately, late payment penalties of 5% of the unpaid tax are charged at 30 days, six months and twelve months, and interest runs on unpaid tax.

If you are in MTD for Income Tax, late-submission penalties use a points system instead.

Why filing early helps

Filing well before January gives you time to plan for the payment, spot problems while there is still time to fix them, and receive any repayment sooner. It also avoids the busiest weeks of the year for accountants and HMRC alike.

Anewthing can prepare and file your return, check your payments on account and look for reliefs you may be missing. Start an enquiry.