What payments on account are
HMRC describes payments on account as payments towards your next tax bill, including Class 4 National Insurance if you are self-employed. They spread the cost by splitting that bill into two instalments. Each payment is usually half of the tax you owed last year. They are due by midnight on 31 January and 31 July.
You must make the two payments unless either of two official tests applies: the amount of tax you owed last year was less than £1,000, or last year you paid more than 80% of the tax you owed outside Self Assessment — for example through a tax code, or because a bank had already deducted tax on savings interest. “Less than £1,000” means £999.99 or less on this arithmetic; at exactly £1,000 the first test does not apply. “More than 80%” means a share strictly above 80%; at exactly 80% this tool still treats payments on account as due.
January and July
If you did not make payments on account last year — a first-time return is a common example — you usually pay the full amount of last year’s tax calculation and the first payment on account towards the next bill, both by midnight on 31 January, and the second payment on account on 31 July. If last year’s relevant tax was £3,000, that pattern is a £3,000 balancing amount plus a £1,500 first instalment (£4,500 in January) and a £1,500 second instalment in July. Those are our example numbers, arranged in the same structure as the examples on the official payments-on-account page.
If you already made payments on account towards last year’s bill, the January total is the balancing payment (last year’s tax minus what you have already paid on account) plus the first instalment towards the next year. In an example where last year’s bill is £3,000 and two earlier instalments of £900 have already been paid, the balancing payment is £1,200, January is £2,700 and July is still £1,500. Change the boxes to your own figures.
Capital Gains Tax and student loan repayments are not built into payments on account. The official page says they go on the 31 January balancing payment. If your income this year will be lower, you can ask HMRC to reduce payments on account online or by sending form SA303. If you reduce them too far, interest may be charged on the difference. This calculator does not compute that interest in pounds; use the official interest-rates list if you need the current rate.
What to enter
Use the Income Tax and Class 4 figure from last year’s calculation as “relevant tax”. Do not include Capital Gains Tax or a student loan repayment in that box if you can separate them. The optional “paid outside Self Assessment” box is only for the 80% test. The optional “already paid on account” box is only for the balancing-payment arithmetic. Your online account or Self Assessment statement remains the official source for the amounts HMRC expects.
The second payment on account that relates to the 2026/27 year is due on 31 July 2027. For the 2025/26 bill you are settling now, the online filing and payment deadline is 31 January 2027, which can include both the balancing payment and the first payment on account towards 2026/27.