The short answer
What are payments on account?
They are advance payments towards your next Self Assessment bill. Each one is usually half of your last bill and they are due by 31 January and 31 July. In January you also pay any balance for the year just ended, which is why the first January bill is often much bigger than people expect.
Who has to make them?
You have to make them unless your last Self Assessment bill was under £1,000, or more than 80% of your tax was already paid at source, for example through your tax code. They cover Income Tax and Class 4 National Insurance. Anything you owe for Capital Gains Tax or student loans is paid with the balancing payment instead.
What does a first-year January bill look like?
Say your first tax bill is £6,000 and you have made no payments on account. By 31 January you pay the £6,000 for that year plus a first payment on account of £3,000 for the current year: £9,000 in one go. A second payment of £3,000 follows on 31 July. Setting money aside each month makes this much easier.
Can I reduce my payments on account?
Yes, if you expect this year's bill to be lower, for example because your profit has fallen or more tax is being taken at source. You can ask HMRC to reduce them in your online account or by sending form SA303. Only reduce to a figure you can justify: if the final bill turns out higher, HMRC charges interest on the difference from the original due dates.
Are you a landlord?
Rental profit often decides whether payments on account apply. Use the rental income tax calculator to estimate this year's bill, including the new property rates from April 2027.