The SA303 form is a document that you can fill in and send to HMRC if you’re self-employed and want to reduce your Payment on Account.
You can also use the online Self Assessment service if you don’t want to deal with printing and sending it by post.
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Example of using the SA303 to reduce your Payment on Account:
You earned £30,000 in the 2024/25 tax year, all from self-employment
This is your first Self Assessment tax return
By January 31st, 2026, you need to pay £4,272 in Income Tax and National Insurance
You also need to pay an advance payment of 50% towards next year’s tax – that’s £2,136. This is called Payment on Account
By July 31st, 2026, you need to pay the rest of 50% – another £2,136. This is called a Balancing Payment
But let’s say that you know you’ll earn less this year – only £20,000. You can ask HMRC to reduce your Payment on Account through an SA303
However, you don’t actually need to file an SA303 – HMRC will automatically give you a refund if you overpaid through your Payment on Account
