Payments on Account Explained: Why Your Tax Bill Is Bigger Than Expected

If your first Self Assessment bill came in far higher than you expected, payments on account are almost certainly why. They’re not extra tax — but they are a cash-flow shock if you don’t see them coming. Here’s how they work.

What are payments on account?

Payments on account are advance instalments towards your next year’s tax bill. Rather than waiting for you to file and pay in one lump, HMRC asks you to pay ahead based on your current bill.

You make two:

• 31 January — 50% of next year’s estimated tax (alongside your balancing payment for the year just gone)
• 31 July — the other 50%

The estimate is simply based on this year’s tax bill.

Why your first bill feels brutal

Here’s the trap that catches every first-time filer. The first time payments on account kick in, on 31 January you pay:

• Your actual tax bill for the year just ended (your “balancing payment”), plus
• The first payment on account (50%) towards next year

That’s effectively 150% of one year’s tax in a single payment. It’s not a mistake or extra tax — you’re settling this year and getting ahead on next year — but it’s a serious cash-flow hit if nobody warned you. Our Self Assessment calculator helps you see the numbers coming.

When they apply (and don’t)

You make payments on account if:

• Your last Self Assessment bill was over £1,000, and
• Less than 80% of your tax was collected at source (e.g. via PAYE)

If your bill is under £1,000, or most of your tax is already deducted through PAYE, you generally don’t make them.

Reducing your payments on account

If you expect lower income next year — a quieter year, or you’ve stopped a side business — you can apply to reduce your payments on account to a more realistic figure, easing the cash-flow burden.

But take care: if you reduce them too far and end up owing more, HMRC charges interest on the shortfall. Any reduction should be based on a genuine, realistic estimate — not just a wish to pay less now.

The key is knowing it’s coming

The shock of payments on account isn’t really the money — it’s the surprise. When you know your January bill will include a payment on account, you can set the cash aside and plan for it. When you don’t, it’s a nasty January.

Our Self Assessment service calculates your bill — including any payments on account — well in advance, so you’re never caught out, and reviews whether a reduction is appropriate. Pair it with the deadlines and penalties and you’ll never face a January surprise again.