UK payments on account calculator: what do I owe on 31 January and 31 July? Free, private

What do I owe HMRC on 31 January and 31 July?

Enter your Self Assessment bill (income tax plus Class 4 NIC) and what was already deducted at source. You get the balancing payment, both advance instalments for the next year, the cash to set aside, and whether a reduction claim would help.

A first read written from HMRC's published rules without a live lookup. Rules change; confirm the current text. Income tax and Class 4 NIC only. Not tax advice.

Tax year of the return you are filing

Income tax + Class 4 NIC for that year (£)

Already deducted at source, e.g. PAYE or CIS (£, optional)

Payments on account already made for that year (£, optional)

Other amounts due 31 January: CGT, student loan, child benefit charge (£, optional)

Expected income tax + Class 4 NIC next year (£, optional)

Fill in the figures, then click Work out my payments.

Result

Payment schedule

Date	What	Amount

What you must do

Step	What it means

What it does, and what it leaves to you

Covers: the balancing payment, the two advance instalments (each half of last year's relevant bill), the 31 January cash total, the £1,000 and 80% exemptions, and a reduction claim.
Gives: a dated payment schedule, a monthly set-aside figure and a checklist.
Not decided: how to compute your tax bill itself, Scottish bands, capital gains, student loan or child benefit charge amounts, interest and penalty figures, whether a reduction claim is justified, and anything that changed after this was written.

Common questions

What are payments on account?

Advance instalments towards next year's Self Assessment bill. Each is half of your last bill (income tax plus Class 4 NIC, after tax deducted at source), due on 31 January and 31 July.

Why is my first Self Assessment bill so big?

The 31 January bill carries two things: the balance for the year just ended and the first advance instalment for the next year. In the first year you have no instalments to set against the balance, so the total is about 150% of a normal year's tax. It is not extra tax; it is next year's tax paid early.

Who does not have to make payments on account?

Nobody pays them if last year's bill after tax deducted at source was under £1,000, or if more than 80% of your income tax and Class 4 NIC was collected at source, for example through PAYE.

Can I reduce my payments on account?

Yes, if you expect a lower bill for the new year you can claim to reduce them through your HMRC account or form SA303. It only changes timing: if you reduce too far, interest runs from the original due dates on the shortfall.

What happens if I miss a payment?

Interest runs from the due date and further penalties apply if the tax stays unpaid. Check the current rates on GOV.UK.

Is my data uploaded anywhere?

No. Everything is calculated in your browser and nothing is sent.