UK Self Assessment Payment on Account Calculator

You have to make POAs if your previous Self Assessment income tax + Class 4 NIC, after deducting tax already collected at source, was £1,000 or more and less than 80% of that same income tax + Class 4 NIC figure was collected at source (PAYE, CIS, sub-contractor or pension deductions). Capital Gains Tax, Class 2 NIC and Student Loan repayments sit outside the 80% test as well as outside the POA base. A bill of exactly £1,000 does attract payments on account — the exemption applies only below £1,000.

The first POA is due 31 January during the tax year (alongside the balancing payment for the previous year). The second POA is due 31 July. The balancing payment for the current tax year is due the following 31 January.

Capital Gains Tax, Class 2 NIC and Student Loan repayments are excluded from the POA base and from the 80%-at-source test. They're added to the balancing payment instead. The POA is 50% of your prior-year income tax + Class 4 NIC, less any tax already deducted at source.

Yes. HMRC's SAM1010 lists "Underpayment transferred to PAYE" among the amounts deducted in arriving at the payment on account figure, and TMA 1970 s59A(8) counts tax due for a year that is coded out in a later year as tax deducted at source. So it comes off the POA base and counts towards the 80%-at-source test — which can remove the payments on account altogether. The same subsection works the other way too: tax taken through last year's code that was settling an earlier year's underpayment is not deducted at source for last year, so it is added back.

Yes — file form SA303 (or reduce online in your Self Assessment account) if you expect your current-year profits to be lower. Warning: if you reduce too far, HMRC charges interest on the shortfall from the original due date, so base the claim on a realistic forecast.

POAs only attract daily interest (Bank of England base rate + 4% since 6 April 2025). The 5% late-payment penalties apply to the balancing payment only, charged at 30 days, 6 months and 12 months after the 31 January due date.