Why your first Self Assessment payment can be bigger than your tax bill

Annual liability is tax due for the income and other relevant facts of a tax year. A balancing payment is the amount left after tax credits and previous advances. A payment on account is an advance towards another year.

An advance changes when cash leaves your account; it is not an extra tax rate. Later, that advance is credited to the year it belongs to. Student-loan and Capital Gains Tax amounts can be part of a balancing payment without becoming part of the ordinary advance calculation.

Under the current rules, payments on account normally apply unless the previous relevant tax bill was less than £1,000 or more than 80% was collected outside Self Assessment, for example through PAYE. Class 4 NI is included in the relevant liability.

Each advance is usually half the relevant previous-year amount, after the applicable credits. The dates are normally 31 January and 31 July. A PAYE job can therefore change whether advances apply, but having a job does not automatically remove them.

Use HMRC’s statement for the actual amounts and allocations. The calculator illustrates the supported standard position; it does not move money or amend an HMRC demand.

Assume the £50,000 sole-trader-profit example for England in 2026/27, with no other income, reliefs, loans or tax credits. Income Tax and Class 4 total £9,731.80. No advances have been paid.

The £9,731.80 of advances belongs to 2027/28. It must not be counted as another £9,731.80 tax charge on 2026/27 profit.

Compare the final liability for that year with the advances and other credits. If the final bill is higher, the difference is a balancing payment; if lower, there may be a credit or repayment after HMRC reconciles the account.

For example, a £10,500 relevant liability after £9,731.80 advances leaves £768.20, before any separate loan, gains or other adjustments. The next January may also contain a new first advance. Read the tax-year label beside each line rather than adding every transaction on the statement as if it were still outstanding.

If you expect the relevant liability to be lower, you can ask HMRC to reduce payments on account online or using SA303. Base the request on a defensible estimate and update it when the facts change.

Reducing too far can mean interest on the shortfall. An uncertain future drop in income is not the same as a confirmed lower bill. Keep the calculation and evidence behind the estimate. If affordability is the problem rather than the liability, discuss a payment arrangement with HMRC.

Allocate expected receipts once across business costs, living costs and tax reserves. A payment calendar helps show whether the money will be available before each deadline. Repeatedly using a tax reserve for ordinary bills can create a shortfall even where annual profit looks adequate.

HMRC announced a move to smaller, more regular payments from April 2029, but had not fixed the payment frequency in its October 2026 factsheet. The January/July rules above remain the current model. Check the official transition details before planning the 2029/30 cycle.