Why it matters
They help explain why a January payment can include more than the tax for the year just completed. The usual instalment dates are 31 January and 31 July, but eligibility and exclusions need checking. Plan from the actual calculation and statement rather than assuming that half of every tax figure is always payable.
A practical example
If a relevant £4,000 bill creates payments on account and none were previously made, January could include the £4,000 bill and a £2,000 advance for the next year. Another £2,000 would normally be due in July. This illustration excludes other liabilities and adjustments.
A common misunderstanding
An advance payment is not an extra tax rate. It is credited towards the relevant later bill. Reducing payments can be appropriate when the liability will fall, but an excessive reduction may lead to interest. Keep the estimate supporting any reduction.
Sources & further reading
General information for UK readers, updated 3 November 2026. Examples are illustrative. Tax treatment depends on the facts and current rules; seek advice before making a decision.