In certain scenarios, as detailed in our article for When do I make payments on account? HMRC expect taxpayers to contribute Payments on Account towards the overall liability via payments being made in advance on 31st January and 31st July. In order to declare any payments made on your returns, please use the below locations: 

SA100 tax return:

SimpleStep mode: Working out your tax > Payments on account for 2025-26
HMRC Forms mode: Tax Calculation > Payments on account > Box 10 and 11 (bottom of the page)

SA900 tax return
HMRC Forms mode: Payments on account

If you would like more information on any values calculated within TaxCalc, please see the link to How are Payments on Account calculated