Payments on account
Payments on account are two advance payments towards your next tax bill. Follow the figures through 31 January and 31 July.
This path is practice in how the records and the sums work. It is not tax advice. Any rate or allowance in a question is an example for that question, so check GOV.UK for the current figures.
Your tax bill for a year is the tax worked out from that year's return. A payment on account is an advance payment towards the next year's bill.
HMRC asks for payments on account once your bill is above a limit. The limit and the exceptions are on GOV.UK.
There are two, due on 31 January and 31 July. In this room each one is half of the bill for the year before.
The first is due on the same 31 January as the bill it is based on. So in the first year there is more to pay that day than the bill alone.