HMRC always recalculate the tax that someone has paid once a tax year has ended. If for some reason it turns out someone was on the wrong tax code and they owe additional tax of £3,000 or more, then they will issue a simple assessment.
What is an HMRC Simple Assessment?
If you are employed or receive a pension, then you may receive a simple assessment if HMRC finds that you have underpaid your tax by more than £3,000. If you owe less than £3,000 you’ll receive a P800 letter instead with different instructions on what to do. After the end of a tax year*, HMRC reviews the information they have on file about your income from things like employment, pensions and benefits in kind. They then compare this to the amount of tax you have paid using paperwork like P60s and P45s.
If they find that you have underpaid your tax by more than £3,000 they will send you a Simple Assessment, normally by November, which includes a tax calculation and details of how you can pay your bill.
* the tax year starts 6 April and ends 5 April each year
What to Do If Your Simple Assessment is Wrong
If you disagree with the tax calculation HMRC sends you then you 60 days to respond to HMRC in writing or by phone. Once 60 days have passed you’ll need to settle your tax bill.
When Do Your Need to Pay Your Tax to HMRC
You’ll need to pay your simple assessment tax by the 31 January following the end of the tax year that you owe money.
So if you received an assessment for the tax year 2019/2020, you’ll need to settle any tax you owe by 31 January 2021.
How to Pay Your Simple Assessment Tax
You can pay your tax bill by going online, bank transfer or cheque.
If you chose to do a transfer then you’ll need to use your Charge Reference Number as your payment reference so it gets allocated correctly. HMRC’s bank details are account number: 12001020 and sort code: 08 32 10.
If you prefer to send a cheque, then you’ll need to make it out to HM Revenue and Customs only, write your charge reference number on the back and post it to: