Tax overpayments and underpayments

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1. If you’ve not paid the right amount of tax

If you’ve paid too much or too little tax by the end of the tax year (5 April), HM Revenue and Customs (HMRC) will send you either:

  • a tax calculation letter (also known as a P800)
  • a Simple Assessment letter

This will tell you how to get a refund or pay tax you owe.

This guide is also available in Welsh (Cymraeg).

You’ll only get a letter if:

  • you are employed
  • you get a pension

If you’re registered for Self Assessment, your bill will be adjusted automatically if you’ve underpaid or overpaid tax. You will not get a tax calculation letter or a Simple Assessment letter.

When letters are sent

The letters are sent out between June and the end of November.

Why you might get a tax calculation letter

You might get a tax calculation letter if you either owe tax or are owed a refund because you:

  • were put on the wrong tax code, for example because HMRC had the wrong information about your income
  • finished one job, started a new one and were paid by both in the same month
  • started receiving a pension at work
  • received Employment and Support Allowance or Jobseeker’s Allowance

Why you might get a Simple Assessment letter

You might get a Simple Assessment letter if you:

  • owe tax that cannot be automatically taken out of your income
  • owe HMRC more than £3,000
  • have to pay tax on your State Pension

Find out how to pay your Simple Assessment bill.

You’ll need to pay the tax you owe by a certain deadline.

If you have not been sent a tax calculation letter or a Simple Assessment letter

If you think you have paid too much tax and HMRC have not sent you a tax calculation letter, find out how to claim a refund.

If you think you owe tax and you have not received a letter, contact HMRC.

2. If your tax calculation letter (P800) says you’re due a refund

Your tax calculation letter (also known as a P800) will tell you how you can get your refund.

If your tax calculation letter says you can claim online

To claim online, you’ll need your Government Gateway user ID and password.

If you do not have a Government Gateway account, you can create one.

To create a Government Gateway account, you’ll need your National Insurance number or postcode and 2 of the following:

  • a valid UK passport
  • a UK photocard driving licence issued by the DVLA (or DVA in Northern Ireland)
  • a payslip from the last 3 months or a P60 from your employer for the last tax year
  • details of a tax credit claim if you made one
  • details from a Self Assessment tax return if you made one
  • information held on your credit record if you have one (such as loans, credit cards or mortgages)

Claim now

You can also claim your refund through the HMRC app.

When you’ll get your refund

You’ll be sent the money within 5 working days - it’ll be in your UK account once your bank has processed the payment.

If you do not claim your refund online within 21 days, HM Revenue and Customs (HMRC) will send you a cheque. You’ll get this within 6 weeks of the date on your tax calculation letter.

If your tax calculation letter says you’ll get a cheque

Your tax calculation letter will tell you if HMRC will send you a cheque.

You do not need to contact HMRC to make a claim - you’ll automatically get the cheque by post.

When you’ll get your refund

You’ll get your cheque within 14 days of the date on your letter.

If you’re owed tax from more than one year, you’ll get a single cheque for the entire amount.

3. If your tax calculation letter (P800) says you owe tax

HM Revenue and Customs (HMRC) will collect the tax you owe over the next year. This will happen automatically if you:

  • pay Income Tax through an employer or pension provider
  • earn enough income over your Personal Allowance to cover the underpayment
  • owe less than £3,000

HMRC will write to you about how you can pay if they cannot collect the money this way.