Tax overpayments and underpayments

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1. If you鈥檝e not paid the right amount of tax

If you鈥檝e 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鈥檒l only get a letter if:

  • you are employed
  • you get a pension

If you鈥檙e registered for Self Assessment, your bill will be adjusted automatically if you鈥檝e 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聽between June and March of the following tax year.

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鈥檚 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 拢3,000
  • have to pay tax on your State Pension

Find out how to pay your Simple Assessment bill.

You鈥檒l 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鈥檙e 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

You can claim using the online bank transfer service or request a cheque online. You鈥檒l need:

  • the reference number from your P800 letter
  • your National Insurance number

If you want your refund through a bank transfer, you鈥檒l need to have a UK bank account.

Other ways to claim

You can also claim a refund:

When you鈥檒l get your refund

You鈥檒l be sent the money within:

  • 5 working days if you鈥檝e claimed online
  • 6 weeks if you鈥檝e asked HMRC to send you a cheque

If your tax calculation letter says you鈥檒l 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鈥檒l automatically get the cheque by post.

When you鈥檒l get your refund

You鈥檒l get your cheque within 14 days of the date on your letter.

If you鈥檙e owed tax from more than one year, you鈥檒l 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 拢3,000

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

If you think your tax calculation is wrong

If you think the amounts used in your calculation are wrong, contact HMRC.

You鈥檒l need to tell HMRC which amounts you think are incorrect and what they should be.

What happens next

If HMRC agrees that your tax calculation was wrong, you鈥檒l be sent a new calculation.

If they disagree, HMRC will contact you to explain why.