Tax Overpayments and Underpayments

Your Tax Calculation 

If you are employed or get a pension, HM Revenue and Customs (HMRC) checks whether you are paying the right amount of tax throughout the year. 

They may adjust your tax during the year if your circumstances change, for example if you get a pay rise or a company benefit (external link). 

If you have not paid the right amount at the end of the tax year, HMRC will post you a tax calculation. This can be a P800 or a Simple Assessment letter. 

Your tax calculation will show you how to get a refund or pay tax you owe.  

When you might get a P800  

You might get a P800 if you: 

  • 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 

You will not get a P800 if you are registered for Self Assessment (external link). Your bill will be adjusted automatically if you have underpaid or overpaid tax.  

P800s are sent out after the tax year ends on 5 April. You’ll normally get yours by the end of November.  

When 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 the State Pension 

You can pay your Simple Assessment bill online (external link)

Checking your Tax Calculation 

Your letter will show the income (external link) you should have paid tax on. This includes any income from pay, pensions, state benefits (external link), savings interest and employee benefits (external link)

Compare the figures with your records, for example your P60 (external link), bank statements or letters from the Department for Work and Pensions. If your state benefit was paid every 4 weeks, work out the total paid in a year by multiplying your regular payment by 13 (not 12).  

You may be able to use the HMRC tax checker (external link) to work out how much tax you should have paid. 

If you think your Tax Calculation is Wrong 

Contact HMRC (external link) if you think the amounts used in your letter are wrong, or HMRC did not act on information (external link) you gave them.  

You have 60 days to query your simple assessment in writing or by telephone. The details of how to do that will be mentioned in your Simple Assessment letter.  

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