Tax overpayments and underpayments
If your tax calculation letter (P800) says you owe tax
HM Revenue and Customs (HMRC) will usually collect the tax you owe by changing your tax code. This will increase the tax deducted from your wages, salary or pension, usually in equal instalments for 12 months from the start of the following tax year.
This happens 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.
If you want to, you can pay what you owe before the start of the following tax year.
If you think your tax calculation is wrong
If you think the amounts used in your calculation are wrong, contact HMRC.
You’ll 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’ll be sent a new calculation.
If they disagree, HMRC will contact you to explain why.