It’s important you give HMRC all the information they ask for so you don’t end up on the wrong tax code and pay too much or too little tax.
If you think you’ve paid too much tax
It’s worth checking how much tax you’ve paid on your wages.
If you think you’ve overpaid tax, you can check if you’re due a refund on the GOV.UK website or use the HMRC online tax checker.
Depending on your circumstances, you might be able to ask for a refund using a form, or you might need to contact HMRC directly.
If you think you haven’t paid enough tax
If you think you’ve underpaid tax, then you might have to complete a tax return.
If this is the case, normal self-assessment time limits apply.
To pay an amount up to £3,000 through an adjustment to your tax code for the following year, you should file a return by 31 December following the end of tax year.
Otherwise, tax still due for the last tax year must be paid by 31 January following the end of the tax year in which the income arose.
If you think you haven’t paid enough tax, contact HMRC.
You might be asked to complete a tax return. Be aware if you don’t do this, you will normally have to pay penalties and interest once the underpayment does come to light.