You can apply for Marriage Allowance online.
If your application is successful, changes to your Personal Allowances will be backdated to the start of the tax year (6 April).
How your Personal Allowances change
HM Revenue and Customs (HMRC) will give your partner their extra allowance either:
- by changing their tax code, usually to 1166M - this can take up to 2 months
- when they send their Self Assessment tax return, if they’re self-employed
Your tax code will also change if you’re employed or get a pension. Your new code will reflect your new Personal Allowance and will end with ‘N’.