Taxpayers can backdate their entitlement to the marriage allowance to include the tax year before 5 April 2015. You can claim the spousal allowance retroactively for up to five years, but you must check the period before applying. If you or your partner died on or after 5 April 2016, your claim for spousal benefits cannot be backdated to the date of your death, including the year in which you were entitled to these benefits. Taxpayers who claim a spouse split refund for the death of a spouse in the first five years of their marriage can backdate their entitlements to a tax year ending on 5 May 2015 or to a tax year ending on 5 March 2016 if they are not entitled to a spouse split allowance as long as the partner dies before or on 5 June 2016.

If you want to deal with the relatively straightforward Marriage Allowance Refund, you need to go to HMRC's Marriage Tax Allowance page or you can consult with Goldman Knightly Solicitor's expert to apply in the same way and confirm that your circumstances have changed.