Are you married or in a civil partnership? Does one of you pay no or little tax, whilst the other pays tax at the basic rate? If so, you may be able to claim marriage allowance all the way back to 5 April 2018.
HMRC explain it here
It’s under claimed and little known, but if you are able to make a back claim it’s a handy cash sum. The total for the four years to 5 April 2022 is £990. Don’t confuse it with married couples’ allowance which is where one person was born before 6 April 1935.
