Thousands of people are being warned they could be missing out on up to £252 each year.
HM Revenue and Customs (HMRC) said more than 2.1m couples currently benefit from Marriage Allowance, but estimates that thousands more eligible couples are not claiming the extra cash.
This is often because they don’t realise they may be eligible, particularly couples where one partner has retired, has given up work to take on caring responsibilities, or is unable to work due to a long-term health condition.
READ MORE: Martin Lewis warns of 'frightening' bill changes in letter
Marriage Allowance works by allowing customers who earn less than £12,570 a year to transfer up to £1,260 of their Personal Allowance to their higher-earning partner, to reduce the amount of tax they pay. They can backdate their claim to include any tax year up to 6 April 2018, which could be worth up a total of £1,242 in tax relief.
Couples can use the free Marriage Allowance calculator on Gov.uk to check if they are eligible for the tax relief.
Angela MacDonald, HMRC’s Deputy Chief Executive and Second Permanent Secretary, told the ECHO: “We want every eligible couple to benefit from marriage allowance tax relief. Couples whose circumstances have changed, perhaps one of them has stopped working or taken a lower paid job, may not realise they are entitled to claim."
Those who are eligible can apply at Gov.uk for free and keep 100% of their claim. Successful claims will result in a reduction in the amount of tax paid by the higher-earning partner.
Receive newsletters with the latest news, sport and what's on updates from the Liverpool ECHO by signing up here
READ NEXT:
Spain, Turkey and France update travel advice for UK visitors
Norovirus symptom that affects arms and legs as cases soar
Virgin Money, TSB and Nationwide bank account warning
Iceland's new low calorie meal that 'tastes just like a takeaway'
Bradley Walsh's home life with dancer wife, famous son and link to Coleen Nolan