Marriage allowance calculator — both sides of the transfer, priced

One spouse transfers £1,260 of personal allowance; the other gets a £252 tax credit. Simple — except the transfer can cost the lower earner tax if their income is close to the allowance, and the claim closes entirely if the recipient pays higher-rate tax. This calculator prices both sides, with the same function the Hundred Summers app uses. Your figures never leave your browser.

The claim, and the traps around it

Claim free at gov.uk — never through the fee-charging intermediaries that advertise against this exact search and keep up to half the backdated refund. The claim renews automatically every year until cancelled, which cuts both ways: set-and-forget when circumstances are stable, a quiet leak if the lower earner's income rises past the allowance and nobody cancels.

Career breaks, part-time years and early retirement are the classic openings — a retired couple where one partner's pension sits under £12,570 usually qualifies. The full Hundred Summers couples plan checks this automatically from both partners' projections, year by year, alongside the bigger cross-partner moves: pension contributions routed to the higher earner's relief, and retirement drawdown split to fill both personal allowances — see the guides for how those work.