Merchant Navy Seafarers' Earnings Deduction UK 2026/27: How the 100% Exemption Works

The Seafarers' Earnings Deduction (SED) is a 100% UK income tax exemption on qualifying foreign earnings for eligible seafarers — someone who works on a ship (not an offshore oil/gas installation) and meets a residency and time-outside-the-UK test can have all their qualifying earnings from that employment exempt from UK income tax, though the earnings are still declared on a Self Assessment return.

Broadly, you need to be UK resident, work as a seafarer on a ship during an 'eligible period' of at least 365 days, and spend enough of that period outside the UK (generally, no more than half the days in the eligible period can be spent in the UK). The eligible period can straddle more than one tax year, and the exact day-counting rules are detailed, so it's worth checking your specific voyage pattern against HMRC's guidance or with a specialist adviser.

No — SED is specifically an income tax relief. National Insurance is a separate question, governed by its own rules (including, for some seafarers, EU/international social security coordination agreements depending on the flag state and employer), and needs to be assessed independently of whether SED applies to the income tax side.

Without SED, income tax on £45,000 would be roughly (£37,700 × 20%) + (£45,000 − £50,270... in this case below higher threshold) — approximately £6,486. With SED applying and 100% of the earnings exempt, the income tax liability on this employment falls to £0, a saving of the full £6,486, though National Insurance may still be due separately.

HMRC's definition of a ship for SED purposes excludes offshore installations (oil rigs, some types of offshore wind service vessels used in a fixed installation role) — the relief is aimed at genuine seafaring on vessels that move between ports, not fixed or semi-fixed offshore structures, so workers in offshore energy roles need to check carefully whether their specific vessel and role qualifies.