What is the qualifying period for SED?

You must establish a qualifying period of at least 365 continuous days. The period begins on the day you leave the UK to start duties and continues through return visits until a failure of the rules terminates the claim period.

How does the Half-Day Rule work?

Under the Half-Day Rule, when taking your cumulative period as a whole, the total number of days spent in the UK must never exceed half (50%) of the total days elapsed since the beginning of the qualifying period.

What is the 183-day return limit?

No single return visit or stay in the UK can exceed 183 consecutive days. If you remain in the UK for 184 days without departing, your qualifying period is legally broken and your SED claim terminates on the date of return.

Does SED exempt me from National Insurance contributions?

No. The Seafarers' Earnings Deduction only applies to UK Income Tax. Class 1 National Insurance contributions remain payable on your employment earnings unless an employer is based outside the EEA/UK and no reciprocal social security agreement applies.

Do offshore oil rigs and drilling barges qualify as ships?

No. HMRC and UK tax tribunal decisions strictly exclude fixed production platforms, jack-up rigs, and floating accommodation units (flotels) from the definition of a 'ship' for SED purposes. The vessel must possess navigation capabilities used in maritime transit.

What is the qualifying period for SED?

You must establish a qualifying period of at least 365 continuous days. The period begins on the day you leave the UK to start duties and continues through return visits until a failure of the rules terminates the claim period.

How does the Half-Day Rule work?

Under the Half-Day Rule, when taking your cumulative period as a whole, the total number of days spent in the UK must never exceed half (50%) of the total days elapsed since the beginning of the qualifying period.

What is the 183-day return limit?

No single return visit or stay in the UK can exceed 183 consecutive days. If you remain in the UK for 184 days without departing, your qualifying period is legally broken and your SED claim terminates on the date of return.

Does SED exempt me from National Insurance contributions?

No. The Seafarers' Earnings Deduction only applies to UK Income Tax. Class 1 National Insurance contributions remain payable on your employment earnings unless an employer is based outside the EEA/UK and no reciprocal social security agreement applies.

Do offshore oil rigs and drilling barges qualify as ships?

No. HMRC and UK tax tribunal decisions strictly exclude fixed production platforms, jack-up rigs, and floating accommodation units (flotels) from the definition of a 'ship' for SED purposes. The vessel must possess navigation capabilities used in maritime transit.

Maritime UK Tax Relief Engine • 2026/27

Seafarers' Earnings Deduction Calculator (2026/27)

Model 100% UK Income Tax exemption under Section 378 ITEPA 2003. Test your qualifying period against HMRC's 365-day rule, the Half-Day rule, and calculate your net take-home pay.

Seafarers' Earnings Deduction (SED) Calculator 2026/27

Model Section 378 ITEPA 2003 100% Income Tax exemption and the Half-Day rule.

Eligible for 100% Seafarers Earnings Deduction (SED)

• 365-Day Qualifying Period: Met• Half-Day Rule (≤50% in UK): Met• Max UK Stay (≤183 days): Met• Qualifying Ship Status: Met

Seafarer Gross Annual Earnings (£/yr)Earnings from duties performed wholly or partly on board a qualifying ship.

Total Days in Qualifying Period: 365 daysMust span at least 365 cumulative days.

Total Days Spent in the UK: 120 daysMax permitted under Half-Day rule: 182 days (245 days outside UK).

Longest Single UK Visit: 45 daysNo single return visit to the UK can exceed 183 consecutive days.

Employment performed on a qualifying ship (cruises, tankers, cargo vessels, tugs)Note: Fixed production oil rigs, jack-up drilling units, and floating accommodation barges are excluded by HMRC statute.

100% Income Tax Saved

£9,432.00

100% Tax Exemption Applied

Class 1 NI Payable

£3,110.60

National Insurance remains due under PAYE

Net Take-Home Pay

£51,889.40

£4,324.00 / month net

Seafarers' Statutory Deduction Notes (2026/27):

• Under Section 378 ITEPA 2003, qualifying seafarers receive a 100% deduction on employment income.

• SED must be reported on the SA100 Self Assessment tax return under the Employment / Seafarers supplementary page (SA102).

• Keep maritime discharge books, passports, flight tickets, and vessel log books for at least 5 years as HMRC proof.

How Section 378 ITEPA 2003 Seafarers Relief Operates

The Seafarers' Earnings Deduction is an exceptionally valuable statutory relief designed to support British and international mariners. When all statutory criteria are satisfied, 100% of employment earnings derived from shipboard duties are subtracted from your taxable income, effectively reducing your UK Income Tax liability to £0.

To claim, you must complete the employment pages (SA102) of your Self Assessment tax return (SA100) and enter the 100% deduction in Box 11, along with providing dates of qualifying periods and vessel names.

Frequently Asked Questions

Clear answers based on official HMRC rules and statutory guidance.

Under Section 378 of the Income Tax (Earnings and Pensions) Act 2003 (ITEPA 2003), eligible mariners working aboard qualifying ships who satisfy strict absence requirements can claim a 100% deduction against UK Income Tax on their seafaring employment earnings.

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Qualifying duties and days matter

Seafarers Earnings Deduction has specific employment, vessel and qualifying-period rules. A qualifying-day count alone does not establish the relief.

Check the foreign-port, UK-absence and relevant employment conditions with HMRC. Offshore installations and some duties do not qualify simply because the work takes place at sea.

Check the rules for your circumstances

Seafarers Earnings Deduction

Official guidance supports the rules described here; it does not approve or certify this calculator. Confirm dates, eligibility and unsupported cases before making a financial decision.