Seafarers' Earnings Deduction Explained | SED Rules & HS205 Guide

Who qualifies for the Seafarers' Earnings Deduction

SED is available if you meet all three conditions:

You work on a ship. Your duties must be performed on a vessel that qualifies as a ship. Offshore installations - fixed platforms, FPSOs, drilling units, flotels - do not count, even if they float.
You have a foreign port voyage. At least one voyage (or part of a voyage) in each employment must begin or end at a port outside the UK. A voyage solely between UK ports does not meet this requirement. Non-UK offshore installations outside UK waters can count as a foreign port for this test.
You're a UK or EEA resident. You must be resident in the UK or in another European Economic Area state for tax purposes.

Who does not qualify

Crown employees - including Royal Navy personnel. Royal Fleet Auxiliary employees are an exception; they're civilian employees and can claim if they meet the other conditions.
Non-UK/EEA residents - you must be resident in the UK or an EEA state for tax purposes.
Offshore installation workers - work on fixed platforms, FPSOs, drilling units, or other structures not regarded as ships does not qualify. North Sea installations within UK waters are treated as being in the UK.
Non-seafaring duties - any work ashore must be incidental to your duties on board. If the work itself isn't seafaring, SED doesn't apply.

If you have more than one seafaring employment in a tax year, each must independently meet the foreign port requirement. The qualifying day calculations apply across employments, but the foreign port test is per employment.

The three key rules

Three rules determine whether your time outside the UK adds up to a valid eligible period. Break any one of them and your period ends.

1. The 365-day rule

Your eligible period must last at least 365 days. It's built from days when you were outside the UK at midnight. The day you leave counts as abroad. The day you return does not - you'll be back in the UK at midnight that night.

Travel days, rest days, and holidays all count as long as you were outside the UK at midnight. The 365 days don't need to be consecutive - you can return to the UK during the period, subject to the next two rules.

2. The half-day rule

After every return to the UK, HMRC checks the running total. Your cumulative UK days must not exceed half the total days in your eligible period so far. If they do, your period ends on the previous return date and you have to start a new one from your next departure.

This is the rule that catches people. A few extra weeks ashore in the early stages of a period, when the total day count is still low, can push UK days over the halfway mark. Later in a well-established period, you have more margin.

3. The 183-day UK visit limit

No single UK visit can last more than 183 consecutive days. If it does, your eligible period ends on the previous return date. This is separate from the half-day rule - you need to satisfy both.

In practice, most seafarers won't hit 183 consecutive days ashore. But it's worth knowing the limit exists, particularly if you're between contracts or on extended leave.

Building your eligible period

Your eligible period starts the day you leave the UK and are outside the UK at midnight. From there, you keep adding trips abroad and return visits. After every return, the half-day rule and 183-day limit are checked.

How days are counted

A day counts as "abroad" if you are outside the UK at midnight. HMRC generally expects you to be beyond the UK's 12-nautical-mile territorial limit. If your ship sails from one UK port to another, it needs to be outside the 12-mile limit at midnight for that day to count.

The Channel Islands, Isle of Man, and Republic of Ireland all count as outside the UK for SED purposes.

Holidays and non-working days

Holidays abroad count. Any day you're outside the UK at midnight is a qualifying day, whether you were working, on shore leave, or on holiday. There's no limit on how many holiday days you can include. Keep evidence of your travel - boarding passes, bank statements, receipts.

What happens when a rule is breached

If the half-day rule is breached on a return, your eligible period doesn't end on that return date. It ends on the previous return date. The same applies for the 183-day limit. You then start a new eligible period from your next departure.

This means a breach doesn't just cost you the current visit - it can wipe out the last trip abroad too. Understanding exactly how close you are to a breach before you come ashore is the difference between keeping your period and losing months of qualifying time.

Combined periods

An eligible period can be a single stretch of consecutive days abroad, or a "combined period" made up of three parts: period A (abroad), period B (in the UK, up to 183 days), and period C (abroad again). The half-day rule applies across the whole combined period. Period B is the UK gap between two stretches abroad.

The HS205 working sheet

The HS205 is HMRC's official form for calculating your eligible period. It's a table where you enter each departure and return, and the columns track your running totals. You can download it from GOV.UK.

Key columns

Column D - Days in UK. The number of days in each UK visit. If any single value exceeds 183, your eligible period breaks.
Column E - Total days. Running total of all days (abroad + UK) since the period began. When this reaches 365, you've met the minimum length requirement.
Column H - Half-day rule breach. If this column shows YES, your UK days have exceeded half the total. Your eligible period ended on the previous return date.

SeaClaim implements the full HS205 methodology and generates a completed working sheet as a PDF - columns A through H - ready for your Self Assessment or your accountant.

Records HMRC expects

HMRC can check your claim at any time. Keep the following:

Completed HS205 working sheet
Passports and visas
Air tickets and travel documents
Seafarer's discharge book
Freeboard logs of the ships you served on
Hotel bills, accommodation receipts
Employment contracts and payslips

HMRC may also contact your employer to confirm voyage and crew details. The more evidence you have, the stronger your position if they enquire.

How to claim

UK residents

Register for Self Assessment and file a tax return for the relevant tax year. Include your completed HS205 working sheet. The SED deduction goes in box 11 of the additional information pages (SA101). Only earnings from qualifying seafaring employment during your eligible period are deductible.

EEA residents (not UK)

If you're resident in an EEA state but not the UK, you claim using form R43M(SED) rather than Self Assessment.

Time limits

You have four years from the end of the tax year to make a claim. After that, the window closes.

NT tax code

After your first successful SED claim, you can ask HMRC for an NT tax code. This tells your employer to pay you without deducting PAYE tax. To qualify, you need to be a UK resident in PAYE employment with a contract of at least 12 months (or 6 months of continuous employment with the same employer). You'll still need to file a Self Assessment return each year.

National Insurance

SED applies to income tax only. National Insurance contributions are still due even if your income tax is reduced to zero through SED.

How SeaClaim helps

SeaClaim tracks the rules described in this guide automatically. Log your voyages and it applies the full HS205 methodology - the 365-day rule, half-day rule, 183-day limit, and foreign port requirement.

Plain-English explanations for every eligibility result, including which rule was breached and how far short you were
Live dashboard showing days in hand, predicted fail date, and 183-day UK tracking
HS205 working sheet PDF export ready for Self Assessment or your accountant
Free to start. See pricing and download.

Sources

This guide is based on the following HMRC guidance and legislation: