Seafarer Earning Deduction: Tax guide

RIFT Roundup: The Essentials

• 100% tax relief on qualifying sea earnings: If you are an employee working at sea outside the UK, the Seafarers’ Earnings Deduction (SED) can reduce the UK Income Tax on your qualifying seafaring earnings to zero.

• Strict vessel and location requirements: Relief applies only to work on qualifying ships (excluding offshore oil/gas installations such as rigs, drillships, and flotels) and requires trips that begin or end at a foreign port.

• Rigorous 365-day tracking: To qualify, you must build up an eligible period of at least 365 days outside the UK, tracking midnight locations to ensure no UK stay exceeds 183 consecutive days and total UK time stays under 50% of the period.

If you’re an employee working at sea outside the UK, Seafarers’ Earnings Deduction could significantly reduce the UK Income Tax due on qualifying employment earnings.

SED can provide a 100% deduction for qualifying earnings. That doesn’t mean every seafarer automatically receives all the tax they have paid back. Your employment, vessel, duties, residence status and time outside the UK all have to meet HMRC’s conditions.

Here’s what seafarers need to know in 2026.

Who can qualify for Seafarers’ Earnings Deduction?

HMRC says the deduction is available to employees who meet the relevant residence and seafaring conditions.

You may qualify if you:

• perform all your duties on a ship, or

• perform most of your duties on a ship and your other duties are incidental to that work

• perform qualifying duties outside the UK

• build up a qualifying eligible period, usually at least 365 days

• meet the relevant UK or EU/EEA residence conditions

Crown employees, such as Royal Navy personnel, cannot normally use SED.

Royal Fleet Auxiliary employees are a specific exception. Although RFA employment is treated as Crown employment for tax purposes, RFA employees can qualify for SED if all the other conditions are met.

What counts as a ship?

This is one of the most important parts of the rules.

Tax legislation does not give a simple all-purpose definition of a ship for SED. It does, however, specifically exclude offshore installations used in the offshore oil and gas industry.

HMRC gives examples including:

• fixed production platforms

• floating production platforms

• floating storage units

• floating production storage and offloading vessels

• mobile offshore drilling units, including drillships, semi-submersibles and jack-ups

• flotels

Where a vessel or structure is classed as an offshore installation, earnings from duties performed on it do not qualify for SED, even during periods when the installation is moving, temporarily out of use or being used differently.

The exact status of some vessels can be technical, so vessel type should be checked rather than assumed.

Does working in the North Sea count as working outside the UK?

The answer needs a little care because SED contains two related tests.

For deciding where employment duties are performed, the UK includes its territorial sea. Certain designated parts of the UK continental shelf are also treated as part of the UK where the duties relate to oil and gas exploration or exploitation.

For seafarer duties, HMRC generally treats work on a ship as being performed outside the UK where the ship is on a voyage or part-voyage that begins or ends outside the UK. Voyages that do not involve an overseas port do not satisfy this rule.

The UK sector of the North Sea is treated as part of the UK for this duty-location test.

The calculation of your days of absence is slightly different. If you are physically outside the UK at midnight, a day can potentially count as a day of absence when working out your eligible period, including in some designated continental shelf areas.

For that reason, a simple rule such as “the North Sea counts as the UK” can give the wrong answer when applied to the whole SED calculation.

What is an eligible period?

An eligible period must last for at least 365 days.

The simplest example is a continuous period of at least 365 days outside the UK.

Many seafarers work rotations, so HMRC also allows periods outside and inside the UK to be combined.

For a combined period to qualify:

• no intervening UK period can be more than 183 consecutive days

• at least half of the total days in the combined period must be days of absence from the UK

• the overall eligible period must reach at least 365 days

A day normally counts as a day of absence if you are outside the UK at midnight.

Non-working days outside the UK can count too.

HMRC’s HS205 working sheet is designed to help seafarers test these dates.

How much tax can Seafarers’ Earnings Deduction save?

Where you qualify, SED can provide a deduction of 100% of the qualifying employment earnings attributable to the eligible period, after relevant adjustments.

That can reduce the UK Income Tax on those earnings to nil.

If PAYE tax has already been deducted, this can result in a tax repayment.

Other income can still be taxable, and SED is an Income Tax relief. It should not be read as a blanket exemption from every UK tax or National Insurance charge.

If you have more than one employment during an eligible period, the calculation can also become more complicated.

How do you apply for SED?

If you’re resident in the UK, you normally need to register for Self Assessment and complete a tax return for the relevant tax year.

HMRC’s HS205 helpsheet and working sheet can be used to calculate the eligible period and the amount of the deduction.

HMRC also asks seafarers to retain documents supporting the figures used.

Useful records can include:

• your seafarer’s discharge book

• travel records

• voyage and vessel details

• passport information and visas

• tickets and travel vouchers

• relevant hotel records

• other documents showing when you entered and left the UK

You do not normally send all these records with the tax return, but HMRC can ask to see evidence later.

Different forms apply in some non-UK resident cases. For example, qualifying EU or EEA resident merchant seafarers may use form R43M(SED).

How far back can you claim Seafarers’ Earnings Deduction?

SED repayment claims are subject to time limits.

HMRC’s published SED guidance applies a four-year claim window from the end of the relevant tax year.

For example, a claim relating to the 2022/23 tax year would normally need to reach HMRC by 5 April 2027.

The route used to correct or amend a Self Assessment return can depend on how much time has passed, so older years should be checked carefully rather than assuming they remain open.

Can you get an NT tax code?

Some qualifying seafarers can ask HMRC to issue an NT tax code, which means their employer does not deduct Income Tax from their wages through PAYE.

There are additional conditions.

Among other things, HMRC says you must normally:

• be UK resident

• be in PAYE employment

• work on a vessel accepted as a ship for SED purposes

• submit a Self Assessment return each year

• meet HMRC’s employment-duration requirements

HMRC will not normally issue an NT code until it has processed your first SED claim.

If your circumstances change and you stop meeting the conditions, HMRC needs to be told. Tax can become payable if an NT code was used when the underlying SED conditions were not ultimately met.

Common SED mistakes to avoid

Assuming all offshore work qualifies

Work at sea alone isn’t enough. Offshore installations are specifically excluded.

Counting rotations without checking midnight locations

The absence test looks at where you are at midnight, which can produce a different answer from counting working shifts.

Treating every North Sea day the same way

The location-of-duties rules and the days-of-absence rules are different.

Losing voyage records

SED calculations can cover long periods, so accurate dates and supporting records matter.

Leaving older tax years too late

The claim time limit can close while you’re still working through a later qualifying period.

Need help with Seafarers’ Earnings Deduction?

SED is one of the more detailed employment tax reliefs because several tests have to work together.

RIFT’s offshore tax team can help review your vessel, employment, voyage history and qualifying dates and explain whether an SED repayment may be available.

You can also use HMRC’s current HS205 guidance and contact HMRC directly for free guidance.