US & UK tax deadlines for expats: A practical guide from a US tax specialist on how to get your ducks in a row

If you are a US citizen living in the UK, you already know the tax situation is not straightforward. You are filing in two countries, under two different systems, with two tax years that do not align.

From our perspective as US tax specialists working with expats, the issue is not just compliance, it is timing. Understanding how the US and UK tax calendars interact helps you avoid penalties, reduce stress, and manage cashflow more effectively.

Let us walk through it clearly.

Why the US and UK Tax Calendars Clash

The root of the complexity is simple

The US tax year runs from 1 January to 31 December
The UK tax year runs from 6 April to 5 April, administered by HM Revenue and Customs (HMRC)

That misalignment creates a lag. By the time you need to deal with your US taxes, your UK tax year has only just ended, and in many cases your final UK tax figures are not ready yet.

Key Dates You Need to Know

The US and UK Tax Calendar can be a complicated and overlapping process, but we have got this down to a fine art. Here is the year in brief and month by month detail on what you need to be aware of to hit those deadlines and avoid late penalty fines.

The Year In Brief:

31^st January: Make first UK payment on account (added this as you referenced a second payment in July, so need to reference the fist)

6^th April: Provide documents such as P60

15^th April: estimate and pay any US tax due

15^th June – text is fine

31^st July: Deadline to make second UK payment on account

15^th October – text fine

31^st January: Deadline to pay HMRC (UK Taxes) (keep this as shows a cycle)

January The UK’s Biggest Deadline

31 January UK self-assessment tax return final filing deadline date
UK self assessment tax return due
Balancing payment for the previous tax year
First payment on account for the current tax year

For most expats, this is the largest single tax payment of the year. It often catches people off guard, especially in their first year in the UK.

April The US Payment Deadline & Filing Open for UK Taxes

6 April : Filing is open for UK taxes from the previous tax year

15 April: Tax payment due to the Internal Revenue Service. Standard US filing deadline.FBAR filing date which is automatically extended

Here is the catch. Your UK tax year has just ended on 5 April, but you may not yet have finalised your UK tax liability.

What this means in practice is you may need to estimate your UK tax position in order to calculate your US Foreign Tax Credit.

Even if you do not file yet, any US tax owed must still be paid by this date to avoid interest.

June The Expat Advantage

15 June: Automatic filing extension for US expats

If you live outside the US, you get an extra two months to file your US return. No paperwork is required.

This is often the first realistic opportunity to file once your UK numbers are clearer.

July Another UK Payment

31 July: Second payment on account due to HM Revenue and Customs

This is the follow up to your January payment and can feel like a second financial hit if you have not planned ahead.

October The Real US Filing Deadline

15 October: Extended US filing deadline if you submit an extension. Final FBAR deadline

For many expats, this is the most practical filing date. By now your UK tax position is usually much clearer, allowing for more accurate reporting and better planning.

December Rare but Useful

15 December: Additional extension available on request from the Internal Revenue Service

This is typically reserved for more complex situations, such as business owners or those with international structures.

The Cashflow Pressure Points

There are three moments in the year where expats tend to feel financial strain

January UK tax bill plus first payment on account
April US tax payment deadline
July Second UK payment on account

Planning for these in advance is essential. Without it, even high earners can feel stretched.

Common Mistakes We See

Even financially savvy expats run into avoidable issues. The most common include

• Assuming UK tax automatically eliminates US tax
• Filing US returns too early using incomplete UK data
• Missing the fact that extensions to file are not extensions to pay
• Overlooking reporting requirements such as FBAR

And perhaps most importantly

Underestimating how different types of income are treated across borders

UK employment income is usually straightforward. But things get more complex with…

• ISAs
• UK investment funds which are often treated unfavourably in the US
• Rental income
• Self employment or company structures
• Pension contributions and growth

Final Thoughts

Managing US and UK taxes is not just about meeting deadlines. It is about understanding how the systems interact.

When you get the timing right, you can

• Minimise double taxation
• Avoid unnecessary penalties
• Smooth your cashflow across the year

And most importantly, you remove a significant amount of stress from your financial life.

If you are navigating both systems, it is worth planning your year in advance rather than reacting to deadlines as they arise.