Can someone explain how this works please? What information is included and what is taxed? For UK/USA dual citizens that don't work when should it be completed for each tax year?
I am waiting to speak with a tax consultant but was hoping to understand the process a little better. Thanks.

If you don’t work then are you sure you need to complete one? But essentially it will be all income i.e. property income, pensions, interest, etc, and any claimable expenses. It’s much easier than the US ones I think. What you’re actually taxed on will depend on where you’re tax resident and where the source of the income is.

It's not too complicated, and it doesn't cost anything to complete a self-assessment (you don't have to buy Turbo Tax software or equivalent). From memory, you have to set up a Government Gateway account, and (I think) apply for a tax ID number. After that's all set up, you can log in and do dummy runs of your self-assessment - so you can save it and go back and make amendments, etc.

The deadlines to submit are quite late, so you have plenty of time to figure it all out. If you file online, the deadline for the 2024-2025 tax year is 31 January 2026.

The bit that may be complicated is your personal tax situation, but the actual process of completing a tax return is not complicated. As an example, I just did a dummy run of mine yesterday for 2024-2025 and it took me about an hour, even though I have multiple sources of income in the US and UK. I'm a US non-resident, non-citizen but I believe if I were a US citizen the tax situation might be a bit more complicated to understand.

Best thing to do is just Google "How do I submit a tax self-assessment in the UK?" and use the results to set up your account, and then just play with the online process. It takes you through various sections and has information boxes to explain what each section is. I think if you did this you'd learn a lot and will then have more specific questions to ask.

You say you don't work - if you don't have any sources of income, it will be very straightforward as you won't need to complete a UK self-assessment. If you have non-work sources of income, maybe give us an idea of your general income situation if you want specific help understanding how to declare the various sources of income in the US and UK and how to deal with the split tax year (UK tax year is April to April, unlike the US).

I will have income going forward, pensions, investments and bank interest. And I guess first year will be a split year, is that complicated?

From which country? Both or just US/UK? Either way it’s not complex, we have income from both and it’s pretty easy to do yourself, or you can hire somebody to do it for you if you prefer (have a look at it and see what you think).

Like @dunroving I’ve just done mine for the UK and it took me less than an hour too, despite numerous income streams on both side of the Atlantic. It’s a heck of a lot easier than the US tax returns!!

When I referred to "split year", I meant the UK has April to April tax year and US is calendar year tax year (Jan to Dec). This only really matters for people who have to complete both a US and UK tax return. I don't so it's a non-issue for me, but there are several people on this sub-forum who do, so they'll be able to tell you how they deal with it.

Hello kateg60,

Your personal circumstances would need to be looked at in more detail.

You should seek professional advice.

It is a bit more work as in the US employers or companies or financial institutions or the government report on a calendar year basis via forms such as W2, K-1, 1099s- thus there is always an almost 4 months difference between the US on a calendar year basis, and the UK on a fiscal year basis : so one has to be careful to account for the difference.

On the first year back, need to track the dates one is subject to filing a UK return,and how that effects the US return one may need to keep filing even if one not a US citizen.

The UK self-assessment return is quite simple to understand compared to the US tax returns. The concept of the January 'balancing payment' can at times at first be something to get used to. For example for the ending early April 2024, I filed my self assessment in January 2025 paying the tax due - but there was a 'balancing payment abovet the amount of tax due on the self-assessment which came as a surprize.

The other difference I find is calling the HMRC one gets a more knowledge and helpful agent than calling the IRS.

I've actually found the UK self-assessment more confusing than US, but then when I was in the US I didn't have any UK income (whereas now I'm in the UK, and for many years, I've received both UK and US income). My US tax return was also pretty straightforward because I had just one source of income (job), plus then the potentially confusing part - filling in various forms to claim an offset against tax (such as healthcare costs, mortgage payments, etc., if I recall correctly). But after doing it for one year, using TurboTax, the following years were just a case of keeping good records.

Not 100% sure what you mean by the "balancing payment", but the confusing part of UK S-A for me has been the payment "on account" for the following year (I think that's what you are referring to). It assumes your income the following year will be the same as the current year and so it is asking you to pay tax in advance of doing next year's tax return (which is fair enough, as PAYE tax is paid during the year it's earned). If all your income is PAYE, it's pretty straightforward, except in situations where you take irregular payments such as withdrawals from a defined contribution pension (e.g., SIPP). The pension company often uses emergency tax code (assuming that you will take the same amount out every month for the year).

My income has been inconsistent from year to year for about 5 years now, due to US Social Security errors, then WEP, then a new US annuity, then starting to receive UK state pension and then this year deciding to withdraw £14k from my SIPP to use up the headroom in my 20% tax bracket. From next year, everything should be a lot more consistent (I hope!).

Glad that I don't have to fill in both US and UK tax returns, though.

Sorry to the OP if I've taken the thread a bit off-track, but some of the discussion might help you to start looking into some of these things (and especially anticipate the possibility of being asked to make a payment "on account" for the following year.) If that happens and you know for sure that your income for the following year will be less, there are ways to ask HMRC to reduce the amount paid in advance of next year. But don't do it if you aren't sure; it can't be used simply to reduce the tax you pay.

One thing we have done (or rather our tax preparer did) from the first year we were back and having to do HMRC SA returns was to count the US tax year as concurrent with the UK tax year. You make a statement on this in the comments section and say that it is to better align the foreign tax credits. This also means one can use as-is the annual US statements such as W2, 1099R, 1099DIV and SSA statements without trying to calculate the amounts to fit into the UK tax year.

+1

Note that if you reside overseas the IRS deadline has an automatic extension to June 15.

In my case I filed the self assessment in January , for the year ending April 2024, owing X amount- but it HMRC shows a "balancing payment due" of ,25X as well.

Just looking at the US 1040 form I see many more lines of information required compared to my self assessment, and often each line has in the instructions various options.

Are the standard statements or protocols that can be used on the UK assessment that cover the most common tax reportable events? For example, I know I wouldn't pay tax on a Roth withdrawal or conversion or a single IRA distribution in a given year. Is there a standard way to report these vents on the UK self assessment each year?

I have reached out to multiple professionals and they are either not taking new clients or mostly deal with high net worth individuals and so consequently their fees are above my limits. Can anyone personally recommend one of the commonly advertised firms such as Greenback?

For Roth withdrawals or a single IRA distribution then my accountant lists the exact amount in the self assessment comments section and cites the tax treaty as the reason it is not being reported on the return as taxable income.

I have no actual experience of companies such as taxes for expats or Greenback but have them as standbys if or when my accountant retires. She is not taking on new clients and was very late getting our HMRC self assessment done last year.

I have seen elsewhere that though there is an extension to June 15, you still have to pay any tax due by April 15.
Otherwise, you will incur a penalty and interest payments.
Have you come across this anomaly before?