Switching US UK Tax Accountants Mid-Year Without Missing a Deadline

Switching US UK tax accountants mid-year is safe if you do three things in order: map every IRS and HMRC date that falls in the next six months, collect your records before you give notice, and move the authorisations so that the new firm, not the old one, hears from each tax authority. The deadlines carry on regardless of who is acting for you.

This guide is for Americans in the UK, British nationals in the US and other dual filers who have decided to change firms, or are close to deciding. It covers what keeps running during a handover, when in the year a move is easiest, which records to take, and how authority to act for you is transferred on each side.

Can you change US UK tax accountants in the middle of the year?

Yes. No rule in either country ties you to a preparer for a tax year, and an engagement letter normally lets either side end the arrangement on notice. A return can be started by one firm and finished by another, and different firms can sign different years.

What a mid-year change does create is a gap. For a few weeks one firm has stopped working and the other has not yet got the file. For a single-country taxpayer that gap usually falls in a quiet month. For a dual filer it rarely does, because the US and UK calendars are offset: the US tax year is the calendar year and the UK tax year runs from 6 April to 5 April, as our article on the UK tax year and the US tax year explains. Between them there is a filing or payment date in most months.

The deadlines that keep running while you switch

Write these into your own diary before you speak to either firm. All dates move to the next business day when they fall on a weekend or holiday.

Date	Country	What is due
15 January	US	Fourth estimated tax payment for the previous calendar year
31 January	UK	Online Self Assessment return, balancing payment and first payment on account
15 April	US	Regular due date for the federal return and tax; first estimated payment; FBAR
15 June	US	Automatic two-month filing date for those living abroad; second estimated payment
31 July	UK	Second payment on account
15 September	US	Third estimated payment
15 October	US	Extended filing date; automatic extended FBAR date
31 October	UK	Paper Self Assessment return

The sources for each line are official. The IRS lists the four estimated tax due dates as 15 April, 15 June, 15 September and 15 January of the following year. It gives citizens and residents living abroad an automatic two-month extension to 15 June, claimed by attaching a statement to the return, but says interest is still charged on any tax not paid by the regular due date. The FBAR is due on 15 April with an automatic extension to 15 October.

On the UK side, GOV.UK gives the 2025 to 2026 Self Assessment deadlines as 31 October 2026 for paper returns and 31 January 2027 for online returns. Payments on account are due by midnight on 31 January and 31 July, each usually half of the previous year's bill, unless that bill was under £1,000 or more than 80% of it was collected outside Self Assessment. Our guide to HMRC payments on account covers how they are calculated.

The point of the table is the payments as much as the returns. A handover that delays a return can often be rescued with an extension. A missed estimated payment or payment on account cannot be extended, and nobody will remind you if the firm that used to calculate them has stopped.

When is the best time to switch?

Just after a filing cycle closes, and never in the month before a deadline. For most dual filers that points to one of two windows.

February to early April. The UK return and January payment are behind you, and the US return for the previous calendar year is not yet due. A new firm has time to read the earlier returns before preparing its first one.

Late October to December. The US return has been filed, on extension if needed, by 15 October. The UK online return is not due until 31 January. A firm taking over now can prepare the UK return with the US figures already final.

If you are reading this in mid-October with a US return still open, do not move that return. Let the current firm file it, or agree in writing that it will, and switch from the next piece of work. Our article on missing the 15 October deadline abroad explains what is at stake.

What records should you take with you?

More than the returns. A cross-border file contains figures that carry from year to year and cannot be rebuilt from the forms alone. Ask for these before you give notice, while goodwill is intact.

• Signed copies of the last three years of returns in both countries, with all schedules and supplementary pages.
• FBAR filings and confirmations for the same years.
• Workings behind the foreign tax credit, including any unused credits carried forward.
• Any treaty positions taken and elections made, with the year each began.
• Schedules for rental property: cost, improvements and depreciation claimed to date on the US side.
• Cost basis and purchase dates for investments, in both currencies, and the exchange rates used.
• Pension statements and a note of how each pension has been treated on the US return.
• UK losses carried forward and the payments on account already made for the current year.
• Open correspondence with the IRS or HMRC.

Your right to the records

On the US side there is a published standard. IRS guidance on Circular 230, the rules for those who practise before the IRS, says a practitioner must, at the client's request, promptly return any records of the client that are necessary for the client to comply with federal tax obligations, and that a dispute over fees generally does not relieve the practitioner of that responsibility. The practitioner may keep copies. The guidance draws a line at work product that has been prepared but not yet delivered, where the contract requires payment first.

In practice that means your own documents and the returns already delivered to you should come back promptly. A return the old firm has half prepared and not been paid for may not.

What you can get without the old firm

You can rebuild a good deal directly. The IRS lets you view, print or download transcripts through an Individual Online Account, or request them by post. HMRC provides an SA302 tax calculation for the last four years and a tax year overview for any year through your online account, or from commercial software if that is how the return was filed.

Transcripts and SA302s show what was filed. They do not show why. The workings and elections in the list above still have to come from the old firm or be reconstructed.

Keep what you collect. The IRS says to keep records for three years in the ordinary case, six years where more than 25% of gross income was left off a return, and indefinitely where no return was filed. GOV.UK says to keep records for at least 22 months after the end of the tax year when the return was sent on time, and longer if you are self-employed. With carried-forward figures in both countries, most dual filers should keep far more than the minimum.

How do you move the authorisations?

By replacing them, not just adding to them. Until the old authority is gone, each tax authority may still deal with your former accountant.

IRS

Representation before the IRS is authorised on Form 2848. The instructions say a newly recorded power of attorney will generally revoke any earlier one recorded for the same matter. If you want an existing representative to stay in place, for example a firm handling an open examination, you tick the box on line 6 and attach copies of the powers you are keeping.

To end an authority without appointing a replacement, the instructions say to write REVOKE across the top of the first page of the existing form, sign and date it below, and send it to the IRS. If you have no copy, a signed statement listing the matters, the periods and the representative's name and address does the same job. A representative can withdraw in a similar way.

HMRC

GOV.UK explains that you can authorise an agent such as an accountant or tax adviser to manage your tax affairs, and that for Self Assessment HMRC then sends correspondence to the person you have authorised, except tax bills and refunds. That is why a stale authorisation matters: an enquiry letter or a notice can go to a firm that no longer acts for you.

Ask the new adviser how they will be authorised and get written confirmation of two things: that their authorisation is active, and that the previous agent has been removed. If you are unsure whether the change has gone through, ask HMRC directly.

A handover plan in eight steps

1. List the next six months of dates from the table above, with the amounts due where you know them.
2. Choose the new firm first. Agree scope and fee in writing before you tell the old one. Our buyer's checklist has the questions to ask.
3. Download what you can yourself: IRS transcripts, SA302s, tax year overviews and FBAR confirmations.
4. Request the file from the old firm in writing, using the list above, and settle any undisputed fees.
5. Decide who finishes work in progress. Anything due within about six weeks is usually best completed by the firm that started it.
6. Give notice in line with the engagement letter and ask for confirmation of the date the firm stops acting.
7. Move the authorisations: a new Form 2848 or Form 8821 for the IRS, a new agent authorisation for HMRC, and removal of the old ones.
8. Have the new firm review the last filed year in both countries before it prepares anything new, and tell you about any position it would have taken differently.

Illustrative example: an American designer in Edinburgh decides in June to leave the firm that has prepared her returns for four years. Her US return is on extension to 15 October and her second UK payment on account is due on 31 July. She appoints a new firm, pays the July instalment herself from the figure on her last statement, and asks the old firm to finish and file the US return since it is half prepared. The new firm takes over from the UK return due in January, receives the foreign tax credit workings in August and finds an unused credit carryover that had not been applied. Because the handover was planned around the two dates, nothing was late. This example is illustrative and does not describe a real client.

What people get wrong when switching

Leaving before the file arrives. Once you have given notice, your request for workings is at the bottom of someone's list.

Assuming the returns are the file. Carryovers, elections and basis records live in workpapers. Without them a new firm starts from zero or guesses.

Forgetting the payments. Estimated tax and payments on account fall between returns and are the first thing to slip.

Leaving the old authorisation in place. HMRC letters keep going to the former agent, and an old Form 2848 for a different matter may still be live.

Switching one country only. Moving the US return to a new firm and leaving the UK return where it was recreates the gap between the two that most people are trying to close. See how the two sides should fit together in our guide to the US/UK cross-border tax preparation process.

Expecting the new firm to adopt every old position. A careful firm will review earlier years and may recommend changes. That is part of what you are paying for.

Making the move

A change of accountant is an administrative project with fixed dates. Set the dates out, secure the records, transfer the authorities, and let each firm finish what it is best placed to finish. Done in that order, a mid-year switch costs you nothing in penalties or interest.

US/UK Cross Border Tax — US CPAs and UK tax advisers working as one team; London, Manchester, New York, San Francisco. Our cross-border tax service takes over both returns on one file, starting with a review of the last year filed. To plan a handover around your own dates, speak to our US UK tax accountants.