Before you look at the calendar, list the work in progress. That list is the whole job.

Four things usually sit in it. A VAT return part way through a quarter. Payroll, with a pay date and pension filings attached. Year end accounts and the corporation tax return, which may be partly prepared and partly billed. The director’s self assessment, if your firm handles it.

Once you can see the list, the timing answer writes itself. A gap right after a VAT return has gone in, with payroll just run, is the quietest week of your quarter. That is a clean point to move, whatever month it falls in.

The awkward version is leaving halfway through a set of accounts you have already paid for. You either pay twice or ask the outgoing firm to finish work it has lost interest in. Neither is fatal, and plenty of clients still decide it is worth it, but go in knowing which one you are choosing.

Get the scope in writing before you sign anything. Who finishes the current year, who starts the next, and what each firm is billing for.

Most of the handover sits with the incoming accountant. Your part is short, and it starts with a written notice.

Tell your current firm in writing that you are moving. Check the engagement letter first for the notice period and anything still owed. If fees are outstanding for work done on your records, the old firm can hold those records until they are settled, so clear the account if you want the paperwork to move quickly.

Then your new accountant sends a professional clearance letter. That is a professional ethics step, asking whether there is any reason not to act and requesting the information needed to carry on: opening balances, last filed accounts and tax returns, losses carried forward, capital allowance pools, payroll and pension data.

Authorisation with HMRC runs alongside it. It is not one switch. VAT uses a digital handshake, other taxes use the online agent authorisation route or a paper 64-8. Authorise the new firm before anyone removes the old one, because a fresh authority replaces the one before it, and a gap in access is how filings get delayed.

This is the part competitors gloss over. Nothing about changing firms moves a due date.

HMRC’s position is plain: the tax is yours, the return is yours, and you should check it before an agent files it. If a VAT return is late during the handover, the penalty lands on the company, not on either accountant.

So work backwards from the dates rather than forwards from your notice letter:

• Move between pay cycles, so staff are paid on time and the pension submission is not split across two firms.
• Avoid starting the week a VAT return is due. Start the week after it is filed.
• If a sole trader income stream is inside Making Tax Digital for Income Tax, the quarterly update dates of 7 August, 7 November, 7 February and 7 May sit in the middle of any switch.
• Expect January to be slow going. Every practice in the country is filing self assessments up to 31 January.

Ask your new accountant, in writing, which filing they are taking first and by when. If that answer is vague, you have your signal.

Waiting is the right call in two situations, and only two.

The first is a set of accounts already well under way and already paid for. Let the outgoing firm finish and file, then move with a clean opening balance sheet. The handover is faster and nobody argues about who owns the numbers.

The second is a live transaction. A funding conversation, a sale, a restructure or a lender review. Changing the people who know the history in the middle of that adds risk for no return.

Everything else is a reason to move sooner. Penalties you paid because a deadline slipped. Errors you found yourself. A fee that went up while the service went down. A new account manager every year who asks you the same questions your last one asked.

One fair test before you go: have you actually told your current accountant what you want? Some firms have never been asked for a tax forecast or a VAT scheme review, because compliance work is all anyone requested. Ask once. If the answer is a quote for extra hours, you have learned what their package really covers.

The switch only pays off if the next firm is different in a way you can name. Four questions get you there.

Who does the work, and who replies? Ask whether you are dealing with the person who reviewed your accounts or with whoever is assigned to your file that year. I took a construction client on after a large practice reassigned him repeatedly and he asked to be switched back to me every time. Nexus takes three new clients a month so that stays possible.

Is advice inside the fee? VAT scheme, salary and dividends, and a corporation tax forecast should be part of the monthly work, on a fair-use basis, rather than an hourly extra you have to request.

Will anyone review the set-up? Every client who joins Nexus gets their structure, VAT scheme, pay and software reviewed, with a written note of what should change and why. One procurement consultant moved from standard VAT to the flat rate scheme after that review, and his VAT bill fell every quarter with no change to turnover.

When will I know my tax bill? A month before it lands is the answer you want.