How to Switch Payroll Software Mid Tax Year UK: A Step-by-Step Guide

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Switching Mid Year Is Normal

Changing payroll software feels riskier than it is. Get it wrong and you can end up with duplicate employee records at HMRC, year-to-date figures that do not reconcile, and employees on the wrong tax. Those are real problems, and HMRC keeps flagging them, most recently in its April 2026 Employer Bulletin.

They are also avoidable. You do not have to wait until 6 April, and thousands of UK employers switch mid year without incident. What you need is the right sequence, a complete set of year-to-date data, and a firm grip on how HMRC identifies your employees in RTI.

HMRC does not care which software you use. It cares that submissions are accurate, continuous, and tied to the correct employer PAYE reference and payroll IDs.

Choosing the Moment

HMRC works in tax months running from the 6th of one month to the 5th of the next. The safest switch point is immediately after you have processed and submitted the final payroll of a tax month, and before you start the next one.

Avoid switching mid-period. If pay dates straddle a tax month boundary, which is common on weekly payrolls, make sure every FPS from the old system has been accepted before you move.

One timing risk worth naming: your FPS must still reach HMRC on or before payday during the transition. A switch that overruns is a late submission like any other, with a £100 penalty for employers with one to nine employees, although the first failure in a tax year carries no penalty and neither does an FPS where all payments fall within three days of payday.

Step 1: Finish the Final Period on the Old System

Run payroll as normal, submit the FPS, confirm it has been accepted rather than just sent, pay your employees, and pay HMRC.

Only then is the old system finished. Do not cancel anything yet.

Step 2: Export Everything Before the Subscription Lapses

This is the step that bites people months later. Once a subscription ends, access usually goes with it, and you are required to keep PAYE records for three years after the end of the tax year they relate to.

For each employee, capture:

• Gross pay to date since 6 April
• Tax paid to date
• Employee and employer National Insurance to date
• Employee and employer pension contributions to date
• Statutory payments to date, covering SSP, maternity, paternity, adoption, shared parental, parental bereavement and neonatal care pay, plus any amounts already recovered
• Student loan and postgraduate loan deductions to date
• Payrolled benefits in kind to date, if you payroll them
• Tax code and National Insurance category letter, matching what HMRC holds
• National Insurance number, date of birth, the original employment start date, and the payroll ID

At employer level, note the Employment Allowance claimed to date, any CIS deductions suffered if you are a limited company subcontractor, and your pension scheme details.

Most software produces a year-to-date report or P11 deductions working sheet covering the employee items. Export it for everyone, and keep a copy outside the old system.

Step 3: Set Up the New Software

Employer PAYE reference. Three digits, a slash, then your reference, for example 123/AB12345. It must match your HMRC online account exactly, because every submission is matched on it. Your Accounts Office reference is a different, longer number used for payments, and the two get confused.

Employment Allowance. The claim is made through the EPS, so check how the new software handles it rather than assuming it carries across.

Pension scheme. Re-enter the provider, scheme reference and contribution rates, and carry over the assessment history as well as the contributions: enrolment dates, postponement dates, opt-out dates and your next re-enrolment date. Without that history the new software assesses everyone from scratch, and your auto enrolment records have to survive six years regardless of which system holds them.

Step 4: Payroll IDs, Where This Actually Goes Wrong

Every employee has a payroll ID, sometimes called a works number. HMRC uses it with your PAYE reference to identify one employment. Change it silently and HMRC’s systems read it as a second job, which is how one employee ends up with two employment records, split tax codes and duplicated liabilities.

The simplest route is to reuse the same payroll IDs, copied exactly from the old system, including leading zeros. Where your new software lets you override the IDs it generates, do that.

Where it does not, and several packages generate IDs in the background whether you like it or not, you need three RTI fields populated on the first FPS from the new system: the new payroll ID, the old payroll ID, and the payroll ID changed indicator set to yes. Those are RTI data items 38, 39 and 40, and naming them to your new provider usually saves an afternoon. HMRC’s advice where you are unsure whether the previous software used a payroll ID at all is to set the change indicator anyway.

Do not report continuing employees as new starters. This is the other half of the problem and most guides leave it out. Your new software will treat existing staff as new records internally, which is fine, but a start date or starter declaration must not go to HMRC for someone whose employment is continuing. Submit either and HMRC reads it as a new job, creating exactly the duplicate you were trying to avoid. Use the payroll ID change fields instead. A genuine new starter does need a start date, so the distinction matters both ways.

Do not report a leaving date either. Migration should never produce a leaver. If it does, your employee shows as having left an employment they are still in.

Keep names consistent. Michael rather than Mike, matching what HMRC already holds, since name mismatches are another reason records fail to match.

Step 5: Enter the Year-to-Date Figures

New payroll software will have a section for opening balances or year-to-date figures at the point processing starts. Enter everything you exported, and check it twice, ideally with someone else reading the numbers back.

If your new product has no obvious place to enter year-to-date data, ask their support before going further. It is a basic requirement of any UK payroll package, and a product that cannot take it is telling you something.

Accuracy here outlives the current period: your P60s at the end of the tax year are produced from these figures.

Step 6: Run One Period in Parallel

The step people skip. Process the next period in both systems, submitting only from the new one, and compare gross pay, tax, National Insurance and net pay for every employee.

Differences usually trace back to a wrong tax code, the wrong National Insurance category letter, or a mistyped opening balance. All are easy to fix before submission and tedious to fix afterwards.

When the figures agree, submit the FPS from the new software, pay your employees, and only then cancel the old subscription.

Step 7: Check HMRC After the First Submission

Once the first FPS is accepted, open your HMRC business tax account and look at the PAYE section. You are checking that the submission has been processed, that no employee has acquired a second record, and that the amounts are what you expect.

If duplicates have appeared, contact HMRC’s employer helpline promptly, using the contact details on GOV.UK. Reported early, the records can be matched up. Left alone, they turn into a PAYE account that never balances.

What Not to Do

Do not issue P45s to your staff. A change of software is not a change of employer and nobody is leaving.

Do not amend start or leaving dates that have already been reported to HMRC. Correct them in your software only.

Do not cancel the old subscription until the new system has submitted successfully and you have exported everything.

Do not treat HMRC recognition as a quality mark. It means the software can produce a valid FPS, not that it suits your business.

FAQ

Do I need to tell HMRC I am switching?

No. There is no change-of-software notification. Continuity comes from the PAYE reference, the payroll IDs and accurate year-to-date figures, not from any administrative process.

Can I switch at any point in the year?

There are no legal restrictions. The safest point is right after an accepted FPS for a completed tax month, with no outstanding submissions hanging over you.

What happens to auto enrolment when I switch?

Contributions travel with the year-to-date figures, but the assessment history does not unless you move it: enrolment and postponement dates, opt-out notices and your re-enrolment date. Re-enter the scheme details, confirm the link to your provider works, and test a contribution submission during the parallel run.

I have submitted an FPS with the wrong year-to-date figures. What now?

If it is the same tax year, send a corrected FPS with the right year-to-date figures as soon as you can. For a tax year that has already closed, send a further FPS for that year showing corrected year-to-date figures. The Earlier Year Update is no longer used for this, so ignore any guidance that tells you to file one.

Will my employees notice?

They should not, beyond a payslip that looks different. Tax codes, year-to-date figures and net pay all carry over. If someone’s tax changes sharply in the first period on the new system, stop and check the opening balances before paying them.

Switching Payroll Software Mid Tax Year: The Bottom Line

The sequence matters more than the software. Finish and submit the final period on the old system, export complete year-to-date data before the subscription lapses, set up the new system with the same PAYE reference and the same payroll IDs, enter opening balances carefully, run one period in parallel, and check HMRC afterwards.

If you remember one thing, make it the identity fields. Reuse the payroll IDs where you can. Where you cannot, populate the old ID, the new ID and the change indicator, and keep start dates, starter declarations and leaving dates out of it for anyone whose employment is simply continuing. That single discipline prevents the duplicate records HMRC is still writing to employers about.

This article is general information about UK payroll reporting, not advice, and it does not take account of your circumstances. RTI rules, penalties and HMRC guidance change. Speak to a qualified accountant or payroll professional, and check the current position on GOV.UK, before acting on anything here.