Adjusting estimated payrolled benefits after the tax year ends

Payrolling benefits in kind is supposed to make life easier. Tax gets collected through the payroll as you go, rather than clawed back later through a tax code change. That only works, though, if you actually know what the benefit is worth at the point you run payroll. For a fair number of benefits, you don’t. HMRC has built a specific process for exactly this situation.

Early guidance suggested a “month 13” submission would be needed to fix estimated benefits. That instruction has since been dropped in favour of the process below.

Why employers end up estimating

Most payrolled benefits, company cars, medical insurance, and gym memberships have a value you can work out well in advance and spread evenly across the year. The trouble comes with benefits where the final cost isn’t confirmed until after 5 April:

• Benefits invoiced by third-party suppliers, where the final bill lands weeks or months after the tax year has closed
• Usage-based costs, such as some fuel or expense reimbursement arrangements, that aren’t settled until year-end reconciliation
• Complex benefit or reward schemes still being finalised with external providers

Rather than hold up payroll waiting for exact figures, HMRC lets employers payroll a reasonable estimate during the year, then correct it once the real numbers come in.

The correction window

Once the tax year ends, there’s a defined window to swap estimated figures for actual ones.

• All benefit values must be finalised and reported by 6 July following the end of the tax year, the same deadline that currently applies to P11D submissions.
• Any additional Class 1A National Insurance from the correction must be paid by 22 July.

That mirrors the existing P11D timetable on purpose. The reporting method is changing; the deadline structure isn’t.

How the adjustment works

1. Recalculate the true value. Once actual costs or usage figures are in, work out what the annual taxable value should have been.
2. Compare it to what was already payrolled. The gap between the in-year estimate and the final figure is the adjustment, and it can run either way, an underpayment or an overpayment of tax and Class 1A NIC.
3. Report the correction. If the employee is still on the payroll, the correction goes through as a further FPS carrying the true-up figures. If they’ve left, or a director takes no salary, you still need to report the benefit and pay the Class 1A NIC due, through a submission showing no earnings alongside the benefit adjustment.
4. Leave the tax difference to HMRC’s own processes. Any Income Tax that couldn’t be collected through payroll in-year isn’t chased through a one-off deduction. It’s picked up in the employee’s normal end-of-year reconciliation, a P800, a simple assessment, or their self-assessment return. HMRC has also said it will consider spreading larger underpayments across more than one tax year rather than collecting the whole amount at once.
5. Settle the Class 1A NIC. Any extra employer Class 1A NIC from the correction is a straightforward employer liability, due by 22 July.

Overpayments work the same way, just in reverse

If the estimate turns out too high, the same channels apply in the other direction. The employee’s P800, simple assessment, or self-assessment position adjusts down, and any Class 1A NIC that was over-declared gets corrected in the employer’s own reporting.

Why this matters more from 2027

Payrolling has mostly been voluntary up to now, so estimate-and-correct has only really applied to employers who’d opted in. That changes with mandatory payrolling, phased in as follows:

• From 6 April 2027: company cars, car fuel, vans, van fuel, and employer-provided medical benefits
• From 6 April 2028: the remaining benefits, including loans and living accommodation

Once those phases land, far more employers will be payrolling far more benefit types, so “we don’t know the final figure yet” is going to come up a lot more often, particularly for anything tied to a third-party supplier whose invoicing doesn’t line up neatly with the tax year. A reliable process for flagging,
estimating, and correcting these benefits stops being a nice-to-have and becomes a routine part of the payroll year end.

Practical checklist for payroll teams

• Flag estimated benefits at source. Keep a running log through the year of which benefits were reported on an estimate rather than a confirmed figure, and why.
• Chase final costs early. Push third-party suppliers for final invoices as soon as possible after 5 April. 6 July arrives faster than it looks.
• Build the true-up into your year-end timetable, not as something you remember once the P60s are out the door.
• Communicate with affected employees. A shifted benefit value can mean a change in take-home pay, a P800 bill, or a tax code change. A short explanation heads off a wave of confused queries.
• Model the Class 1A cash flow impact. A cluster of underestimated benefits can create a meaningful, lumpy liability due by 22 July, worth flagging to finance rather than discovering on the payment date.
• Keep the audit trail. Record the original estimate, the final value, the reason for the difference, and the date the correction was reported. That’s what evidences compliance if HMRC ever queries the figures.

Estimating a benefit’s value mid-year isn’t a compliance failure. HMRC built the payrolling system to accommodate it. What matters is the discipline in the correction – identify what was estimated, recalculate it promptly once real figures land, report the adjustment through payroll (or an FPS showing no pay, where
relevant) by 6 July, and settle any additional Class 1A NIC by 22 July.

As mandatory payrolling rolls out from 2027, this year-end tidy-up moves from a niche voluntary-scheme issue to a standard part of the payroll calendar, worth building into your procedures now rather than later.