7 payroll mistakes quietly costing UK businesses money

1. Not claiming the Employment Allowance

The Employment Allowance is the single most expensive tick-box in UK payroll, and it's the mistake we see cost businesses the most money by a distance. Eligible employers can currently claim £10,500 a year off their employer Class 1 National Insurance bill — money that simply isn't taken from the business once the claim is set up correctly. GOV.UK's guidance on claiming the Employment Allowance confirms the £10,500 figure applies for both the 2025/26 and 2026/27 tax years, so it hasn't been eroded by a freeze the way some other reliefs have. What makes it the costliest mistake we find in reviews is how easily it goes missing: switch provider, switch software, or simply leave the box unticked when the scheme was first set up, and the allowance quietly stops applying with no alert from HMRC telling you it's gone.

Because claims can be backdated up to four tax years — confirmed by GOV.UK's guidance on claiming for previous years — a missed claim from three years ago is still fully recoverable today. Each past year needs its own EPS submission, but once the gap is found, recovering it is largely administrative.

2. Wrong NI category letters

National Insurance category letters tell HMRC's systems how much employer National Insurance to charge on each employee, and getting them wrong is a slow, invisible leak rather than one big error. Employees under 21 should typically sit on category M, apprentices under 25 on a recognised apprenticeship scheme on category H, and qualifying veterans in their first year of civilian employment on category V — GOV.UK's guidance on National Insurance category letters confirms all three attract 0% employer NIC up to the Upper Secondary Threshold of £50,270 a year, reverting to the standard 15% rate above that and automatically from the employee's relevant birthday. The trouble is most payroll systems default every new starter to category A, the standard adult rate, and unless someone checks date of birth and apprenticeship status against the category letter on day one, that default simply sticks.

Multiply the missed 0% relief by every eligible employee, every pay period, across a full tax year, and the total adds up fast — particularly for employers who take on a lot of under-21s or apprentices.

3. Stale tax codes

HMRC issues tax code notices — a P6 for a mid-year change or a P9 for the new tax year — electronically through the PAYE system, meant to be pulled into payroll and applied to the very next pay run automatically. When they aren't, whether because the software wasn't checking for them, a notice was filed and never actioned, or a provider switch left a gap in the process, the employee ends up taxed against an out-of-date code. That can mean too much tax deducted, leaving take-home pay short and generating complaints, or too little deducted, building an underpayment HMRC will eventually claw back, often through a coding adjustment the following year. Either way it's the employer who carries the fallout: queries from confused staff, manual corrections, and in persistent cases direct HMRC contact asking why notices issued months earlier were never applied.

4. RTI errors and duplicate employments

Full Payment Submissions tell HMRC what was paid and deducted for every employee on every pay run, and small inconsistencies in the data — a name spelled differently to a previous employer, a National Insurance number missing from a new starter's first FPS, or an employee record recreated from scratch instead of continued — can cause HMRC's systems to open a second, duplicate employment record for the same person. Once that happens, the business tax account shows liabilities that don't match actual payroll: PAYE and NIC effectively doubled for one employee, or specified charges raised because HMRC assumes a return is missing when it isn't. GOV.UK's guidance on correcting an employer PAYE bill is explicit that duplicate employments must be identified and merged or removed by HMRC directly — an employer can't fix them by editing payroll software, and shouldn't just pay the inflated demand, because that leaves the underlying problem in place.

These need correcting at source, not paying off. A payroll review flagging a mismatch between FPS history and the business tax account is usually the first sign a duplicate employment exists.

5. Missing statutory pay reclaims

Statutory maternity, paternity, adoption and shared parental pay is money most employers can get back from HMRC, not a cost they have to absorb outright — yet plenty of businesses fund it in full each pay run and never claim the offset. GOV.UK's guidance on getting financial help with statutory pay confirms the standard reclaim rate is 92% of what's been paid out, and that small employers — broadly, those whose total Class 1 NIC was £45,000 or less in the relevant previous tax year — can claim Small Employers' Relief and recover more than 100%, with the extra covering the employer's administrative cost. An employer who never applies this relief, or claims the standard 92% when they actually qualify for the small employer rate, is simply donating the difference to HMRC every time a member of staff goes on leave.

Because reclaims are usually handled through the EPS alongside routine payroll, missing the relief once often means missing it on every subsequent claim too, until someone checks eligibility against last year's NIC figure.

6. Auto-enrolment drift

Auto-enrolment isn't a project you complete once and file away — it's an every-pay-run duty that keeps running for as long as the business has employees, and "drift" is what happens when that ongoing legal duty stops getting the attention it consistently needs. New starters need assessing against the age and earnings thresholds every time they join, existing staff need reassessing as pay or age changes, and The Pensions Regulator's guidance on re-enrolment confirms employers must also carry out cyclical re-enrolment and a fresh re-declaration of compliance roughly every three years, picking up eligible staff who opted out the first time around. Common drift includes new starters never assessed, contributions calculated on the wrong pay elements — basic pay only, when qualifying earnings should include bonuses and overtime — and missed re-enrolment dates that slip past unnoticed.

None of this shows up as one dramatic failure; it builds quietly, run after run. The Pensions Regulator can and does fine employers for non-compliance discovered years after the drift began, by which point correcting it costs far more than simply running the assessment correctly each pay run would have.

7. Paying what HMRC says instead of what you owe

When the figure on your HMRC business tax account doesn't match what your own payroll records say you owe, the instinct to just pay it and move on is understandable but usually wrong — a mismatch is a signal to investigate, not a bill to settle without question. Specified charges, which are HMRC's own estimate of what's owed when it believes a submission is late or missing, duplicate employments, and payments received but not correctly allocated against the right PAYE reference or period can all inflate the amount shown, sometimes significantly. GOV.UK's guidance on correcting an employer PAYE bill sets out the route for challenging these figures directly with HMRC rather than paying them off, and reconciling your payroll software's liability reports against the business tax account, period by period, is the only reliable way to catch a mismatch before it costs an unnecessary payment.

A free payroll review checks all seven of these against your actual payroll data and shows you what each one is worth — before you change anything.

Worked example: what these mistakes are worth in pounds

Take a small business with nine employees that switched payroll provider three tax years ago. The Employment Allowance claim didn't carry across, and nobody noticed because payslips and HMRC payments carried on looking normal, while the business stayed eligible every year since. At £10,500 a year, that's £10,500 for the current year plus £10,500 for each of the three missed years — up to £42,000 recoverable once caught, since GOV.UK's guidance on claiming for previous years allows backdating up to four tax years, each via its own EPS. Add a second mistake: one employee took maternity leave, paid £8,000 gross Statutory Maternity Pay, reclaimed at the standard 92% rate, worth £7,360 — but the business's employer Class 1 NIC in the relevant previous tax year was under the £45,000 Small Employers' Relief threshold, so it actually qualified for the 109% small employer rate, worth £8,720. That's £1,360 unclaimed on one period of leave, purely because nobody checked which rate applied.

Common mistakes we see beyond the big seven

Alongside the seven headline mistakes above, payroll reviews regularly turn up a second tier of smaller, more tactical errors that don't cost as much individually but still add up over a full tax year, and are worth checking even when the big seven come back completely clean. These tend to be process failures rather than knowledge gaps — a step skipped under time pressure, a setting never revisited after it was first configured, or a change in an employee's circumstances that payroll was never actually told about. None of them are exotic; they're the kind of thing that happens in any business running payroll manually, or with a system nobody has properly audited in a while, and each one is quick to check once you actually know to look for it in the first place.

• New starter checklists incomplete, so emergency tax codes run longer than necessary
• Student loan deduction plans not updated when HMRC issues a start or stop notice
• Leavers processed late, so final pay, holiday pay and P45s go out wrong
• Apprenticeship Levy miscalculated across connected companies sharing one pay bill allowance
• Pension contribution rates left on old defaults after minimum contributions changed
• Benefits in kind reported inconsistently between payroll and the P11D

Two edge cases worth knowing

Two situations catch out even diligent payroll teams, precisely because they don't fit the usual pattern of "set it up once and it's done." The first concerns veterans and the National Insurance category V relief: the qualifying "first year" clock starts from the date the veteran left the armed forces, not the date they start the civilian job, so an employer hiring someone eighteen months after discharge may find no relief available, while one hiring someone straight after discharge could keep applying category V beyond the point it stops qualifying. The second concerns the Small Employers' Relief threshold: eligibility is based on Class 1 NIC in the relevant previous tax year, not the current one, so a business that has grown past £45,000 this year may still legitimately claim the enhanced rate based on last year's smaller bill — and one that has shrunk might not realise it now qualifies.

What is the most common payroll mistake?

Not claiming the Employment Allowance in full. It's worth up to £10,500 a year to eligible employers in both 2025/26 and 2026/27, claims can be backdated up to four tax years, and it's missed constantly because it's a single checkbox that doesn't survive a provider switch or a change of staff.

How do I know if my payroll has errors?

Common symptoms include HMRC business tax account demands that don't match your payroll reports, employees querying their tax code or pay, statutory pay reclaims lower than expected, and penalties or specified charges appearing with no obvious cause. A payroll review compares your data against HMRC's records line by line to find the gap.

Can payroll errors be corrected retrospectively?

Usually yes. FPS corrections, backdated Employment Allowance and NI category claims, and statutory pay overpayment reclaims are all possible after the fact, and duplicate employments can be resolved directly with HMRC. The sooner errors are found, the more can typically be recovered before it compounds further.