Why payroll mistakes are more expensive than they look
Get an invoice wrong and you send a corrected one. Get payroll wrong and you have potentially underpaid someone's wages, misreported their tax position to HMRC, miscalculated a pension contribution that has legal minimums attached to it, and created a correction that has to flow through the following month's figures as well as the original one. Payroll errors compound in a way that most other business mistakes do not, because each pay run builds on the figures from the last one, and an error in March does not just affect March, it distorts every subsequent month until it is properly corrected, and it can distort an employee's own tax return if it is not caught before year end.
Employers who have never run payroll before consistently underestimate this. It looks, from the outside, like a monthly arithmetic exercise. In practice it is a compliance function with legal minimums, statutory deadlines and an audit trail that HMRC, and increasingly employees themselves through their personal tax accounts, can and do check.
Real Time Information, and the deadline that catches new employers out
Every employer operating PAYE must submit a Full Payment Submission to HMRC on or before the day employees are actually paid, not the day payroll is processed and not the day after payday. This is the single most common early mistake among new employers, who assume the submission deadline is tied to when they run the numbers rather than when the money actually leaves the business. If your pay date is the last Friday of the month, your FPS needs to reach HMRC on or before that Friday, every single time, and persistent lateness triggers the same points based penalty system that now applies across most HMRC compliance areas, where the consequences build silently before a financial penalty actually lands.
An Employer Payment Summary is a separate, related submission needed in months where you need to tell HMRC about something that is not covered by the FPS itself, statutory pay recoverable from HMRC, for example, or a period where no employees were paid at all. Missing an EPS when one was needed is a quieter mistake than missing an FPS, because there is no immediate visible consequence, but it distorts what HMRC believes you owe and creates a reconciliation headache months later when the figures do not match.
Getting new starters set up correctly from day one
The new starter checklist, which replaced the old P46 process, exists specifically for situations where a new employee cannot provide a P45 from their previous employer, whether because they are starting their first job, coming from self employment, or simply have not received their P45 in time. Getting this wrong, most commonly by defaulting everyone onto the same tax code without properly working through the checklist questions, is one of the more common sources of underpaid or overpaid tax that surfaces months later, usually when the employee's own tax code notice from HMRC does not match what payroll has been using, and by that point several months of incorrect deductions need unwinding.
Good payroll software walks you through this properly rather than leaving it to memory, prompting for the right information at the point a new starter is added rather than relying on whoever runs payroll that month to remember the correct process from the last time they did it, which might have been a year ago.
Statutory payments, and where the calculations actually go wrong
Statutory sick pay, statutory maternity pay, paternity pay and adoption pay all have specific eligibility rules, average weekly earnings calculations and payment periods that are genuinely easy to get wrong by hand, particularly for an employee with irregular hours or a recent change in pay rate. The average weekly earnings calculation in particular uses a specific reference period that does not always align neatly with your normal pay cycle, and a manual calculation error here is one of the more common reasons employees end up underpaid during periods of genuine vulnerability, sickness or new parenthood, which is exactly when the trust between employer and employee matters most and exactly when an error is least forgivable.
This is an area where software genuinely earns its cost. A properly configured payroll system calculates these figures automatically based on the correct reference periods and current statutory rates, and flags eligibility questions rather than assuming a competent human will remember every rule correctly under time pressure at the end of a busy month.
Pension auto enrolment, still misunderstood years after it became mandatory
Every employer has automatic enrolment duties from the day they take on their first member of staff, and those duties do not go away just because a business is small. Eligible workers must be assessed at every single pay run, not just when they join, because someone who does not initially qualify due to age or earnings can become eligible later as their pay changes, and failing to reassess them and enrol them at that point is a compliance breach regardless of whether it was deliberate.
The minimum contribution levels, currently split between employer and employee contributions, are a legal floor, not a suggestion, and The Pensions Regulator does actively check compliance, including through data matching with HMRC submissions, meaning a discrepancy between your payroll figures and your pension contributions is genuinely likely to be noticed, not just theoretically possible. Re enrolment, which happens roughly every three years and requires reassessing staff who previously opted out, is the specific step that catches out employers who set up auto enrolment correctly the first time and then forgot it was not a one off task.
Year end, P60s and the reconciliation that reveals every small error
P60s must be issued to every employee still on the payroll at the end of the tax year, by the end of May following that tax year, and this document matters more to employees than most employers appreciate, since it is frequently required for mortgage applications, tax credit claims and their own self assessment if they have other income. Year end is also the point where small errors accumulated across twelve months of pay runs tend to surface, an incorrect tax code applied for several months, a statutory payment calculated on the wrong reference period, a pension contribution that was never actually corrected after an earlier payroll error.
Employers who reconcile monthly, checking that what was reported to HMRC matches what was actually paid and deducted, tend to sail through year end because there is nothing left to find. Employers who only look properly once a year, at year end itself, often discover several small discrepancies simultaneously, each individually minor but collectively requiring a genuinely time consuming correction process across multiple employees and multiple months.
National minimum wage compliance, which trips up more employers than people realise
National minimum wage breaches are more common than most employers assume, and they rarely happen through a deliberate decision to underpay. The typical cause is far more mundane, an employee whose hourly rate technically meets the minimum wage but who is required to wear a uniform they must purchase themselves, effectively reducing their pay below the legal minimum once that deduction is accounted for, or an apprentice who moves onto the standard minimum wage rate on their birthday but whose payroll record is not updated promptly. HMRC actively enforces this, and being named for a minimum wage breach carries a reputational cost well beyond the financial penalty itself, since the list of named employers is published and picked up by local press with some regularity.
Choosing between running payroll yourself, using a bureau, or software that does both
For a small number of employees, modern payroll software genuinely makes running payroll in house realistic for someone without formal payroll training, guiding you through the pay run in a small number of steps and handling the calculations and submissions that used to require specialist knowledge. As headcount grows, or if your business has genuinely complex arrangements, multiple sites, varying shift patterns, salary sacrifice schemes, the calculation becomes less clear cut, and a payroll bureau or a more sophisticated system becomes worth the additional cost simply for the reduction in personal liability if something goes wrong. There is no universally right answer here, only a right answer for your specific complexity and risk appetite, and the honest test is whether you could explain, off the top of your head, why last month's payroll figures were what they were. If you could not, that is worth taking seriously regardless of how many staff you employ.
Salary sacrifice arrangements, and where they quietly go wrong
Salary sacrifice schemes, most commonly used for pension contributions, cycle to work schemes and increasingly electric vehicle leasing, offer genuine tax and national insurance advantages for both employer and employee, but they need to be set up and maintained correctly to actually deliver those advantages. The employee must genuinely give up the right to the sacrificed salary, not simply have it relabelled, and the contractual change needs to be documented properly rather than assumed. A common error is allowing an employee's contractual salary to drop below the National Minimum Wage once a sacrifice is applied, which is not permitted regardless of how enthusiastic the employee is about the scheme, and payroll software that does not check this automatically leaves the employer exposed to a compliance breach that only surfaces during an inspection, often years after the arrangement was set up.
Another common error is failing to properly adjust a salary sacrifice arrangement when an employee's circumstances change, a reduction in hours, a period of unpaid leave, or a change in the underlying benefit itself. Arrangements that were compliant at setup can drift out of compliance silently if nobody revisits them, which is exactly the kind of ongoing maintenance that a good payroll system should prompt for rather than leaving to institutional memory.
What to do when you discover a historic payroll error
Every payroll function eventually finds an error from a previous period, whether that is a wrongly calculated statutory payment, a pension contribution based on the wrong pensionable pay figure, or a tax code that was applied incorrectly for several months before anyone noticed. The instinct to quietly correct it in the current period and move on is understandable but usually wrong. HMRC has specific processes for correcting Full Payment Submissions retrospectively, and pension contributions typically need a formal correction submitted to the pension provider rather than simply adjusting a future contribution to compensate.
The employee also deserves a clear, honest explanation of what went wrong and how it is being fixed, since payroll errors affecting someone's take home pay or their pension are not abstract accounting adjustments to the person on the receiving end, they are money that affects their actual life. Employers who handle these conversations transparently and promptly tend to retain trust even after a genuine mistake, while those who quietly fix figures without explanation tend to have the error discovered by the employee first, which damages trust considerably more than the original mistake ever did.
Keep a written record of every correction made, what caused it, what was changed, and when, since this record is exactly what a HMRC compliance check or an internal audit will ask to see, and a business that can produce a clear, documented trail of how errors were identified and fixed looks considerably more credible than one that can only describe the process from memory.
A monthly checklist that keeps you out of trouble
Check for any new starters or leavers and make sure their records are complete before the pay run, not after. Confirm any changes in pay rate, hours or benefits have actually been entered rather than assumed to have carried over. Run the pay calculation and review it against the previous month for anything that looks unexpectedly different, since software flagging an anomaly is only useful if someone actually looks at the flag. Submit your Full Payment Submission on or before payday, every time, without exception. Reconcile pension contributions against payroll deductions rather than assuming they match. And keep a simple record of what changed and why each month, because that record is what makes year end reconciliation a formality instead of an investigation.
