Payroll looks simple until the first month something goes wrong. A wrong tax code, a late submission, a missed pension deadline, and suddenly you have unhappy staff, an HMRC letter and a penalty that costs more than the mistake itself.
Most payroll mistakes UK small businesses make are not deliberate. They happen because payroll is treated as a quick monthly job rather than an ongoing responsibility with strict rules and deadlines. The problem is that HMRC treats late or incorrect payroll seriously, and employees notice fast when their pay is wrong.
Here are the ten payroll mistakes that cause the most trouble for UK employers, and what to do differently.
1. Missing RTI Submission Deadlines
Under Real Time Information, you have to report payroll to HMRC on or before the day you pay your employees. Not at month-end. Not when you get around to it. On or before payday.
This is the single most common payroll slip. A business runs the pay, transfers the wages, and files the Full Payment Submission a few days later because nobody realised the deadline was payday itself. HMRC can charge late filing penalties for this, and they add up across the year if it keeps happening.
Set your payroll date a day or two before payday so the submission always goes in first. If you run payroll manually and the deadline keeps sliding, that is usually the sign it needs handing off. Aspire's payroll and PAYE support covers RTI submissions so the deadline is never something you have to remember.
2. Using the Wrong Tax Code
An employee on the wrong tax code either pays too much tax or too little. Both cause problems. Overpaying frustrates staff. Underpaying means they get a bill later, and they rarely blame HMRC for it, they blame the employer who ran the payroll.
Wrong codes usually creep in when a new starter joins without a P45, when HMRC issues a code change that never gets applied, or when someone stays on an emergency code for months. Check every code change HMRC sends and apply it in the next pay run, not three months later.
3. Getting New Starters and Leavers Wrong
New starters need the right information from day one, ideally a P45 from their last job or the correct starter declaration if they do not have one. Skip this and they often land on an emergency tax code straight away.
Leavers are just as easy to mishandle. Forgetting to issue a P45, or leaving someone on the payroll after they have gone, creates reporting errors that follow you into year-end. Process starters and leavers properly the moment they join or leave, not in a catch-up session later.
4. Missing Pension Auto-Enrolment Duties
Auto-enrolment is not optional, and it is not a one-off task. If you employ staff who meet the criteria, you have duties around enrolling them, making contributions, and re-enrolling eligible employees every three years.
Many small businesses set up their pension scheme once and then forget the ongoing duties, especially re-enrolment and the declaration of compliance. The Pensions Regulator can take action where duties are ignored. Treat auto-enrolment as a recurring responsibility, not something you handle once and file away.
5. Miscalculating Statutory Payments
Statutory sick pay, maternity pay, paternity pay and other statutory payments each have their own rules and rates. Getting the eligibility or the amount wrong means either underpaying an employee who is entitled, or overpaying and struggling to recover it.
These situations do not come up every month, which is exactly why they trip people up. When an employee goes off sick long-term or announces a pregnancy, that is the moment to check the current rules carefully rather than guessing from what you remember happening last time.
6. Confusing Director Salary With Dividends
For limited company directors who pay themselves, payroll and dividends are two separate things. Salary goes through payroll with PAYE where it applies. Dividends come from company profits after Corporation Tax and need their own paperwork.
Mixing the two up, or running director pay through payroll incorrectly, creates problems for both the company records and the director's personal tax. This is one of those areas where a small habit of recording things properly saves a lot of untangling at year-end. There is more to say about how directors should balance the two, but salary versus dividends is a topic of its own.
7. Not Keeping Proper Payroll Records
Payroll is not just about paying people. You need to keep records of pay, deductions, payslips, RTI submissions, pension contributions, and year-end documents like P60s.
When records are scattered or incomplete, year-end payroll becomes a scramble, and any HMRC query becomes far harder to answer. If HMRC asks how a figure was calculated and you cannot show the working, that is a weak position to be in. Keep payroll records organised throughout the year so year-end is a review, not a reconstruction.
8. Leaving Payroll Until the Last Minute
Rushed payroll is where errors live. When the pay run is squeezed into the final hour before payday, that is when wrong hours get entered, deductions get missed, and submissions go in late.
Payroll needs a proper slot in the calendar, run the same way each period, with enough time to check the numbers before anything is submitted or paid. Employees expect their pay to be right and on time, every time. That consistency is hard to deliver when payroll is always an afterthought.
9. Forgetting Employer National Insurance and Year-End Duties
Employer National Insurance is a real cost that some new employers overlook when budgeting for staff. On top of that, year-end brings its own duties, including issuing P60s to employees and making sure final submissions are correct.
Businesses that treat payroll as a monthly-only task often get caught out by these periodic obligations. Build the year-end steps into your payroll routine so they are not a surprise every spring.
10. Trying to Run Everything Alone as You Grow
One or two employees is manageable for most owners. But as the team grows, payroll gets more complex fast, more starters and leavers, pension duties, statutory payments, varied hours, and tighter margins for error.
The point where payroll starts eating your time or causing repeated mistakes is the point where professional support pays for itself. Getting payroll wrong costs money in penalties and costs trust with your staff, and both are harder to fix than to prevent. If payroll has become a monthly source of stress, talk to ASPIRE UK TAX ACCOUNTANTS about taking it off your plate.
Keeping Payroll Right
Most payroll mistakes come down to two things: missing a deadline, or getting a calculation wrong. Both are avoidable with a proper routine, current knowledge of the rules, and organised records.
If your business is spending too long on payroll, or you have already had an HMRC letter about it, professional payroll support can take the pressure off and keep you compliant. ASPIRE UK TAX ACCOUNTANTS is an ACCA registered UK practice helping sole traders, limited companies and SMEs with payroll, PAYE, pension auto-enrolment, bookkeeping, VAT, tax and HMRC support.
