UK Payroll and PAYE: A Complete Guide for Small Business Employers
Reviewed by Usman, Senior Accountant · Route Business Hub · Last reviewed 15 July 2026
Running payroll correctly is a legal reporting obligation with a real-time deadline attached to every single pay run, not an annual task like a tax return. Most of the compliance risk sits in the mechanics employers rarely think about until something goes wrong — RTI submission timing, auto-enrolment thresholds, and benefits-in-kind reporting.
Real Time Information (RTI) — what has to happen on or before every payday
Every UK employer must submit a Full Payment Submission (FPS) to HMRC on or before the date employees are actually paid — not after, which is the single most common compliance slip for small employers running payroll manually or informally (GOV.UK on PAYE reporting (RTI)).
Late or missing FPS submissions trigger automatic penalties that scale with the number of employees and how many times it's happened in the tax year — this isn't a discretionary HMRC decision, it's a formulaic penalty regime.
A separate Employer Payment Summary (EPS) is needed in specific situations — no employees paid in a period, reclaiming statutory payments, or claiming Employment Allowance — and is easy to miss because it isn't part of every routine pay run the way FPS is.
A worked example: Employment Allowance on a small payroll
Employment Allowance for 2026/27 is £10,500 — an eligible small employer can reduce their employer Class 1 National Insurance bill by up to that amount across the year, claimed via the EPS rather than applied automatically.
A business with an annual employer NI bill of £8,000 that's eligible but never claims it simply pays the full £8,000 — the allowance only reduces what's owed if it's actively claimed, which is exactly the kind of easy-to-miss step this guide flags above.
Auto-enrolment: who has to be enrolled, and when the thresholds actually bite
Every employer must assess each employee's auto-enrolment status at every pay run, not just once when they join — an employee's age and earnings can move them in or out of the automatic enrolment criteria as their pay changes.
The earnings trigger and the qualifying earnings band are two different things: an employee needs to earn above the trigger to be automatically enrolled, but minimum contributions are calculated on a separate band of qualifying earnings — conflating the two is a common source of underpaid pension contributions.
Re-enrolment happens automatically every 3 years for eligible staff who previously opted out — missing this cycle is a compliance gap employers frequently don't realise exists until it's flagged.
PAYE, National Insurance, and what actually gets deducted from each payslip
Income tax is calculated using each employee's tax code against the relevant bands — an incorrect tax code, common after a job change, multiple jobs, or a P45 issue, directly under- or over-deducts tax every pay run until it's corrected.
Employee and employer National Insurance are calculated separately, with different thresholds. Employment Allowance can reduce the employer NI bill for eligible small employers, but has to be actively claimed via the EPS, not applied automatically.
Statutory payments — sick pay, maternity, paternity, adoption pay — have their own eligibility rules and reclaim mechanisms, and getting the qualifying conditions wrong means either underpaying an employee's statutory entitlement or the business not reclaiming what it's owed.
Benefits in kind and P11D — the part employers most often get wrong
Anything provided to an employee beyond salary — a company car, private medical insurance, an interest-free loan over the threshold — is potentially a benefit in kind, reported either via P11D after the tax year or payrolled in real time if registered to do so before the tax year starts.
Payrolling benefits has to be set up with HMRC in advance — you can't decide partway through a tax year to start payrolling a benefit you didn't register for at the start of it.
Class 1A National Insurance on benefits in kind is a separate employer-only charge, reported and paid annually, and is often the line small employers forget entirely when budgeting the true cost of a benefit they're providing.
This is general information, not personalised advice — tax treatment depends on your specific circumstances, and rates and thresholds shown here can change. Talk to us before acting on your own position.
Want the short version now? Our UK Payroll Wind-Down & PAYE Compliance page covers the core of this today.
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