Your payslip arrives, you glance at the bottom line, and you move on. That's how most people read them — and it's how small errors survive for months unnoticed. A payslip is more than a receipt. It records what you earned, what was taken before the money reached your account, and what you might be able to reclaim. Reading one properly takes about five minutes. Those five minutes, repeated every payday, are the difference between catching a mistake early and discovering it a year later when the money is far harder to chase.

What every payslip has to show

Employers must give you a payslip for each pay period. It has to show your gross pay, an itemised list of deductions and your net pay — the amount that actually reaches your bank account. Your name, your employer's name, your National Insurance number and the dates covered should appear too, along with your tax code and NI category letter on most payslips.

Since 2019 this right covers workers as well as employees, so agency and casual staff should receive one, on paper or electronically. Keep them. Payslips are accepted as proof of income for mortgages, tenancy applications and benefit claims, and they are the first thing anyone asks for when your tax record is questioned.

If your employer uses payroll software, you may also see year-to-date figures running down the right-hand side. Treat these as your running scoreboard: they show total pay, total tax and total NI for the tax year so far. If a single month looks odd but the year-to-date column still adds up, you probably have a timing quirk rather than a real problem.

Most payslip errors are small, boring and entirely fixable. The only real mistake is never looking.

Gross pay: rarely just your salary

The payments section at the top is your earnings before deductions. Basic pay is usually the biggest line, but watch for overtime, shift allowances, commission, bonuses, holiday pay and statutory sick pay. Reimbursed business expenses normally appear here too, though genuine costs like train fares are not taxed as earnings.

Gross pay is worked out per pay period, not per year. Someone on £30,000 a year has a monthly gross of £2,500; a month with overtime might show £2,900. Tax and National Insurance respond to that individual payment, which is why take-home pay doesn't rise in a neat straight line when you work extra hours.

This catch is worth understanding properly, because it surprises people every December. If you earn £2,900 in a month instead of £2,500, the extra £400 doesn't simply arrive minus 20% tax. It can tip you into a higher NI band, and if it pushes you over a student loan repayment threshold, that comes out too. Work a run of overtime and your average tax rate creeps up; take a quiet month and it falls again. Your actual annual bill usually evens out across the year, but any single payslip can look harsher than you expect.

Income Tax and the code in the corner

Income Tax is collected through PAYE. Your tax code tells your employer how much you can earn before tax begins. Multiply the number by ten and you get roughly your annual tax-free amount, so 1257L — the most common code — reflects the standard Personal Allowance.

The letters matter. L is the standard allowance; M and N pass allowance between spouses or civil partners under the Marriage Allowance. A K code means you have income that isn't being taxed another way, and the number is added to your taxable pay rather than subtracted. BR taxes everything at basic rate — common on a second job — and D0 or D1 apply higher or additional rates. If you see an X, your code is emergency, which usually means HMRC is waiting for information about a job you've left.

A wrong code is the most common reason for overpaying tax. If your code doesn't match your circumstances — a new job, a second job, a company benefit, a change in the Marriage Allowance — you can check it against your HMRC personal tax account and request a correction. Overpayments are refundable, often for several years back, but only if you ask.

National Insurance: the deduction people ignore

National Insurance is separate from tax and works on its own thresholds. Your category letter tells your employer which rate to apply. Most employees are category A; B applies to married women with a valid reduced-rate election, C to those over State Pension age, and J, L and Z to various deferment situations.

NI is calculated per pay period, not cumulatively like tax. That means two identical salaries paid monthly can produce different NI if one month contains a bonus. It also means NI cannot be refunded in the same neat way as overpaid tax — once it's paid, it stays paid, which is why industrial tribunals and payroll teams treat it carefully.

Check that your NI number is correct on every payslip. One wrong digit and your contributions may land in someone else's record, which can affect your State Pension forecast decades later. It is a genuinely boring thing to check and a genuinely expensive thing to miss.

Pension, student loans and other deductions

Below tax and NI you'll usually find pension contributions, often shown as a percentage and split between your contribution and your employer's. If you were automatically enrolled, your employer must contribute at least 3% of qualifying earnings, and you pay in too unless you opted out.

Student loan repayments appear as a separate line, taken at a percentage of income above the relevant threshold. Plan 1, Plan 2, Plan 4 and postgraduate loans each have their own thresholds and rates, so the same salary can produce different deductions depending on which plan you're on.

You might also see salary sacrifice arrangements, cycle-to-work schemes, childcare vouchers, union subscriptions, or a court order. And if you're paid through an umbrella company, look closely at the employer's NI line — some arrangements push this cost onto you in a way that reduces your headline rate.

Getting to net pay: a worked example

Put it together and the arithmetic is less mysterious. On £30,000 a year paid monthly, you'd see gross pay of £2,500.

• Income Tax at basic rate on the portion above your monthly allowance: roughly £299
• National Insurance at the main rate on earnings above the monthly threshold: roughly £150
• Pension contribution at 5% of qualifying earnings: roughly £100

That leaves a net pay of around £1,951. Change the pension percentage, add a student loan, or pick up a bonus, and every line moves. The point isn't the exact figures — thresholds change — but the shape: gross at the top, deductions in the middle, net at the bottom, and an explanation for every step.

Five things to check every payday

1. Gross pay matches your contract, plus any overtime or holiday pay you're owed.
2. Tax code hasn't changed unexpectedly, and still reflects your actual circumstances.
3. NI letter is correct for your age and status.
4. Pension contributions are being taken at the rate you agreed, and your employer's share is there.
5. Net pay is what you expected, and lands in your account on the right day.

What to do when something looks wrong

Start with your employer's payroll team, not HMRC. Most errors are data entry slips — a missing timesheet, a duplicated deduction, a tax code that didn't update — and payroll can fix them in the next cycle. Raise it in writing and keep the reply with the payslip.

If the error continues, or your employer won't engage, contact HMRC about the tax element and check your personal tax account for your full employment history. If you believe you're owed money, refunds can usually be claimed for up to four years. If it's a pay dispute rather than a tax one — unpaid wages, missing holiday pay, deduction without consent — ACAS can advise on raising a formal grievance or taking it further.

None of this requires you to become an accountant. It requires you to look, compare, and ask one question when a number doesn't make sense. That habit, repeated every payday, is worth far more than the five minutes it costs.

Photo: jarmoluk / Pixabay