Most people glance at the bottom line of a payslip, confirm the number looks roughly right, and file it. That habit hides the two or three lines that decide whether the figure is correct — and payroll errors are rarely dramatic. They are small, repeated, and they cost the same amount every month for as long as nobody notices.
Gross pay is a promise, net pay is the delivery
Gross pay is the total your employer says it owes you for the period: base salary, overtime, shift allowance, commission, bonuses, paid leave. Net pay is what reaches your account after every deduction. Everything between those two numbers should have a label, and every label should map to something you agreed to or something the law requires. If a line has no label you recognise, that is the first thing to question — not the total.
The period the slip covers is the first thing to check before anything else. A slip dated for a month in which you joined or left partway through, took unpaid leave, or received a backdated raise will legitimately differ from the previous one, and comparing it to last month without that context makes a correct slip look wrong.
The statutory deductions you cannot opt out of
Income tax is normally the largest line. What matters is not the amount but the basis: is it calculated on this period’s pay, or on a projected annual figure? A one-off bonus can push a single period into a higher band, so a bigger-than-usual deduction in a bonus month is often arithmetic rather than error. Social insurance or national insurance contributions are usually a percentage with a ceiling; if the percentage jumps without a salary change, ask which cap applied.
Where an employer operates pay-as-you-earn withholding, the annual reconciliation is what settles the final figure. That is why a refund or a small additional charge sometimes appears months later. The mechanics of withholding are explained at IRS.gov for anyone who wants to see how a withholding table turns gross pay into a tax figure.
Voluntary deductions: read the ones you signed
Pension contributions, medical cover, life insurance, union dues, loan repayments, salary advances, childcare vouchers, gym subsidies. These are the lines most likely to drift, because they are set once and forgotten. A pension percentage that was correct at your old salary is wrong after a raise, and a loan repayment that should have ended three months ago will happily keep running.
For each voluntary line, ask three questions: did I agree to this, is the amount still the one I agreed to, and does it have an end date? If the answer to the third is yes and the date has passed, you are owed money.
Employer contributions are real money, but not yours yet
Many slips show an employer pension contribution separately, sometimes in a section headed “employer costs”. That figure is not deducted from your pay and will not appear in your net. It is still worth checking, because it is genuinely part of your compensation and it is easy for an employer to underpay it quietly. If the slip shows an employer percentage, confirm it matches your contract.
Five errors worth checking every single month
- Overtime hours — compare against your own record, not the shift roster. Rounding rules favour the employer more often than not.
- Tax code or band — a wrong code is invisible on the slip unless you know what it should be.
- Unpaid leave — deducted twice is a common payroll glitch after a system migration.
- Expense reimbursements — these should not be taxed. If a reimbursement appears inside gross pay, you have been taxed on money you spent for work.
- Duplicate deductions — two identical insurance or loan lines in the same period usually means a stale record, not double cover.
A two-minute monthly routine
Keep a folder — paper or a phone album — with every slip in date order. Once a month, compare this slip with the last one line by line and write down anything that moved by more than a rounding amount. Two minutes of comparison catches nearly everything, and a written trail makes the conversation with payroll short and factual rather than a vague complaint.
If a deduction turns out to be wrong, raise it in writing within the pay period if you can, quoting the line label and the amount. Payroll teams can usually correct the current period; corrections to older periods require a manual adjustment, which is slower and sometimes simply refused after a year.
The same discipline pays off beyond the slip itself. Once you know your true net figure, budgeting stops being guesswork — building a simple budget that actually works starts from exactly that number, and cutting avoidable bank fees and building an emergency fund on a tight budget both get easier when the income figure is one you trust.