A salary calculator gives you an annual planning estimate. Your payslip reflects one specific pay period, run through your employer's actual payroll system with your individual payroll information. The two are answering slightly different questions, so a small difference, and sometimes a larger one, is normal rather than a sign that something is wrong.
Annual estimate vs actual payroll
WageOra's calculators work out a single, steady figure for the whole tax year, then divide it into monthly or weekly averages. Real payroll doesn't work that way: it calculates each pay period on its own, using the pay and tax details in place for that period. If your pay or circumstances aren't perfectly even across the year, an averaged annual estimate and one specific payslip won't match exactly, even when both are correct.
PAYE and previous pay
Most PAYE runs on a cumulative basis: what you've already earned and paid in tax so far this tax year can affect this pay period's calculation, spreading your Personal Allowance evenly across the year. Some situations use a non-cumulative or emergency tax code instead, which looks only at the current period in isolation. Either way, this is something an annual estimate can't fully reproduce. See how PAYE works and understanding tax codes for more detail.
Bonuses and overtime
A bonus or a block of overtime often arrives in a single payroll period. There's no separate "bonus tax rate" or "overtime tax rate" — but because Income Tax and National Insurance are worked out on that period's total pay, a one-off extra payment can push part of it into a higher band or a higher National Insurance rate for that period specifically. An annual estimate that compares your income with and without the extra amount won't reflect that in-period concentration. See how a bonus is taxed and how overtime is taxed.
Pension method and pensionable pay
WageOra currently models one disclosed pension arrangement: a net pay contribution taken as a percentage of gross salary. Your employer's actual scheme may define pensionable pay differently, or use a different arrangement such as salary sacrifice or relief-at-source, both of which can affect a payslip differently from WageOra's model. See How WageOra Works for exactly what is and isn't modelled.
Student Loans
Student Loan and Postgraduate Loan repayments are normally worked out per pay period against that period's earnings, not against a smooth annual average. A bonus or irregular pay in one period can therefore change that period's repayment in a way an annual estimate doesn't capture. If you have more than one job, each employer's payroll generally assesses repayments separately, which may not match a combined estimate either.
Other common reasons
- a tax code change during the year
- starting or leaving a job partway through the tax year
- a period of unpaid leave
- irregular or variable hours
- taxable benefits in kind
- statutory payments, such as sick pay or parental pay
- having more than one job
- ordinary payroll rounding
What to check
If a result looks different from your payslip, it can help to check:
- the gross pay shown on the payslip for that period
- your tax code
- the pay period the payslip covers
- any pension deduction shown
- any Student Loan or Postgraduate Loan line
- whether the period included a bonus or overtime
- your year-to-date pay and tax figures, where shown
When to ask someone
If a difference is substantial or you can't account for it, your employer's payroll or HR team can see payslip details that WageOra has no access to. GOV.UK also has a tool to check if the tax on your payslip is correct. WageOra can't diagnose an individual payroll error — it can only show you what an annual estimate looks like using the figures you enter.
See your own estimate
The Salary Calculator gives an annual estimate using WageOra's shared tax engine. See how to read your payslip to match up what's actually on it.