Methodology
The complete calculation, in the order it happens, with the rule behind each step. If you disagree with a figure, this page should let you find exactly where we differ.
The Order of Operations
Order matters. Applying the same rules in a different sequence gives a different answer, and most disagreements between pay calculators come from sequence rather than from the rates.
- Basic pay — the annual figure for your band and step, multiplied by your hours divided by the nation's standard week.
- High Cost Area Supplement — England only. The percentage applies to full-time basic pay, is clamped to the annual minimum and maximum, rounded up to the whole pound, and only then pro-rated for part-time hours.
- Unsocial hours — Section 2 enhancement on your hourly rate for the hours actually worked at those times.
- Other pay — added as entered, not pensionable.
- Salary sacrifice — deducted before everything else, reducing gross and pensionable pay.
- Pension contribution — the tier rate applied to actual pensionable pay.
- Income tax — on gross minus pension.
- National Insurance — on gross, without deducting pension.
- Student loans — on gross above each plan's threshold. Plans stack.
The Pension Tier Rule
Your contribution rate is tiered, and the tier is set by your actual pensionable pay, not the whole-time equivalent salary of your post. This changed on 1 October 2022. Applying the old rule pushes part-time staff into a higher tier than they belong in, and it is still commonly reported incorrectly.
Three administrators run different tier tables: NHSBSA for England and Wales, SPPA for Scotland, and HSC Pension Service for Northern Ireland. The calculator picks the right one from the nation you select.
| Administrator | Tiers | Range | Employer Rate |
|---|---|---|---|
| NHS Business Services Authority (England & Wales) | 6 | 5.2% to 12.5% | 23.7% |
| Scottish Public Pensions Agency | 9 | 5.7% to 12.7% | 22.5% |
| HSC Pension Service (Northern Ireland) | 6 | 5.2% to 12.7% | 23.2% |
The Net Pay Arrangement, and Its Limit
Contributions are taken under a net pay arrangement: deducted before income tax, so relief is immediate at your marginal rate. National Insurance works differently. NI is charged on gross pay and the pension contribution does not reduce it. Any calculator that deducts pension before computing NI will understate your NI and overstate your take-home.
The same is true of student loans: they are assessed on the same base as NI, so pension contributions do not reduce them either.
NI is also charged on each pay period, not on the year. Income tax is cumulative; NI is not. HMRC publishes a monthly primary threshold of £1,048, which is £12,570 rounded to the nearest pound rather than divided exactly, so twelve monthly charges come to about 48p a year less than one annual calculation. We use the monthly basis, because that is what appears on a monthly payslip. A calculator working annually will be a few pence out for every NHS employee.
High Cost Area Supplement
England only, and the caps bite at both ends. A band 2 in Inner London receives the minimum, worth more than 20% of basic pay; a band 9 receives the maximum, worth much less. Applying a flat percentage is wrong in both directions.
The published supplement is a whole-pound figure rounded up. We verified that against all 435 basic-plus-HCAS totals published in the England pay-scale tables: rounding up reproduces every one, plain rounding misses 36 of them by £1.
Split National Insurance Years
Rates or thresholds moved mid-year in 2022/23 and 2023/24. Each period is applied to your annual pay and weighted by the share of the year it covered. Real payroll assesses NI separately in each pay period, so a split year is an approximation and is flagged as an assumption on the result.
Every Assumption We Make
| Assumption | What It Means |
|---|---|
| Tax code 1257L | The standard code giving the full personal allowance. A different code changes your tax. |
| Paid evenly all year | Figures assume 12 equal monthly payments. Arrears, bank shifts and variable enhancements move individual payslips. |
| No salary sacrifice | Lease cars and cycle schemes reduce gross pay before every other deduction and are not modelled. |
| No taxable benefits | Benefits in kind reported on a P11D are not modelled. |
| Enhancements pensionable | Basic pay, HCAS and unsocial hours are pensionable, as set out in the AfC handbook. Other pay you enter is treated as non-pensionable. |
| Pension tier on actual pay | Your contribution tier is set by actual pensionable pay — the rule since 1 October 2022 — not by whole-time equivalent. |
| Blended National Insurance | National Insurance rates changed part-way through this tax year. We apply each rate weighted by the part of the year it covered; real payroll assesses NI separately in each pay period, so your actual total will differ a little. |
| Sacrifice cuts pensionable pay | Salary sacrifice is treated as reducing your pensionable pay as well as your gross, which is the normal treatment for lease cars and similar schemes. Buying additional pension works differently — check your own arrangement. |
| Step, not years of service | Pay steps are shown as entry, mid and top. You choose your step rather than your start date, so the calculator cannot check you are on the right one: the published minimum is two or three years on each step, or five for bands 8a to 9 in Scotland. |
What Is Deliberately Not Modelled
- Emergency or adjusted tax codes beyond the standard forms the calculator recognises
- Benefits in kind reported on a P11D
- Additional voluntary contributions and added pension purchase
- Bank shifts and overtime paid at plain time
- The distorted PAYE treatment of a single large arrears payslip
- Pension annual allowance and lifetime tax charges
- Marriage allowance and the high income child benefit charge
- Local deductions — car parking, union subscriptions, staff schemes
- The 1995 and 2008 legacy pension schemes, and the 50/50 option
Rounding
Calculations run at full precision and are rounded only for display. Student loan repayments use whole pounds above the threshold, as they are actually assessed. Monthly figures are the annual figure divided by twelve; real payroll rounds each month independently, so individual months differ by pence.
Hourly Rates
Hourly = annual ÷ (standard weekly hours × 52.143). Scotland's standard week is 36 hours from April 2026 and 37 before, which is why its hourly rates are higher relative to the annual figure.
Where a published hourly rate does not reconcile with its own annual figure, we use the annual figure — pay is set annually — and record the discrepancy rather than silently choosing one. There are currently none. See the sources page.
How This Is Tested
The engine runs against a golden corpus of hand-worked cases plus cross-checks against figures published in the source data. The strongest of those is the HCAS check described above, because it compares our arithmetic against numbers produced independently by the publisher. See how we verify.