Methodology

Where the rates come from

The National Joint Council publishes a pay circular each year carrying the full spine: an annual salary and an hourly rate for every spinal column point. We transcribe both columns. We never derive one from the other, and we never apply the award percentage to last year’s figures — the 2025 circular had to be reissued because of hourly-rate rounding, which is precisely the error deriving introduces.

The award percentage is used for one thing: checking the transcription. Every annual figure must reconcile with the previous year under the declared award to within £1, and every hourly figure must follow from its annual by the NJC formula to within a penny. A row failing either check stops the build.

How a table is verified

A table is imported once by script from the circular’s own text layer. That single pass is never enough to call it verified. A second, independent extraction reads the same PDF by glyph geometry — word coordinates rather than reconstructed columns — and every value must agree. The PDF is pinned by SHA-256. A record is only marked verified once a named person has also confirmed the document is the circular it claims to be, and the build refuses to publish a table that has not been re-verified within 120 days.

The calculation

Everything is held in whole pence. Each figure is rounded once, half-up, at the end.

increase = new annual (full-time) − old annual (full-time)
share    = your hours ÷ full-time hours  [× paid weeks ÷ 52.143 if term-time-only]
monthly  = increase × share ÷ 12
arrears  = increase × share × months owed ÷ 12
total    = arrears + monthly

Months owed runs from April — or the month you started, if later — to the month before the new rate first appears in your pay. If it appears in October, that is April to September: six months. If it appears in April there are no arrears, just the uplift.

Worked example

SCP 12, 18.5 hours on a 37-hour week, new rate first appearing in October 2026:

SCP 12 rose from £28,598.00 to £29,542.00. Note that six times the monthly figure is not exactly the arrears figure — each is rounded once from full precision, rather than one being multiplied out from the other. Your payroll may round along a different path again, so a difference of a few pence is normal.

The NHS tables, which are read differently again

Agenda for Change is not one document. Each nation publishes its own circular, in its own shape, and the four disagree in ways that matter: Scotland runs a 36-hour week from April 2026 where the others run 37.5, Northern Ireland charges more pension than England on identical bands, and Wales lifted its lowest pay points to the Living Wage instead of giving them the award. Nothing is ever carried across from one nation to another. Where a figure is not held for a nation, the page says so rather than borrowing a neighbour’s.

Two circulars needed readers of their own. The Welsh table wraps a cell onto the following line, where a line-ordered parser cannot tell which column an orphan number belongs to, so it is read by glyph geometry. The Scottish circular prints rates in one annex and progression in another, and the 2025-26 table sets the superseded figures one column to the left of the payable ones — so the import config names every column, and the reader takes the rate from the column declared to hold it. Both annexes are parsed separately and must agree before anything is written.

Tax, National Insurance and pension

These are rules rather than lists, so the shape matters as much as the numbers. Income tax and National Insurance are marginal — each rate applies only to the slice of income inside its own band. The NHS and HSC pension schemes are not: the tier your pensionable pay falls into sets one rate, and that rate is charged on all of it. That is settled by regulation 30 of the NHS Pension Scheme Regulations 2015, not inferred, and it is why a pay rise crossing a tier boundary can cost more than the rise is worth.

A pension table cannot exist here without declaring which basis it uses and quoting the wording that establishes it. There is no default, because a wrong guess moves a member’s contribution by hundreds of pounds a year.

National Insurance is worked out on the monthly thresholds rather than the annual ones. They are not the same figure: HMRC publishes £1,048 a month and £12,570 a year, and twelve times £1,048 is £12,576. NI is charged on each pay period in isolation, so the monthly figure is what payroll actually applies. Using the annual one makes every take-home figure wrong by pence, and this site was wrong by pence until a comparison against another calculator found it.

Where these figures cannot be re-read by a second extraction — an HTML page rather than a PDF — they are instead re-derived from the rule that generates them. Every NHS pension threshold is reproduced from the legislated figures by regulation 30(7)’s own indexation rule, September CPI rounded up to the nearest pound. A check that regenerates a number is stronger than one that reads it twice.

What this will not do

• Guess a date. If your employer has not stated when the uplift will be paid, the tool says so rather than assuming a month.
• Go beyond the published table. A point that is not on the imported spine is refused, not extrapolated.
• Present provisional figures as final. A table that has not completed verification renders with a flag on every page that uses it.
• Estimate take-home pay. All figures are gross. Tax, National Insurance and pension come off.

What the estimate excludes

Allowances, enhancements, overtime, sleep-ins, any increment you moved through during the period, and the effect of a payroll cut-off, which can shift either component by a month.

Every result carries its version

A printed result names the engine version and the identity, status and verification date of both spine tables behind it. If a table is later corrected, the old result can still be reproduced and the difference explained. Corrections are logged at /corrections.