Check NHS identifier control digits.
Initialising algorithm engine for NHS Number Check Digit Calculator...
How NHS Number Check Digit Calculator Works?
The NHS Number Check Digit Calculator works by multiplying the first 9 digits of a National Health Service (NHS) number by weights 10 down to 2, dividing the sum by 11, and subtracting the remainder from 11.
- 1Enter the first 9 digits of the 10-digit NHS number.
- 2Multiply the digits by 10, 9, 8, 7, 6, 5, 4, 3, and 2.
- 3Total the 9 NHS products and find the remainder after division by 11.
- 4Subtract the remainder from 11; a result of 11 becomes 0.
- 5Reject the payload when the result is 10: no valid NHS number exists for it.
NHS Number Check Digit Calculator Formula
The NHS number formula is Check = 11 − (Σ (11 − i)·dᵢ mod 11), with 11 → 0 and 10 → invalid.
S = 10·d₁ + 9·d₂ + … + 2·d₉ Check = 11 − (S mod 11); 11 → 0; 10 → invalid
dᵢis the i-th digit.
9×10 + 4×9 + 3×8 + 4×7 + 7×6 + 6×5 + 5×4 + 9×3 + 1×2 = 299 299 mod 11 = 2 Check = 11 − 2 = 9 → 9 NHS number = 943 476 5919
NHS Number Check Digit Calculator Conversion Table
The NHS number conversion table lists sample payloads with their check digit, including an invalid case.
| Payload (9 digits) | Weighted sum | S mod 11 | Check | NHS number |
|---|---|---|---|---|
| 943476591 | 299 | 2 | 9 | 943 476 5919 |
| 401023213 | 92 | 4 | 7 | 401 023 2137 |
| 999123456 | 320 | 1 | invalid | None |
| 485777345 | 312 | 4 | 7 | 485 777 3457 |
| 123456789 | 210 | 1 | invalid | None |
| 000000001 | 2 | 2 | 9 | 000 000 0019 |
What is NHS Number Check Digit Calculator?
An NHS Number Check Digit Calculator is a tool that computes or validates the 10th digit of a National Health Service number used in England, Wales, and the Isle of Man.
About 1 in 11 nine-digit payloads produces a check value of 10, and the NHS never issues those numbers. Scotland uses the Community Health Index (CHI) number with the same modulus 11 check.
What are the uses of NHS Number Check Digit Calculator?
There are 3 main uses of the NHS Number Check Digit Calculator, including patient registration, record matching, and test data.
- Patient registration: GP and hospital systems validate NHS numbers on entry.
- Record matching: Data teams flag invalid NHS numbers before linking records.
- Test data: Developers use NHS test ranges (starting with 999) for software testing.