NHS Number Validator
Validate NHS numbers with the modulus 11 check and make test numbers.
About this tool
Paste NHS numbers, one per line, with or without spaces. Each is validated with the official modulus 11 algorithm and formatted as 3-3-4. Press the button to generate valid test numbers in the 999 range, which is never issued to patients.
How the NHS number check digit works
Every patient registered with the NHS in England, Wales and the Isle of Man has a 10-digit NHS number. The 10th digit is a check digit calculated with modulus 11. Multiply the first nine digits by 10, 9, 8, 7, 6, 5, 4, 3 and 2, add the results and divide by 11. The check digit is 11 minus the remainder, where 11 becomes 0. If the result is 10, those nine digits are never used. This catches every single-digit error and most transposed pairs, which is why clinical systems validate it on entry. 943 476 5919 is the NHS's published example, and changing its last digit makes it fail. For developers and testers, numbers beginning 999 are reserved for testing and never issued to real patients, so they're safe in demos and test data. Honest limits: a valid check digit doesn't mean a number is in use or belongs to a particular person. Only the NHS Personal Demographics Service (via approved systems) can confirm that. Scotland's CHI numbers and Northern Ireland's H&C numbers use the same check but different ranges. Health identifiers are personal data, so this runs entirely in your browser. Not medical advice. The National Insurance number checker and the check digit calculator are related.
Frequently asked questions
How do I check an NHS number is valid?
Use the modulus 11 check: weight digits 1–9 by 10 down to 2, sum, and 11 minus the remainder is the check digit.
What are NHS test numbers?
Numbers starting 999, which are never issued to patients and are safe for software testing.
Where can I find my NHS number?
On NHS letters, prescriptions and in the NHS App, or ask your GP surgery.
Is my data sent anywhere?
No. Everything is checked in your browser, and nothing is stored, looked up online or sent.