API / Payroll
Payroll calculation API
Short answer
One pay period exactly as payroll software runs it: tax on a cumulative or week 1/month 1 code, employee and employer NI by category letter (directors on the annual earnings period), student loans and the NI earnings bands for RTI.
- HMRC’s 2026/27 payroll test cases for income tax, NI, directors’ NI and student loans run through this endpoint, to the penny.
- All 16 NI category letters, Freeport and Investment Zone ones included.
Endpoints
POST /v1/payroll/periodTax, NI and student loans for a periodGET /v1/ratesEvery rate and threshold (no key)
Try a request
Money is pounds and pence. Every response carries the tax year, the engine and HMRC test data that produced it, the assumptions and the gov.uk sources.
curl https://api.checktakehomepay.co.uk/v1/payroll/period \
-H "Authorization: Bearer $CHECKTAKEHOMEPAY_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"pay_frequency": "monthly",
"period": 1,
"tax_code": "1257L",
"gross_pay": 3000
}'Questions
Can I use it instead of a payroll tax table?
Yes: it follows HMRC’s PAYE tax table routines and NI guidance for software developers, and passes HMRC’s own test cases.
Put it in your software
Every endpoint on every plan, from the free one up.