API Reference
Last updated: March 2026 · Changelog · OpenAPI spec · Postman collection
POST
/api/v1/calculateFreeCalculate taxes
Calculate household employer taxes for a single pay period. Returns employer taxes, employee tax estimates, per-paycheck cost, and threshold status.
Note: Free-tier calculations assume zero year-to-date wages. Mid-year, this may overstate Social Security (caps at $176,100 wage base) and FUTA (caps at $7,000/employee). For accurate ongoing calculations, upgrade to a paid plan with automatic YTD tracking.
Required scope: calculator
Parameters
| Name | Type | Required | Description |
|---|---|---|---|
| state | string | Yes | 2-letter US state code |
| annual_wages | number | Yes | Annual wages (0-999,999) |
| pay_frequency | string | No | weekly, biweekly, semimonthly, monthly. Default: biweekly |
| filing_status | string | No | single, married, head_of_household. Default: single |
POST calculate
{
"state": "CA",
"annual_wages": 35000,
"pay_frequency": "biweekly",
"filing_status": "single"
}