> An API for contractors and the self-employed: Class 4 NI, a director’s salary and dividends, umbrella company pay and inside against outside IR35.

Web version: https://checktakehomepay.co.uk/contractor-tax-api · Last updated: 2026-10-09

[API](https://checktakehomepay.co.uk/api) / Contractors

# Contractor and self-employed tax API

Short answer

Self Assessment for a sole trader, a director paid from their own company (corporation tax with marginal relief, dividend tax), an umbrella company’s pay from a day rate, and the same contract inside and outside IR35.

-   Dividends are taxed at 10.75%, 35.75% and 39.35% after the £500 allowance, in the UK bands.
-   Umbrella pay is the largest salary whose employment costs fit what the margin leaves.

## Endpoints

-   `POST /v1/self-employed`Income tax, Class 4 and student loans
-   `POST /v1/director-pay`Salary and dividends from your company
-   `POST /v1/umbrella-pay`Inside IR35 through an umbrella
-   `POST /v1/ir35-compare`Umbrella against limited company

## 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/ir35-compare \
  -H "Authorization: Bearer $CHECKTAKEHOMEPAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "region": "england",
  "income": {
    "amount": 500,
    "per": "day"
  },
  "margin": {
    "amount": 25,
    "per": "week"
  }
}'
```

## Questions

### Which salary does director pay choose?

Give a salary, or leave it out and it tries the usual ones (none, the secondary threshold, the lower earnings limit, the primary threshold) as far as the profit can pay them, with the rest as dividends.

## Put it in your software

Every endpoint on every plan, from the free one up.

[Get an API key](https://checktakehomepay.co.uk/login)[Read the quickstart](https://checktakehomepay.co.uk/docs/quickstart)