Developers and API

JSON API

Every calculator has three endpoints. Inputs you leave out use the calculator’s defaults, and every result links to the page with the same numbers.

Calculators that work in every country take country (US, UK, CA, AU, IE, NZ or AE) and answer in that currency. Amounts accept shorthand like 50k. Bad inputs return 422 with a message for each field.

curl "https://goodcalcs.com/api/v1/uk-take-home-pay?salary=50000&region=scotland"

{
  "calculator": "uk-take-home-pay",
  "country": "UK",
  "currency": "GBP",
  "inputs": {
    "salary": 50000,
    "…": "…"
  },
  "result": {
    "label": "Take-home pay",
    "value": "£3,293.30 /month",
    "summary": "On £50,000 you take home £3,293 a month.",
    "breakdown": [
      {
        "label": "Salary",
        "value": "£4,166.67"
      },
      {
        "label": "Income tax",
        "value": "−£623.83"
      }
    ],
    "…": "…"
  },
  "page": "https://goodcalcs.com/uk/take-home-pay-calculator/?salary=50000"
}

MCP server for AI assistants

Connect an assistant that supports the Model Context Protocol to https://goodcalcs.com/mcp (Streamable HTTP, no sign-in). It gets three tools: list_calculators, get_calculator and calculate.

In Claude, add it as a custom connector with that URL. In Claude Code:

claude mcp add --transport http goodcalcs https://goodcalcs.com/mcp

Calculators

Terms

Free for reasonable use. Please show results as estimates, link to the calculator page each result gives you, and cache answers rather than calling for every page view. Results are not financial advice. Heavy or commercial use: email us.