Calculate API

Every calculator, one JSON endpoint

The Online Calculator 24 exposes every one of its 3,602 live engines over plain HTTPS. No API key, no signup — send a slug and its inputs, get the result, secondary outputs and worked steps back as JSON. It runs the exact engine the on-site calculator uses.

No keyCORS openGET only60 req / min

Quick start

A slug is the last segment of any calculator URL (…/<slug>), or browse /llms.txt for the structured index. Omitted inputs fall back to the calculator’s own defaults.

cURL

curl "https://tools.calculators24.com/api/calculate?slug=mortgage-calculator&price=500000&down=100000&rate=5.5&term=15"

JavaScript (fetch)

fetch('https://tools.calculators24.com/api/calculate?slug=mortgage-calculator&price=500000&down=100000&rate=5.5&term=15')
  .then(r => r.json())
  .then(d => console.log(d.result));

Python (requests)

import requests
r = requests.get('https://…/api/calculate',
        params={'slug': 'mortgage-calculator', 'price': 500000, 'down': 100000, 'rate': 5.5, 'term': 15})
print(r.json()['result'])

Endpoint

Method	Path	Description
GET	`/api/calculate`	Compute a calculator and return its result as JSON.

Request parameters

Field	Type	Required	Description
`slug`	string	required	The calculator slug. Unknown or hidden slugs return `404`.
`<input>`	number / string	optional	One key per engine field, named exactly as the calculator names it. Numeric & currency fields are coerced to numbers; select/text pass through.
`_unit`	`i` \| `m`	optional	Imperial or metric, for engines that support both.
`_cur`	`USD` \| `GBP` \| `EUR`	optional	Display currency for money-formatted outputs.

Response object

Key	Type	Description
`slug`, `name`, `url`	string	Identity of the engine and its canonical page URL.
`primary`	object	Headline result: `{ label, value, fmt, unit, sub }`.
`result`	number \| null	Shorthand for `primary.value`.
`outputs`	array	Secondary figures, each `{ label, value, fmt, unit }`.
`steps`	array	The worked calculation, step by step (HTML-safe strings).
`error`	string \| null	Engine-level message when inputs are out of range.
`inputs`	object	Echo of the resolved values the engine received.

200 · application/json

{
  "slug": "mortgage-calculator",
  "name": "Mortgage Calculator",
  "url": "https://…/finance-banking/loans-mortgages/mortgage-calculator",
  "primary": { "label": "Total Monthly Payment (PITI)", "value": 3461.24, "fmt": "money2" },
  "result": 3461.24,
  "outputs": [ { "label": "Total Interest Paid", "value": 427043.6, "fmt": "money2" } ],
  "steps": [ "Loan amount = 500000 − 100000 = 400000", "…" ],
  "error": null,
  "inputs": { "price": 500000, "down": 100000, "rate": 5.5, "term": "15" }
}

Status codes

Code	Meaning
200	Computed successfully — read `result`, `outputs`, `steps`.
404	Unknown, unbuilt or hidden `slug`.
422	The engine rejected the inputs; `error` explains why.
429	Over the rate limit (60 requests / minute / IP).

Try it live

GEThttps://tools.calculators24.com/api/calculate

Ready

Fill the fields and press “Send request” to call the live endpoint.

Rate limits & terms

60 requests per minute per IP address. Every response carries Access-Control-Allow-Origin: *, so calling from a browser or any server is fine. Results are estimates provided with no warranty and do not replace professional advice. This endpoint is read-only compute — it exposes no admin API and no stored data beyond what each calculator already shows on its page.