Free Calculation API for Developers

Every calculation engine behind TG we-Calculate is available as a free JSON API: no API key, no signup, CORS enabled from any origin, and a generous free tier of 120 requests per minute per endpoint. Ideal for spreadsheets, scripts, bots, teaching, and prototypes.

Base URL: https://we-calculate.com/api/v1 — the base endpoint itself returns a machine-readable index of all routes.

Quick start

curl "https://we-calculate.com/api/v1/loan-payment?amount=200000&rate=4.5&months=360"
{"amount":200000.0,"annualRate":4.5,"months":360,
 "monthlyPayment":1013.37,"totalPaid":364813.42,"totalInterest":164813.42}

Endpoints

Endpoint	Example	Returns
`GET /api/v1/percentage`	`?value=25&of=200`	X% of Y
`GET /api/v1/percent-change`	`?from=80&to=120`	Percentage change between two values
`GET /api/v1/vat`	`?amount=100&rate=20&mode=add`	Add or remove VAT (mode=add\|remove)
`GET /api/v1/compound-interest`	`?principal=1000&rate=5&years=10&compounds=12`	Compound growth
`GET /api/v1/loan-payment`	`?amount=200000&rate=4.5&months=360`	Annuity payment, total interest
`GET /api/v1/bmi`	`?weight=70&height=175`	BMI + WHO category (kg, cm)
`GET /api/v1/stats`	`?values=1,2,3,4`	Mean, median, stdev, min, max, sum
`GET /api/v1/date-diff`	`?from=2026-01-01&to=2026-12-31`	Days/weeks/months/years between dates
`GET /api/v1/business-days`	`?from=2026-01-01&to=2026-01-31`	Weekday count between dates
`GET /api/v1/add-business-days`	`?start=2026-01-01&days=10`	Date N business days later
`GET /api/v1/convert/length`	`?value=10&from=km&to=mi`	mm cm m km in ft yd mi
`GET /api/v1/convert/weight`	`?value=70&from=kg&to=lb`	mg g kg t oz lb st
`GET /api/v1/convert/temperature`	`?value=100&from=c&to=f`	Celsius, Fahrenheit, Kelvin
`GET /api/v1/convert/lev-euro`	`?amount=100&from=bgn`	Official fixed rate 1.95583
`GET /api/v1/roman`	`?number=2026`	Roman numerals both directions (or ?numeral=MMXXVI)
`GET /api/v1/minguo`	`?gregorian=2026`	Minguo (ROC) ↔ Gregorian years

Terms

Free for personal and commercial use within the rate limit. No authentication, no tracking of request contents. Responses are stable — we add fields but never remove or rename them within v1. If the API is useful to you, a link back to TG we-Calculate in your project or docs is appreciated (but never required).

Need a higher limit, batch endpoints, or a formula we haven’t exposed yet? Email hello@we-calculate.com — we usually ship small additions within days.