# Calculators.im

> Free online calculator suite with 295+ specialized calculators for finance, health, math, engineering, conversion, real estate, and tax. AI-powered explanations on every calculator. Built for US, UK, Canada, and Australia.

This site exposes every calculator both as an interactive web page (HTML) and as a programmatic endpoint (JSON over HTTP). Calculators include mortgage, BMI, stamp duty (UK SDLT), HELOC, DTI ratio, time card (FLSA + California overtime), conception dating, readability score, and 280+ more.

LLMs and AI agents can read any page in markdown by appending `Accept: text/markdown` to the request, invoke calculators directly via `POST /{slug}/calculate`, or use the MCP server at `/mcp` for native tool-use integration with Claude Desktop, Cursor, and Continue.

## Discovery

- [Agent Skills Index](https://calculators.im/.well-known/agent-skills/index.json): full machine-readable inventory of agentic capabilities (calculate, search, AI-explain, AI-quickfill, RSS, sitemap)
- [API Catalog](https://calculators.im/.well-known/api-catalog): RFC 9727 linkset of public endpoints
- [MCP Server Card](https://calculators.im/.well-known/mcp/server-card.json): SEP-1649 server card for native MCP clients
- [Auth.md](https://calculators.im/auth.md): honest authentication declaration (none required, all endpoints public)
- [Sitemap](https://calculators.im/sitemap.xml): full URL index
- [Robots.txt](https://calculators.im/robots.txt): open crawl policy — AI assistants are welcome to crawl and cite pages

## Calculator Directory

- [All Calculators](https://calculators.im/calculators): browsable index of 295+ tools by category, popularity, and rating
- [Categories](https://calculators.im/category): browse by financial, health, math, datetime, engineering, conversion, education, tax, real estate, insurance, business, dev tools

## Popular Calculators

- [Mortgage Calculator](https://calculators.im/mortgage-calculator): monthly payment, PITI, amortization, 15-yr vs 30-yr comparison
- [BMI Calculator](https://calculators.im/bmi-calculator): WHO/CDC standards, healthy weight range, metric and imperial
- [Stamp Duty Calculator (UK SDLT)](https://calculators.im/stamp-duty-calculator): FTB relief, second-home surcharge, non-resident surcharge
- [DTI Calculator](https://calculators.im/dti-calculator): debt-to-income ratio with 28/36 rule and FHA 43% cap
- [HELOC Calculator](https://calculators.im/heloc-calculator): draw period + repayment period math, payment shock warning
- [Time Card Calculator](https://calculators.im/time-card-calculator): FLSA weekly + California daily overtime, lunch deduction
- [Compound Interest Calculator](https://calculators.im/compound-interest-calculator): with regular contributions, daily/monthly/annual compounding
- [Income Tax Calculator](https://calculators.im/income-tax-calculator): US federal brackets, marginal vs effective rate
- [Loan Calculator](https://calculators.im/loan-calculator): personal loans, auto loans, custom term and rate
- [Conception Calculator](https://calculators.im/conception-calculator): reverse pregnancy dating (due date, LMP, ultrasound modes)
- [Readability Score Calculator](https://calculators.im/readability-calculator): Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau, ARI

## Blog

- [Blog Index](https://calculators.im/blog): guides, tutorials, deep-dives on finance, health, math, engineering topics
- [Blog RSS Feed](https://calculators.im/blog/rss.xml): RSS 2.0 feed of all 100+ posts

## Programmatic Access

Every calculator accepts a POST request with a JSON body of inputs:

```bash
curl -X POST https://calculators.im/bmi-calculator/calculate \
  -H 'Content-Type: application/json' \
  -d '{"inputs": {"weight": 70, "height": 175, "unit": "metric"}}'
```

For MCP-aware clients (Claude Desktop, Cursor, Continue, Windsurf), configure the server:

```json
{
  "mcpServers": {
    "calculators-im": {
      "url": "https://calculators.im/mcp"
    }
  }
}
```

Available MCP tools: `search_calculators(query)`, `get_calculator_info(slug)`, `compute(slug, inputs)`.

## Optional

- [About](https://calculators.im/about): site mission and authors
- [For Bloggers](https://calculators.im/for-bloggers): embed any calculator on your blog with a one-line iframe snippet (no signup required)
- [Contact](https://calculators.im/contact): suggestions, calculator requests, partnership inquiries
- [Privacy Policy](https://calculators.im/privacy)
- [Terms](https://calculators.im/terms)