Free finance calculators for every part of life, exposed as a REST API and an MCP server so AI assistants can do the math for you.

Live site: https://everycalc.xyz API docs (OpenAPI): https://everycalc.xyz/api/v1/openapi.json MCP endpoint: POST https://everycalc.xyz/mcp (Streamable HTTP, no auth)

What it is

EveryCalc is a collection of interactive personal-finance calculators. This repo hosts the server code that powers two machine-friendly interfaces on top of those calculators:

REST API at everycalc.xyz/api/v1/* — plain GET endpoints, JSON in and out.
MCP server at POST everycalc.xyz/mcp — eight calculator tools for Model Context Protocol clients (Claude, Cursor, and friends).

No API key. No signup. No local install for the hosted version.

Every tool result includes a calculator_url deep link to the matching interactive calculator on everycalc.xyz, so users can explore the numbers visually after the assistant does the math.

The 8 tools

Tool	What it computes
`calculate_mortgage`	Monthly payment breakdown: principal and interest via the amortization formula, plus property tax, homeowner insurance, PMI, and HOA
`calculate_refinance`	Refinance break-even month and lifetime savings
`calculate_affordability`	Home affordability via the 28/36 rule
`calculate_loan`	Amortizing loan payments
`calculate_compound_interest`	Compound interest projections with monthly contributions
`calculate_percentage`	Percentage calculations
`calculate_tip`	Tip and bill splitting
`calculate_salary`	Salary conversions between hourly, weekly, biweekly, monthly, and annual pay

Use the hosted MCP server

Add this to your MCP client config:

json

{
  "mcpServers": {
    "everycalc": {
      "url": "https://everycalc.xyz/mcp"
    }
  }
}

That is the whole setup. The server is remote (Streamable HTTP), so there is nothing to install.

Use the REST API

All endpoints are GET with query parameters. Example:

GET https://everycalc.xyz/api/v1/calculate/mortgage?home_price=400000&down_payment_pct=20&annual_rate_pct=6.5&term_years=30

Response:

json

{
  "ok": true,
  "tool": "calculate_mortgage",
  "inputs": { "homePrice": 400000, "annualRatePct": 6.5, "termYears": 30, "...": "..." },
  "results": {
    "loan_amount": 320000,
    "down_payment_usd": 80000,
    "monthly_principal_interest": 2022.62,
    "monthly_total": 2022.62,
    "total_interest": 408142.36,
    "total_cost": 808142.36
  },
  "calculator_url": "https://everycalc.xyz/mortgage-calculator/"
}

Available endpoints (full spec in openapi.json):

GET /api/v1/health
GET /api/v1/calculate/mortgage
GET /api/v1/calculate/refinance
GET /api/v1/calculate/affordability
GET /api/v1/calculate/loan
GET /api/v1/calculate/compound-interest
GET /api/v1/calculate/percentage
GET /api/v1/calculate/tip
GET /api/v1/calculate/salary
GET /api/v1/openapi.json

Errors return {"ok": false, "error": {"code": "...", "message": "...", "field": "..."}} with an appropriate HTTP status.

Run it yourself

The server is a Cloudflare Worker. The calculation math lives in src/engine.js as pure functions (no I/O), shared by the REST handlers and the MCP handlers in src/index.js.

Prerequisites: Node 18+, wrangler.

bash

npm install -g wrangler
wrangler login
# point [assets] directory at your static-site build, then:
wrangler deploy

The OpenAPI document is generated from the same handlers, so API docs never drift from behavior.

Tests

bash

npm test

test/test.mjs exercises the REST endpoints against the pure math functions; test/test-mcp.mjs exercises the MCP tool handlers. All green as of the last deploy.

MCP registry

This repo includes server.json, the manifest for the official MCP registry.

License

MIT. See LICENSE.

EveryCalc

What it does

What it costs

Tools

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