Developers and AI agents

FitCalcs Calculator API

FitCalcs publishes its fitness calculators as a read-only public API and as an MCP server for AI clients. Three GET endpoints return deterministic results that each name the equation behind them: TDEE and calories use the Mifflin-St Jeor equation, BMI uses NHS categories with waist-to-height ratio, and race prediction uses the Riegel model. There is no authentication and no personal data is collected. Released under CC BY 4.0. Informational only, not medical or dietary advice.

REST endpoints

Base URL https://fitcalcs.co.uk/api. All responses are JSON with open CORS, an ETag and edge caching. Full machine-readable contract: OpenAPI 3.1 spec.

MCP server

The same maths is exposed as a remote Model Context Protocol server over streamable HTTP, so MCP-capable AI clients can call the calculators directly.

• Endpoint: https://fitcalcs.co.uk/mcp (JSON-RPC 2.0, POST)
• Manifest: /.well-known/mcp.json
• Tools: calculate_tdee, calculate_bmi, predict_race_times

Equations

• TDEE and calories: Mifflin-St Jeor BMR multiplied by an activity factor of 1.2 to 1.9; weight-change targets at roughly 7,700 kcal per kg.
• BMI: weight kg divided by height m squared, with NHS categories; waist-to-height ratio flags 0.5 and above as increased risk.
• Race prediction: Riegel, T2 = T1 multiplied by (D2 divided by D1) to the power 1.06.

Terms

Read-only and free under CC BY 4.0: attribute FitCalcs and link back to the relevant calculator or the UK fitness statistics page. These tools provide general information, not medical, dietary or training advice. Please cache responses and avoid abusive request rates.