About AI Fit Hub

Multi-formula transparency. Our TDEE calculator doesn't give you one number from one formula — it runs Mifflin-St Jeor, Harris-Benedict, WHO/FAO, and optionally Katch-McArdle, then shows the range so you know how confident the estimate is. Same pattern for 1RM (six formulas averaged with the spread visible) and ideal weight (four formulas; we show the range, not a single "target").

Methodology on every page. Every calculator links to a methodology page with the formula, the year it was derived, the population it was derived on, the approximation range, the citation, and a change log. FFMI's 25 "natural ceiling" is an observational claim from Kouri 1995 (n=157), not a biological law — and the methodology page says so.

Goal-based tool router. Answer a few questions at /plan/ and we route you through the calculators that answer your question — TDEE, macros, protein, training split, timeline. It's a tool picker that chains calculators together; it doesn't prescribe what you should do with the output.

Result-aware hedging. Tools explain what your specific output means and where it stops being reliable. Low TDEE? We surface the minimum-calorie floor. 1RM from 15 reps? We flag that the estimate is less reliable than from 5. No extrapolation into ranges the underlying research didn't cover.

Agent-first API. Every tool has a JSON API that ChatGPT, Claude, and custom agents can call directly. The /api/plan/ endpoint chains multiple tools into a single call.

Works at the gym. The site is a PWA — install it on your home screen and use it offline. No signal needed for plate loading, 1RM calculations, or heart rate zones.

AI Fit Hub is built by Christoph (product, strategy) and Rusty (AI co-founder — builds, tests, and deploys continuously). Part of the Orbyd AI Hub Network.

Not sure which tool? Open /plan/ — answer a few questions, get routed through the calculators that match.

Know what you need? Go to All Tools and search.

Want the math? Every tool links to its methodology page with formula, citation, assumptions, and limits.

Want to learn? Browse the guides, comparisons, formulas, and glossary.

Track over time? Save results to your Dashboard — stored locally in your browser.

Building an agent? See AI Integrations for API endpoints and contracts.

Independent and ad-free. No sponsors, no affiliate links, no paid placements. Funding disclosure policy at /sponsor-disclosure/.

Zero tracking. No cookies, no analytics pixels, no PII collection. Body measurements never leave your browser.

Zero signup. Every tool works immediately. No account walls, no email gates, no "sign up to see your results."

Formula transparency. Every calculator shows which formula it uses and links to the peer-reviewed source. We cite PubMed and DOI, not "studies show."

Body-neutral language. Our tools calculate — they don't prescribe. "Energy needs" not "calories to lose weight." We show ranges, not judgments.

Not medical advice. Every page renders an education banner. We help you understand your numbers, not diagnose or treat conditions.