# Fitness and Body Calculators

BMI, ideal weight, calorie needs, macros, one-rep max, heart-rate zones, race pace and prediction, body fat, calorie burn, due date.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://fitness-calc.x402tookit.com/openapi.json
- x402 manifest: https://fitness-calc.x402tookit.com/.well-known/x402
- Catalog (free): https://fitness-calc.x402tookit.com/catalog
- Health (free): https://fitness-calc.x402tookit.com/health
- Uptime (free): https://fitness-calc.x402tookit.com/uptime

## Endpoints (10)

### GET /bmi — $0.02
Body mass index from weight and height, metric or imperial, with the WHO adult category and the 18.5 to 24.9 weight range.
Params: units?: string, weight: number, height?: number, heightFt?: number, heightIn?: number, age?: number
Example: https://fitness-calc.x402tookit.com/bmi?weight=70&height=175

### GET /bmr-tdee — $0.02
Basal metabolic rate (Mifflin-St Jeor), daily calories by activity level, and a calorie target for a weekly weight change.
Params: units?: string, weight: number, height?: number, heightFt?: number, heightIn?: number, sex: string, age: number, activity?: string, weeklyChange?: number
Example: https://fitness-calc.x402tookit.com/bmr-tdee?weight=80&height=180&sex=male&age=30&activity=moderate&weeklyChange=-0.5

### GET /body-fat-navy — $0.02
Body fat percentage estimate from tape measurements (US Navy method) with fat mass, lean mass and a general category.
Params: sex: string, units?: string, height: number, neck: number, waist: number, hip?: number, weight?: number
Example: https://fitness-calc.x402tookit.com/body-fat-navy?sex=male&units=imperial&height=70&neck=15&waist=34

### GET /calorie-burn — $0.02
Calories burned by an activity (walking, running, cycling, swimming and more) from MET values, body weight and duration.
Params: activity: string, weight: number, minutes: number, units?: string
Example: https://fitness-calc.x402tookit.com/calorie-burn?activity=running-6mph&weight=70&minutes=30

### GET /due-date — $0.02
Estimated due date, gestational age and trimester from the last period (Naegele rule), with key milestone dates.
Params: lmp: string, cycleDays?: integer, asOf?: string
Example: https://fitness-calc.x402tookit.com/due-date?lmp=2026-01-01&asOf=2026-03-12

### GET /heart-rate-zones — $0.02
Estimated maximum heart rate (Tanaka, Fox) and five training zones as percent of max or by heart-rate reserve (Karvonen).
Params: age: number, restingHr?: number, maxHr?: number
Example: https://fitness-calc.x402tookit.com/heart-rate-zones?age=40&restingHr=60

### GET /ideal-weight — $0.02
Ideal body weight by the Devine, Robinson, Miller and Hamwi formulas from height and sex, in kg and pounds.
Params: sex: string, units?: string, height?: number, heightIn?: number
Example: https://fitness-calc.x402tookit.com/ideal-weight?sex=male&height=177.8

### GET /macro-split — $0.02
Protein, carbohydrate and fat grams for a calorie target from a preset or your own percentage split.
Params: calories: number, preset?: string, proteinPct?: number, carbPct?: number, fatPct?: number
Example: https://fitness-calc.x402tookit.com/macro-split?calories=2000&preset=balanced

### GET /one-rep-max — $0.02
Estimated one-rep max from weight and reps by the Epley, Brzycki, Lombardi and O'Conner formulas, with a percentage table.
Params: weight: number, reps: integer
Example: https://fitness-calc.x402tookit.com/one-rep-max?weight=100&reps=5

### GET /pace-race — $0.02
Running pace per km and per mile, speed, and predicted times for other race distances using the Riegel formula.
Params: distance: string, time: string
Example: https://fitness-calc.x402tookit.com/pace-race?distance=5k&time=25%3A00

## Terms

Results are computed locally from published formulas and population averages, provided as is, for general information only. They are estimates for healthy adults and can be wrong for an individual (muscle mass, age, pregnancy, medical conditions, medications). This is not medical advice, a diagnosis or a treatment plan: talk to a doctor or registered dietitian before changing diet, exercise or weight, and for anything involving pregnancy, eating disorders, children or illness.