Plan a cut

Real questions span several calculators. This walks one person through a cutting plan end to end: estimate body fat, use it to get maintenance calories, then turn a deficit into macros. Meet Sam: male, 32, 180 cm, 85 kg, trains a few times a week (moderate activity), tape measure in hand (neck 40 cm, waist 92 cm).

1. Estimate body fat

import { REGISTRY } from "@almostjacked/fitness-tools";

const bodyFat = REGISTRY.get("body-fat")!;
const bf = bodyFat.compute(bodyFat.input.parse({
  sex: "male", age: 32,
  height: { value: 180, unit: "cm" },
  weight: { value: 85, unit: "kg" },
  neck:   { value: 40,  unit: "cm" },
  waist:  { value: 92,  unit: "cm" },
}));
// bf.results   → navy 19.81 %, deurenberg 22.64 %
// bf.consensus → { mean: 21.225, min: 19.81, max: 22.64, n: 2 }
// bf.skipped   → jackson-pollock-3 (needs skinfold_sum)

Two methods ran and agree within a few points; the skinfold method sat out because Sam has no caliper reading. We’ll carry the consensus, ≈ 21 %, forward.

2. Get maintenance calories

Feeding body_fat into tdee unlocks the lean-mass-based methods (Katch, Cunningham), so all four formulas run:

const tdee = REGISTRY.get("tdee")!;
const t = tdee.compute(tdee.input.parse({
  sex: "male", age: 32,
  height: { value: 180, unit: "cm" },
  weight: { value: 85, unit: "kg" },
  activity: "moderate",
  body_fat: 21.2,
}));
// t.results   → mifflin 2821, harris 2959.4, katch 2816, cunningham 3059 kcal/day
// t.consensus → { mean: 2913.85, median: 2890.2, min: 2816, max: 3059, n: 4 }

Maintenance is roughly 2914 kcal/day (the mean). The ~240 kcal spread between formulas is exactly the kind of uncertainty the consensus makes visible.

3. Turn a deficit into macros

A ~500 kcal/day deficit targets about a pound a week. That’s 2914 − 500 = 2414 kcal. Hand that to macros with a cutting goal (it defaults protein high to protect muscle in a deficit):

const macros = REGISTRY.get("macros")!;
const m = macros.compute(macros.input.parse({
  calories: 2414,
  weight: { value: 85, unit: "kg" },
  goal: "cut",
}));
// m.results[0].detail → { protein_g: 187, fat_g: 76.5, carb_g: 244.4, calories: 2414 }

Sam’s cutting day: 2414 kcal — 187 g protein, 77 g fat, 244 g carbs.

What you just did

You chained three tools, carrying each output into the next as plain data: a body-fat estimate unlocked better TDEE methods, and the TDEE consensus set the calorie budget the macros split. The same chain works over HTTP or from an agent.

Before acting on the numbers, read accuracy & limitations — these are estimates, and the range matters as much as the mean.