Why this calculator is different

Most macro tools guess. Ours uses Mifflin–St Jeor (validated as the most reliable for resting energy needs in non-athlete populations) and automatically switches to Cunningham/Katch–McArdle when you provide body-fat %, which directly leverages lean mass.   For context: Mifflin–St Jeor outperformed Harris-Benedict and others in accuracy; Cunningham models RMR from fat-free mass (LBM = biggest driver of BMR).

How your macros are calculated (the science in plain English)

Step 1 — Estimate Resting Metabolism (BMR)

• Mifflin–St Jeor when body-fat is unknown. Validated as the most reliable across common equations.
• Cunningham/Katch–McArdle (uses lean mass) when body-fat % is provided.

Step 2 — Adjust for Activity (TDEE)

Your daily energy need = BMR × activity multiplier (sedentary → extra active). This gives maintenance calories (TDEE).

Step 3 — Set a Goal (deficit or surplus)

• Fat loss: a gradual approach is best. Public-health guidance: ~1–2 lb/week is more sustainable. That’s roughly a ~500–1000 kcal/day deficit as a starting estimate. The calculator supports presets (10–20%) or a custom lb/kg per week target.
• Muscle gain: small surpluses (≈5–10%) help minimize fat gain.

Step 4 — Distribute calories into protein, fat, and carbs

• Protein: Research shows benefits up to ~1.6 g/kg/day (≈0.7 g/lb) for strength and hypertrophy; some individuals may benefit from the higher end of 1.6–2.2 g/kg depending on training status and goals. The calculator lets you choose method (per lb BW, per kg BW, or per lb lean mass).
• Fat: We anchor fat to a minimum ~20–35% of calories per AMDR and let you slide within that range.
• Carbs: Fill the remainder (carbs are highly performance-relevant for most training). AMDR for carbs is 45–65% of calories (your exact % depends on protein/fat choices and training demands).
• Fiber target: ~14 g per 1000 kcal (shown in your results) helps with satiety and health.

Example set-ups (quick presets)

• General fat loss lifter:
  
  Protein: 0.8 g/lb BW, Fat: 25% of calories, Carbs = remainder, Goal: ~15% deficit.

• Lean bulk:
  
  Protein: 0.8–1.0 g/lb BW (or 1.0 g/lb LBM if BF% known), Fat: 25–30%, Carbs = remainder, Goal: +5–10% surplus.

• Body recomp (new lifter or returning):
  
  Protein: 0.9–1.0 g/lb BW, Fat: 25%, Carbs remainder, Goal: ~5% deficit.

Tip: If progress stalls ≥2–3 weeks, tweak calories by ~150–250/day and re-check weekly trends—scale, measurements, gym performance, and photos.

FAQ

Is this “exact”?

No equation is perfect for every person. Mifflin–St Jeor tends to be the most reliable starting point; Cunningham can improve accuracy when lean mass is known. Track and adjust.

Why not always use Katch–McArdle/Cunningham?

It requires a reasonable body-fat % estimate; bad inputs → bad outputs. When BF% is unknown, Mifflin–St Jeor is preferred.

How fast should I lose weight?

Most people do best aiming for ~1–2 lb/week. Faster cuts increase muscle loss risk and rebound odds.

Where do your macro ranges come from?

From the AMDR and strength-training protein research (e.g., ~1.6 g/kg/day).

References

• Mifflin MD et al., 1990 — original Mifflin–St Jeor paper.
• Frankenfield D. et al., 2005 — comparative accuracy: Mifflin–St Jeor most reliable vs. common equations.
• Cunningham JJ, 1980 — RMR predicted from lean body mass.
• Institute of Medicine / National Academies — AMDR: carbs 45–65%, fat 20–35%, protein 10–35%.
• Dietary Guidelines/ODPHP Appendix — 14 g fiber per 1000 kcal.
• Morton RW et al., 2018 — protein meta-analysis ~1.6 g/kg/day suffices for most.
• CDC (Jan 17, 2025) — gradual weight loss 1–2 lb/week is more sustainable.