2026-09-15 9 min

Macro Calculator by Body Fat

Katch-McArdle macros from lean mass — enter body fat %, get BMR from muscle not total weight, plus TDEE and gram targets.

Calculator

Gender

Units

Age

yrs

Full years

Height

Barefoot standing height

Weight

lbs

Morning scale weight

Activity

Body fat %

DEXA, calipers, or a trending scale

Goal

Protein %

Share of calories from protein

Carbs %

Share of calories from carbs

Fat %

Share of calories from fat

Results update live as you type

Status:Lean 57.3 kg (18% BF)Target 2,492 kcalMaintenance — see cards

Results

Daily Target2,492 kcal

Protein186.9 g

Carbs249.2 g

Fat83.1 g

Lean mass57.3 kg

Katch TDEE plus mission

Recommendations

▸Lean mass 57.3 kg at 18% body fat — Katch BMR 1,607.7 prices muscle, not fat
▸Maintenance target 2,492 kcal = 186.9 g protein (2.67 g/kg), 249.2 g carbs, 83.1 g fat
▸Katch beats Mifflin for lean or muscular builds; without a body-fat number use the standard macro page
▸Confirm with 2-4 weeks of trend; re-measure body fat quarterly, not weekly

Results

Normal

Daily Target

2,492 kcal

Katch TDEE plus mission

Protein

186.9 g

With g/kg context

Carbs

249.2 g

Training fuel

Fat

83.1 g

At 9 kcal/g

Lean mass

57.3 kg

Katch engine room

Katch-McArdle from lean mass with standard activity factors; best when body fat is actually measured.

Visualizations

Macro grams

186.9Protein

249.2Carbs

83.1Fat

Calorie share

Protein cal30%

Carb cal40%

Fat cal30%

Target vs range

2,492kcal

1,2004,500

Formula

Rest priced from muscle, scaled to the day, split into grams.

BMR = 370 + 21.6 x lean kg; TDEE = BMR x factor

Alternative Form

Lean = weight x (1 - BF%); grams by 4/4/9

Variables

Symbol	Name	Unit	Description
Lean	Lean mass	kg	Weight minus fat
BMR	Katch rest	kcal/day	370 + 21.6 x lean
TDEE	Maintenance	kcal/day	Katch scaled by activity
Grams	Macro targets	g/day	Split shares by density

Explanation

Fat-free mass drives burn; pricing it directly beats total-weight equations for lean builds.

Derivation

Lean from BF%, Katch-McArdle for BMR, standard multipliers, mission adjust, density split.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Split weight into fat and lean.

Lean = weight x (1 - BF%)

Lean:57.3 kg at 18%

Intermediate: Muscle is the engine

Result: Lean mass known

Step 2

Price rest from lean mass (Katch-McArdle).

BMR = 370 + 21.6 x lean kg

Resting:1,608 kcal

Intermediate: Fat barely burns

Result: Katch BMR set

Step 3

Scale to the full day.

TDEE = BMR x activity

Maintenance:2,492 kcal

Intermediate: Moderate x1.55

Result: Maintenance priced

Step 4

Apply the mission.

Target = TDEE +/- mission

Target:2,492 kcal

Intermediate: Maintenance

Result: Target set

Step 5

Split into grams.

Protein, carbs /4; fat /9

Grams:186.9 / 249.2 / 83.1 g

Intermediate: Normalized shares

Result: Grams set

Step 6

Validate by trend.

Re-measure BF quarterly

Rule:trend decides

Intermediate: Katch beats Mifflin for lean or muscular builds; without a body-fat number use the standard macro page

Result: Lean mass 57.3 kg at 18% body fat — Katch BMR 1,607.7 prices muscle, not fat

Final Answer

2,492 kcal

Worked Examples

See how the calculator works with different scenarios.

Scenario

70 kg at 18% body fat, moderate activity, maintenance.

Inputs

Stats:70 kg / 18% BF

Activity:Moderate

Calculation

Lean = 57.4 kg. Katch BMR = 370+21.6x57.4 = 1,609.8. TDEE = 2,495. At 30/40/30 = 187 / 250 / 83 g.

Result

~2,495 kcal: 187 g protein (2.7 g/kg total, 3.3 lean)

Interpretation

Katch slightly beats Mifflin here because leanness is confirmed.

Understanding Your Result

Your Result: Daily Target: 2,492 kcal

Typical range: Protein 1.6-2.2 g/kg; AMDR 10-35 / 45-65 / 20-35; deficits 250-750/day; surpluses 150-400/day; maintenance validates by flat 2-4 week trend.

What This Means

Katch-McArdle macros from lean mass — enter body fat %, get BMR from muscle not total weight, plus TDEE and gram targets.

Why It Matters

Rest priced from muscle, scaled to the day, split into grams.

Professional Interpretation

Grow movement before cutting food and keep protein plus lifting under any mission — components decide composition, totals decide the scale.

Totals validate, splits guide

The headline total confirms by scale trend; the split chooses training quality and fullness.

Floors are real

Eating below resting burn for long costs muscle, hormones, and adherence.

Recommendations

•Confirm any number with 2-4 weeks of trend
•Protein 1.6-2.2 g/kg with lifting under every goal
•Re-run per 10-15 lbs or training-block change
•Steps before cuts; fuel before assuming surplus failed
•One mission at a time — cut, hold, or gain in phases

Educational Content

Introduction

Katch-McArdle macros from lean mass — enter body fat %, get BMR from muscle not total weight, plus TDEE and gram targets.

Concept Explanation

Pin maintenance from your stats, apply the phase mission, then split the target into protein, carb, and fat grams by energy density.

Applications

▸Setting phase calories before choosing foods

▸Converting one calorie target into shoppable gram goals

▸Comparing cuts, holds, and gains on equal math

▸Fueling training blocks without guesswork

▸Re-estimating needs as body size changes

▸Explaining stalls with numbers not guilt

Benefits

•One headline intake with weekly equivalents
•Gram targets for all three macros
•Per-meal portions built in
•Reference-band checks on protein and fiber
•Trend-first validation guidance

Limitations

•Estimates within ~10-15%, not lab measures
•Single-day snapshot; training and rest days differ
•Activity rungs average diverse lives
•Water and glycogen mask fat pace for 2-3 weeks

Best Practices

•Weigh mornings before food for repeatable inputs
•Log honestly 2-4 weeks before judging
•Hit protein first, then fill carbs and fat
•Lift 2-4x weekly under every goal
•Re-run per 10-15 lbs of change

Common Misconceptions

Myth: The split matters more than the total.

Truth: Calories decide the scale; protein decides composition; the remaining split tunes training and fullness.

Myth: Exercise calories should be eaten back.

Truth: Activity is already inside TDEE here. Eating it back double-counts and erases the mission.

Myth: Faster always finishes sooner.

Truth: Oversized deficits stall via burnout and muscle loss; right-sized finishes first.

Practical Tips

•Validate every estimate with 2-4 weeks of trend
•Hold protein 1.6-2.2 g/kg with 2-4 lifts weekly
•Add steps before cutting food deeper
•Re-run per 10-15 lbs of change
•Keep one mission per phase
•Sleep 7+ hours; short sleep masks fat loss

Common Mistakes

Using goal weight instead of current weight

Equations describe the body burning now. Current weight sets today burn; re-run as you change.

Picking too-high activity

Choose the lower rung when between levels. Overestimated burn is the top cause of stalled progress.

Judging by daily scale noise

Use 7-14 day averages. Water swings kilograms; fat pace reveals over weeks.

Changing splits weekly

Hold one split 3-4 weeks. Constant redesign hides whether anything worked.

Ignoring fiber while chasing macros

Anchor 14 g fiber per 1,000 kcal first, then fit remaining carbs around it.

Assumptions

This calculator makes the following assumptions to provide estimates:

Mifflin rest: BMR from Mifflin-St Jeor with metric internals.

Standard multipliers: Activity factors 1.2 through 1.9 for the five rungs.

Energy densities: Protein and carbs 4 kcal/g; fat 9 kcal/g.

Rounded ledger: Whole-gram outputs summing near the headline total.

Limitations

Be aware of these limitations when using this calculator:

Estimated, not measured: Only the trend validates; treat splits as directions.

Rung coarseness: Five factors average diverse weeks.

No medical tailoring: Pregnancy, teens, and clinical cases need professional guidance.

Snapshot day: Training and rest days differ in reality.

Frequently Asked Questions

Answers to common questions about this calculator.

Why use body fat instead of weight?

Fat burns little; lean mass drives BMR. Katch-McArdle beats Mifflin for lean or muscular builds.

How do I estimate body fat?

DEXA or 7-site calipers rank best; smart scales trend okay. Within ~2–3% is plenty for macro math.

No body fat number?

Use Mifflin-St Jeor (the standard macro page). Katch only wins when body fat is actually known.

What are macronutrients?

Protein, carbohydrate, and fat — the nutrients you need in large amounts. Protein and carbs yield 4 kcal/g; fat yields 9 kcal/g.

How are macro grams calculated from calories?

Grams = calories × share ÷ energy density: protein and carbs ÷ 4, fat ÷ 9. A 2,000 kcal day at 30/40/30 gives 150 g protein, 200 g carbs, 67 g fat.

What is a good starting macro split?

30% protein, 40% carbs, 30% fat suits most active adults. Raise protein when dieting, raise carbs when training hard.

How much protein do active adults need?

1.6–2.2 g per kg daily with training; 1.2–1.6 g/kg for general activity; 0.8 g/kg is the RDA minimum.

When should I recalculate macros?

Per 10–15 lbs of weight change, each training-block change, or when progress stalls 3+ weeks with honest tracking.

Do I need to eat back exercise calories?

No — activity is already inside maintenance via the activity factor. Eating them back double-counts.

How accurate are these nutrition estimates?

Within about 10–15% when stats and activity are honest. Validate against 2–4 weeks of trend: stable weight confirms maintenance, steady drift corrects it.

Should I use current or goal weight?

Current weight. Equations describe the body you have. Re-run per 10–15 lbs of change as needs fall with size.

What activity level should I pick?

Price your real week: desk job with 3 lifts is light-moderate, not heavy. When between rungs, pick the lower one and let the scale confirm.

Do I need to hit macros exactly every day?

No. Weekly averages decide outcomes. Land within ~5–10 g of protein and ~10–15 g of carbs and fat most days.

Should macros differ on rest days?

Optional. Identical daily targets work well; a common refinement trims carbs on rest days while holding protein and fat.

Related Calculators

Explore more calculators related to this topic.

Related Guides

Deepen your understanding with these educational resources.

Protein and Strength While Dieting

Keep the engine while shrinking the chassis.

Setting Calories for Fat Loss

From maintenance to deficit without muscle loss.

Fueling Muscle Gain

Small surpluses plus protein and lifting.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Macronutrient: Protein, carbohydrate, or fat — nutrients needed in gram amounts for energy and structure.
TDEE: Total Daily Energy Expenditure: BMR plus digestion, daily movement, and training.
BMR: Basal Metabolic Rate: calories burned at complete rest for vital functions.
AMDR: Acceptable Macronutrient Distribution Range: 10–35% protein, 45–65% carbs, 20–35% fat.
Thermic effect: Digestion cost: ~20–30% for protein, 5–10% for carbs, 0–3% for fat.
Lean mass: Body weight minus fat — muscle, bone, water, and organs; the main driver of BMR.
Energy balance: Intake minus expenditure: negative loses, positive gains, zero maintains.
Refeed: Planned higher-intake days used to relieve diet fatigue during long cuts.

Authoritative References

Trusted sources and standards referenced by this calculator.

U.S. Dietary Guidelines for Americans Harvard Nutrition Source — Macronutrients WHO — Healthy diet fact sheet NIH Office of Dietary Supplements Academy of Nutrition and Dietetics CDC — Nutrition resources

Applicable Standards

Mifflin-St Jeor (AJCN 1990)U.S. Dietary Guidelines AMDR bandsFAO/WHO/UNU human energy requirements

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Page Information

Last Updated:

2026-09-15

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.