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About this tool
Calculate your perfect daily macros for fat loss, muscle gain, or maintenance.
The Macro Calculator turns your age, sex, height and weight into a daily protein, carbohydrate and fat target by estimating BMR with the Mifflin-St Jeor equation, multiplying it by an activity factor from 1.2 to 1.9 to get TDEE, then adjusting by 250 or 500 calories for a cut or a bulk. It converts the resulting calorie target into grams using 4 calories per gram for protein and carbs and 9 per gram for fat, across four preset splits. It is for anyone setting up a food-tracking app and needing starting numbers rather than a guess. The output is general information, not a clinical prescription — talk to a doctor or registered dietitian before changing your intake if you have a medical condition.
Open Macro Calculator on AltFTool — it loads instantly in your browser.
Enter Age, Gender, Weight (kg) and Height (cm), then pick the BMR Formula — Mifflin-St Jeor (Default), Harris-Benedict, or Katch-McArdle, which reveals a Body Fat % field and works from lean body mass.
Choose an Activity Level from Sedentary (Little or no exercise) to Athlete (Twice daily training), which multiplies BMR by 1.2 to 1.9; set a Primary Goal of -500, -250, Maintain Weight, +250 or +500 kcal and a Macro Split of Balanced (30P/40C/30F), High Protein (40P/30C/30F), Low Carb (35P/25C/40F) or High Carb (25P/50C/25F), then click Calculate Macros.
Read BMR, TDEE, Target Calories and Water Intake, then the Daily Macro Targets cards giving protein, carb and fat in grams — calories divided by 4, 4 and 9 — with each macro's percentage of the calorie target.
Switch between Mifflin-St Jeor, Harris-Benedict and Katch-McArdle so you can see how much the choice of formula actually moves your number.
Each split is applied to your calorie target and divided by the Atwater factors, so you get grams to log rather than percentages to work out yourself.
Goals move your TDEE by a defined 250 or 500 calories rather than an opaque percentage, so you can see exactly what changed.
Mifflin-St Jeor by default: 10 x weight in kg plus 6.25 x height in cm minus 5 x age, then plus 5 for men or minus 161 for women. That gives BMR, which is then multiplied by your activity factor to give TDEE.
1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for very active and 1.9 for athlete-level training. Most people who train three to five times a week and are otherwise desk-bound land on 1.55.
This calculator offers a 250-calorie deficit for a slower cut and a 500-calorie deficit for a faster one, with matching 250 and 500 surpluses for bulking. A 500-calorie daily deficit is the conventional starting point for roughly half a kilogram a week, though real results vary with adherence and activity — check with a doctor or dietitian before a large or prolonged deficit.
Each macro's share of your calorie target is divided by its calorie density: 4 calories per gram for protein, 4 for carbohydrate and 9 for fat. The balanced preset is 30 percent protein, 40 carbs and 30 fat; the alternatives are high protein at 40/30/30, low carb at 35/25/40, and high carb at 25/50/25.
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