IIFYM Calculator — If It Fits Your Macros
Get your personalised IIFYM macro targets: BMR and TDEE from Mifflin-St Jeor, adjusted for your goal, then split into protein, fat, and carbohydrate grams that fit your calorie budget.
Sex
years
kg
cm
Activity level
Goal
g/kg
% of calories
Your TDEE adjusted for your goal — macros below fit within this total
2,649
kcal/dayProtein
20.4%
Fat
25%
Carbohydrates
54.6%
- 1
BMR (Mifflin-St Jeor)
10 × 75 + 6.25 × 175 − 5 × 28 + 5 = 1,709Calories burned completely at rest — the minimum energy to sustain life. - 2
TDEE (activity multiplier)
1,709 × 1.55 = 2,649 - 3
Daily calorie target
2,649 (no goal adjustment) = 2,649
How does this calculator work?
IIFYM: calculate TDEE (BMR × activity, using Mifflin-St Jeor), adjust for goal, then allocate protein first (default 1.8 g per kg body weight × 4 kcal/g), fat next (default 25% of target × 1/9 kcal/g), and fill the rest with carbs (÷4). Any food is permitted as long as daily macro grams fit the budget.
Formula
How this is calculated
IIFYM ("If It Fits Your Macros") is a flexible dieting framework that focuses on hitting daily macronutrient targets rather than eating specific foods. Any food is permitted as long as the protein, fat, and carbohydrate grams for the day fit within the calorie budget — hence the name.
The calculator starts by estimating your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation (2025 figures used: men BMR = 10 × kg + 6.25 × cm − 5 × age + 5; women BMR = 10 × kg + 6.25 × cm − 5 × age − 161). The BMR is multiplied by an activity factor (1.2–1.9) to give your Total Daily Energy Expenditure (TDEE). Your goal adjustment then moves the target above or below TDEE: −500 kcal for a standard cut (~0.5 kg/week loss), or +500 for a gaining phase.
Macros are then allocated in order of priority: protein is set by body weight (1.6–2.2 g/kg is evidence-based for muscle retention in training; 1.8 g/kg is a common IIFYM default); fat is set as a percentage of target calories (25–35% is a common healthy range, with 25% used here as the default); and the remainder goes to carbohydrates. The Atwater factors convert grams to calories: 4 kcal/g for protein and carbs, 9 kcal/g for fat. These are editable estimates — adjust them to match your preferences and then track real foods against the targets.
Frequently asked questions
A standard macro calculator typically uses a fixed ratio (e.g. 40/30/30 carb/protein/fat) regardless of body weight. IIFYM sets protein first from body weight (supporting muscle), then fat from a percentage of calories, and fills remaining calories with carbs — giving more protein to heavier or more active people automatically.
In principle yes — the framework is food-agnostic. In practice, nutritionists recommend filling most of your targets with minimally processed whole foods to meet fibre, vitamin, and mineral needs, and reserving a small flexible allowance for treats. Hitting macros while eating only junk food is possible but nutritionally suboptimal.
If the protein calories plus fat calories exceed the target calorie total, there are no remaining calories for carbs. This happens when you set a high protein ratio, a high fat percentage, and a large calorie deficit simultaneously. Reduce the fat percentage or protein ratio, or increase the calorie goal, and the carbs will reappear.
Also known as
TG we-Calculate Editorial Team. (2026). IIFYM Calculator — If It Fits Your Macros [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/iifym-calculator
TG we-Calculate Editorial Team. "IIFYM Calculator — If It Fits Your Macros." TG we-Calculate. 2026. https://we-calculate.com/calculator/iifym-calculator.
TG we-Calculate Editorial Team, "IIFYM Calculator — If It Fits Your Macros," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/iifym-calculator
@misc{wecalculate_iifym_calculator, title = {IIFYM Calculator — If It Fits Your Macros}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/iifym-calculator}}, year = {2026}, note = {TG we-Calculate} }
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