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IIFYM Calculator

HealthDiet and Nutrition Planning
About you
Sex
Units
Goal and macros
Goal
Daily calorie target —
Protein (g/day)
—
Fat (g/day)
—
Carbohydrate (g/day)
—
BMR (kcal)
—
Maintenance TDEE (kcal)
—
Where the calories come from
The chart appears with your result

An IIFYM calculator turns body stats into a calorie target and three macro numbers. A 30-year-old man at 80 kg and 180 cm with a desk job burns about 2,136 kcal a day; at 1.6 g/kg protein and 25% fat that is 128 g protein, 59 g fat and roughly 273 g carbohydrate.

About this tool

If It Fits Your Macros is a flexible dieting approach: any food is allowed as long as the day ends near set gram totals for protein, fat and carbohydrate. This page builds those totals. It estimates resting energy use with the Mifflin-St Jeor equation, multiplies by an activity factor, applies a 500 kcal deficit or 300 kcal surplus if you pick one, then fixes protein by body weight, fat as a share of calories and gives carbohydrate whatever energy is left. A donut shows how the calories divide among the three macros, and the working lists every multiplication. The estimate is a starting point: the equation has no term for body composition, so very muscular or very heavy people may sit 10% or more away from the figure, and the target should be adjusted against two to three weeks of scale data.

How to use it

  1. Enter sex, age and size

    Pick metric or US units, then give weight and height. Sex selects the +5 or −161 constant in the equation.

  2. Choose activity and goal

    The activity list sets the multiplier from 1.2 to 1.9; the goal adds −500, 0 or +300 kcal.

  3. Set protein and fat

    Drag the sliders for grams of protein per kg and the fat percentage. Carbohydrate is the remainder.

  4. Read the gram targets

    Check the three gram figures, the donut split and the working below them.

Examples

Man, 30, 80 kg, 180 cm, desk job

Sex
Male
Units
Metric (kg, cm)
Age
30
Weight
80
Height
180
Activity level
Sedentary (×1.2)
Goal
Maintain
Protein per kg of body weight
1.6
Fat share of calories
25

Result Daily calorie target: 2,136
Protein (g/day): 128
Fat (g/day): 59
Carbohydrate (g/day): 273
BMR (kcal): 1,780
Maintenance TDEE (kcal): 2,136

  1. BMR = 10 × 80 kg + 6.25 × 180 cm − 5 × 30 + 5 = 1780 kcal
  2. TDEE = 1780 × 1.2 = 2136 kcal
  3. Target = 2136 + 0 = 2136 kcal
  4. Protein = 1.6 g × 80 kg = 128 g (512 kcal)
  5. Fat = 25% × 2136 ÷ 9 = 59.3 g
  6. Carbs = (2136 − 512 − 534) ÷ 4 = 272.5 g

A resting rate of 1,780 kcal times 1.2 gives 2,136 kcal to maintain. 1.6 g/kg sets protein at 128 g and 25% fat is 59 g; carbohydrate takes the remaining 1,090 kcal.

Woman, 25, 60 kg, training 4 days, cutting

Sex
Female
Units
Metric (kg, cm)
Age
25
Weight
60
Height
165
Activity level
Moderate, 3–5 d (×1.55)
Goal
Lose (−500 kcal)
Protein per kg of body weight
1.6
Fat share of calories
25

Result Daily calorie target: 1,585
Protein (g/day): 96
Fat (g/day): 44
Carbohydrate (g/day): 201
BMR (kcal): 1,345
Maintenance TDEE (kcal): 2,085

  1. BMR = 10 × 60 kg + 6.25 × 165 cm − 5 × 25 − 161 = 1345.3 kcal
  2. TDEE = 1345.3 × 1.55 = 2085.1 kcal
  3. Target = 2085.1 − 500 = 1585.1 kcal
  4. Protein = 1.6 g × 60 kg = 96 g (384 kcal)
  5. Fat = 25% × 1585.1 ÷ 9 = 44 g
  6. Carbs = (1585.1 − 384 − 396.3) ÷ 4 = 201.2 g

Maintenance is 1,345 × 1.55 = 2,085 kcal; a 500 kcal deficit leaves 1,585 kcal split into 96 g protein, 44 g fat and 201 g carbohydrate.

Man, 35, 180 lb, 5 ft 10 in, lean bulk

Sex
Male
Units
US (lb, ft, in)
Age
35
Weight
180
Height
5
and
10
Activity level
Light, 1–3 days (×1.375)
Goal
Gain (+300 kcal)
Protein per kg of body weight
2
Fat share of calories
30

Result Daily calorie target: 2,717
Protein (g/day): 163
Fat (g/day): 91
Carbohydrate (g/day): 312
BMR (kcal): 1,758
Maintenance TDEE (kcal): 2,417

  1. BMR = 10 × 81.6 kg + 6.25 × 177.8 cm − 5 × 35 + 5 = 1757.7 kcal
  2. TDEE = 1757.7 × 1.375 = 2416.9 kcal
  3. Target = 2416.9 + 300 = 2716.9 kcal
  4. Protein = 2 g × 81.6 kg = 163.3 g (653 kcal)
  5. Fat = 30% × 2716.9 ÷ 9 = 90.6 g
  6. Carbs = (2716.9 − 653.2 − 815.1) ÷ 4 = 312.2 g

180 lb is 81.6 kg, so 2.0 g/kg is 163 g of protein. A 300 kcal surplus over a 2,417 kcal maintenance gives 2,717 kcal.

How it is calculated

BMR = 10W + 6.25H − 5A + s; Target = BMR × F + G; Protein g = p × W; Fat g = Target × f ÷ 9; Carb g = (Target − 4 × Protein g − 9 × Fat g) ÷ 4

W
Body weight in kg
H
Height in cm
A
Age in years
s
+5 for men, −161 for women
F
Activity factor, 1.2 to 1.9
G
Goal offset: −500, 0 or +300 kcal
p, f
Protein in g/kg and fat as a fraction of calories

Mifflin-St Jeor was fitted on 498 adults in 1990 and is the resting-energy equation the Academy of Nutrition and Dietetics found most reliable for healthy adults. Multiplying by an activity factor gives total daily energy expenditure. Protein supplies 4 kcal per gram, carbohydrate 4 and fat 9 (Atwater factors). Protein is anchored to body weight because muscle retention depends on grams, not on a percentage; carbohydrate absorbs the remaining energy so the three macros always add up to the target.

Sources

When not to use it

  • During pregnancy or breastfeeding, when energy needs follow different rules.
  • For children and teenagers still growing; the equation was fitted on adults.
  • With kidney disease or diabetes, where protein and carbohydrate limits come from a care team.

Common mistakes

  • Picking a high activity level for a desk job plus three gym sessions, which inflates the target by several hundred kcal.
  • Setting protein from a goal weight far from current weight without noting the change in grams.
  • Treating the gram totals as exact rather than a range of roughly ±5 g to hit each day.
  • Logging raw versus cooked food weights inconsistently, which skews tracked macros.

Frequently asked questions

What does IIFYM stand for?

If It Fits Your Macros. It is a flexible dieting style in which the daily gram totals for protein, fat and carbohydrate matter, and the food choices that reach them are left to you. Fibre and micronutrients still need attention, which is why many people keep most of the day to whole foods.

How much protein per kilogram is reasonable?

The adult RDA is 0.8 g/kg, the minimum to avoid deficiency. Sports nutrition reviews commonly cite 1.6 g/kg as the point where extra protein stops adding muscle gain for most lifters, with 2.0–2.4 g/kg used during aggressive cuts. The slider runs from 0.8 to 3.3 g/kg.

Why is fat set as a percentage?

Dietary fat supports hormone production and absorption of vitamins A, D, E and K. The Dietary Guidelines for Americans give 20–35% of calories as the acceptable range for adults, so tying fat to total energy keeps it in that band as the target moves. Below 20% the page adds a note.

Why is carbohydrate what is left over?

Protein has a body-weight floor and fat has a health floor, while carbohydrate has no essential minimum for adults. Letting carbohydrate absorb the remainder keeps the three macros summing exactly to the calorie target. If protein and fat already exceed the target, the tool reports an error instead of a negative carb number.

How large a deficit does the lose option use?

A flat 500 kcal per day below maintenance, a common default that has traditionally been linked to about 0.5 kg (1 lb) of loss per week. The NIDDK Body Weight Planner shows the real rate slows as weight falls, so recheck the target after each 4–5 kg.

Is the gain surplus enough to build muscle?

A 300 kcal surplus is a lean-bulk setting meant to limit fat gain; trained lifters typically gain muscle slowly, around 0.25–0.5 kg a month, so a larger surplus mostly adds fat. Beginners may grow at a faster rate on the same intake.

What if my weight does not move as predicted?

Equations predict the average; individuals vary by around 10%. Track weight daily for two to three weeks, compare the weekly average with the expected change and shift calories by 100–200 kcal, taking the change from carbohydrate or fat while holding protein steady.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 28). IIFYM Calculator. Tools Directory. Retrieved October 28, 2026, from https://tools.milunir.com/health/diet-and-nutrition-planning/iifym-calculator/

MLA

Tools Directory Editorial Team. “IIFYM Calculator.” Tools Directory, 28 Oct. 2026, https://tools.milunir.com/health/diet-and-nutrition-planning/iifym-calculator/. Accessed 28 Oct. 2026.

Chicago

Tools Directory Editorial Team. “IIFYM Calculator.” Tools Directory. Last modified October 28, 2026. Accessed October 28, 2026. https://tools.milunir.com/health/diet-and-nutrition-planning/iifym-calculator/.

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