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Flexible Dieting Calculator

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

A flexible dieting calculator turns your maintenance calories into daily macro targets you can fill with any foods. A 25-year-old man, 175 cm and 70 kg, training 3–5 days a week, maintains on about 2,594 kcal: 126 g protein, 72 g fat and 360 g carbohydrate, with roughly 36 g of fibre.

About this tool

Flexible dieting, often called IIFYM (if it fits your macros), swaps meal plans for three numbers: grams of protein, fat and carbohydrate per day. Any food counts as long as the daily totals land close to target. This calculator estimates resting energy with the Mifflin-St Jeor equation, multiplies it by an activity factor, then moves the total 20% down for fat loss or 10% up for muscle gain. Protein is set per kilogram of body weight, fat as a share of calories, and carbohydrate takes whatever energy is left. A fibre figure keeps the food choices honest. A donut shows how the calories divide between the three macros. The numbers are population estimates: real maintenance can differ from the equation by 10% or more, so two to three weeks of weigh-ins should guide adjustments.

How to use it

  1. Describe yourself

    Pick metric or US units and your sex, then enter age, height, weight and the activity level that matches a typical week.

  2. Choose a goal

    Lose fat sets calories 20% under maintenance, Maintain keeps them level, and Gain muscle adds 10%.

  3. Tune protein and fat

    Move the protein slider in grams per kilogram and the fat slider as a percent of calories; carbohydrate fills the remainder.

  4. Read the targets

    Use the gram figures as daily totals, check the working lines, and watch the donut for the share of calories from each macro.

Examples

Man, 25, 175 cm, 70 kg, maintenance

Units
Metric (kg, cm)
Sex
Male
Age
25
Height
175
Weight
70
Activity level
Moderate (3–5 days)
Goal
Maintain
Protein per kg of body weight
1.8
Fat share of calories
25

Result Daily calorie target: 2,594
Protein (g/day): 126
Fat (g/day): 72
Carbohydrate (g/day): 360
Fibre (g/day): 36
Maintenance calories: 2,594
Resting energy (BMR): 1,674
Protein / fat / carb share: 19% / 25% / 56%

  1. Weight = 70 kg, height = 175 cm, age = 25
  2. BMR = 10 × 70 + 6.25 × 175 − 5 × 25 + 5 = 1673.8 kcal
  3. Maintenance = 1673.8 × 1.55 (Moderately active) = 2594.3 kcal
  4. Target = 2594.3 × 1 (Maintenance) = 2594.3 kcal
  5. Protein = 1.8 × 70 = 126 g (504 kcal)
  6. Fat = 25% × 2594.3 ÷ 9 = 72.1 g

Maintenance lands near 2,594 kcal. With 126 g protein and a quarter of calories from fat, about 360 g of carbohydrate fills the rest.

Woman, 30, 165 cm, 60 kg, desk job, cutting

Units
Metric (kg, cm)
Sex
Female
Age
30
Height
165
Weight
60
Activity level
Sedentary (desk job)
Goal
Lose fat
Protein per kg of body weight
1.8
Fat share of calories
25

Result Daily calorie target: 1,267
Protein (g/day): 108
Fat (g/day): 35
Carbohydrate (g/day): 130
Fibre (g/day): 18
Maintenance calories: 1,584
Resting energy (BMR): 1,320
Protein / fat / carb share: 34% / 25% / 41%

  1. Weight = 60 kg, height = 165 cm, age = 30
  2. BMR = 10 × 60 + 6.25 × 165 − 5 × 30 − 161 = 1320.3 kcal
  3. Maintenance = 1320.3 × 1.2 (Sedentary) = 1584.3 kcal
  4. Target = 1584.3 × 0.8 (Fat loss (−20%)) = 1267.4 kcal
  5. Protein = 1.8 × 60 = 108 g (432 kcal)
  6. Fat = 25% × 1267.4 ÷ 9 = 35.2 g

A 20% cut from about 1,584 kcal gives 1,267 kcal. Protein stays high at 108 g, leaving roughly 130 g of carbohydrate.

Same man, lean bulk

Units
Metric (kg, cm)
Sex
Male
Age
25
Height
175
Weight
70
Activity level
Moderate (3–5 days)
Goal
Gain muscle
Protein per kg of body weight
1.8
Fat share of calories
25

Result Daily calorie target: 2,854
Protein (g/day): 126
Fat (g/day): 79
Carbohydrate (g/day): 409
Fibre (g/day): 40
Maintenance calories: 2,594
Resting energy (BMR): 1,674
Protein / fat / carb share: 18% / 25% / 57%

  1. Weight = 70 kg, height = 175 cm, age = 25
  2. BMR = 10 × 70 + 6.25 × 175 − 5 × 25 + 5 = 1673.8 kcal
  3. Maintenance = 1673.8 × 1.55 (Moderately active) = 2594.3 kcal
  4. Target = 2594.3 × 1.1 (Lean gain (+10%)) = 2853.7 kcal
  5. Protein = 1.8 × 70 = 126 g (504 kcal)
  6. Fat = 25% × 2853.7 ÷ 9 = 79.3 g

Adding 10% to 2,594 kcal gives about 2,854 kcal, with the extra energy going mostly to carbohydrate.

How it is calculated

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

W
Body weight in kilograms
H
Height in centimetres
A
Age in years
s
+5 for men, −161 for women
AF
Activity factor, 1.2 to 1.9
G
Goal factor: 0.8 cut, 1.0 maintain, 1.1 gain
P
Protein in grams per kilogram
F
Fat share of calories as a fraction

Resting energy comes from the Mifflin-St Jeor equation, which predicted measured resting metabolism more closely than older equations in its 1990 validation. The activity factor scales it to total daily energy. Protein is priced at 4 kcal per gram, fat at 9 and carbohydrate at 4 (Atwater factors). Fibre is set at 14 g per 1,000 kcal, the adequate-intake ratio used in US dietary guidance. Targets for women are not set below 1,200 kcal or for men below 1,500 kcal.

Sources

When not to use it

  • During pregnancy or breastfeeding, when energy and protein needs rise beyond these equations.
  • With kidney disease or another condition where protein intake is medically limited.
  • For anyone under 18, whose growth needs differ from adult equations.
  • Alongside a history of disordered eating, where tracking numbers can do harm.

Common mistakes

  • Choosing a higher activity level than a typical week supports, which inflates every target.
  • Treating the gram figures as exact rather than a range of about 5 g either way.
  • Filling the carbohydrate budget with low-fibre foods and ignoring the fibre line.
  • Changing targets after a few days instead of averaging two to three weeks of weigh-ins.

Frequently asked questions

What does IIFYM mean?

It stands for 'if it fits your macros'. The idea is that body composition depends mostly on total calories and protein over time, so no food is forbidden as long as the daily protein, fat and carbohydrate totals land near target. Most people following it still build meals around whole foods and leave 10–20% of calories for anything they like.

How much protein suits flexible dieting?

The recommended dietary allowance is 0.8 g per kilogram, a minimum for preventing deficiency. People cutting or lifting weights commonly use 1.6–2.2 g/kg to protect muscle. The slider defaults to 1.8 g/kg and runs from 0.8 to 3.

Why is fat set as a percentage while protein is per kilogram?

Protein needs track lean mass, so body weight is the better anchor. Fat supports hormones and the absorption of fat-soluble vitamins, and US dietary guidance places it at 20–35% of energy for adults, so a share of calories fits it better. Carbohydrate is then whatever energy remains.

Why is the fat-loss target 20% below maintenance?

A proportional cut scales with body size. For most adults 20% works out to roughly 400–700 kcal a day, which tends to produce about 0.5–1% of body weight lost per week. If the result would fall under 1,200 kcal for women or 1,500 kcal for men, the target is held at that floor and a warning appears.

Do I need to hit every macro exactly?

No. Landing within about 5–10 g of protein and carbohydrate and 5 g of fat on most days is enough. Weekly averages matter more than any single day, and protein is the number most worth hitting consistently.

Where does the fibre figure come from?

US dietary guidance sets adequate fibre intake at 14 g per 1,000 kcal. On 2,000 kcal that is 28 g. It is a practical check that the carbohydrate budget is coming from fruit, vegetables, legumes and whole grains rather than mostly refined foods.

How should I adjust if my weight does not change as expected?

Average your weigh-ins for two to three weeks. If the trend differs from the goal, move calories by about 100–200 kcal a day, usually by changing carbohydrate or fat and leaving protein where it is.

Cite this tool

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APA

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

MLA

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

Chicago

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

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