How this calculator works
This calculator mirrors the exact same equations used inside the NutriCal app. The numbers you see here are the numbers the app uses to plan your meals.
The Mifflin-St Jeor equation
Mifflin-St Jeor is the equation recommended by the American Dietetic Association. It estimates your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — using four inputs:
- Body weight in kilograms
- Height in centimeters
- Age in years
- Sex (male or female)
The equation is: BMR = 10·kg + 6.25·cm − 5·age + 5 (male) / −161 (female). It is accurate to within ±10% for about 80% of adults.
Activity multipliers we use
BMR tells you what you burn lying still. To estimate Total Daily Energy Expenditure (TDEE), we multiply BMR by an activity factor:
- Sedentary (little or no exercise): × 1.2
- Lightly active (light exercise 1–3 days/week): × 1.375
- Moderately active (moderate exercise 3–5 days/week): × 1.55
- Very active (hard exercise 6–7 days/week): × 1.725
- Extremely active (physical job + daily training): × 1.9
Macro split by diet type
Once we know your target calories, we split them into protein, fat, and carbs:
- Protein is set by your goal and activity level — between 0.8 and 2.2 grams per kilogram of body weight.
- Fat is a fixed percentage by diet type (e.g., 70% for keto, 30% for balanced, 20% for low-fat).
- Carbs fill whatever calories remain (4 kcal per gram).
Why we use safe calorie floors
The calculator enforces minimums of 1,200 kcal/day for women and 1,500 kcal/day for men. Going below these thresholds long-term risks nutrient deficiencies, muscle loss, and metabolic slowdown. If your math produces a target below the floor, the calculator extends your timeline instead — never the deficit.
Frequently Asked Questions
How accurate is the Mifflin-St Jeor equation?
Mifflin-St Jeor is the equation recommended by the American Dietetic Association and is accurate to within ±10% for roughly 80% of adults. For most people tracking calories, that is plenty accurate. If you have very high muscle mass or are very lean, consider adjusting by ±10–15%.
What's the difference between BMR and TDEE?
BMR is what your body burns at complete rest. TDEE is BMR multiplied by an activity factor (1.2 sedentary → 1.9 extremely active) to account for daily movement and exercise. TDEE is the number to use for calorie targets.
Should I eat below the safety floor?
The calculator enforces minimums of 1,200 kcal/day for women and 1,500 kcal/day for men. Going below these thresholds long-term risks nutrient deficiencies, muscle loss, and metabolic slowdown. If your math produces a target below the floor, the calculator extends your timeline instead.
How do I calculate macros for weight loss?
After you set weight loss as your goal, the calculator picks a protein multiplier based on your activity level (1.6–2.2 g/kg), sets fat at 30% of calories by default (or your chosen diet percentage), and fills the rest with carbs. Protein is the priority macro — keep it high to preserve muscle in a deficit.
Why are my macros different on a keto diet?
Keto presets fat at 70% of calories, protein at 25%, carbs at 5%. To stay in ketosis, you typically need under ~30 g net carbs per day. The calculator automatically applies this split when you select Keto as your diet type.
Metric vs imperial — does the result change?
No. Internally everything is converted to metric before the math runs. Whether you enter 70 kg or 154 lbs, 175 cm or 5'9", the BMR and TDEE outputs are identical to within rounding.
How fast should I lose weight?
For most adults, 0.5–0.9 kg (1–2 lbs) per week is sustainable. Faster loss often means muscle loss and rebound. The calculator defaults to 0.5 kg/week, which is the conservative end of the recommended range.
What happens after I get my numbers?
Take your target calories and macro split into a meal planning app. NutriCal generates a 7-day meal plan hitting your exact macros in 60 seconds — no spreadsheet required. The buttons above open the App Store or Google Play.
For more on calorie tracking, see our complete calorie tracking guide or our how-to on tracking calories.