Protein-to-Calorie Ratio Calculator: GLP-1 Weight Loss Success
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The Calorie Formulas Behind the Calculator (Mifflin-St Jeor)
BMR (Basal Metabolic Rate) is what your body burns at complete rest. Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics validates as most accurate for the general population — within about 10% for most adults.
Multiplying BMR by an activity factor gives TDEE (Total Daily Energy Expenditure) — the maintenance number. A 500 kcal daily deficit produces roughly 0.5 kg (1 lb) of fat loss per week because a kilogram of fat stores about 7,700 kcal.
Worked Example: Woman, 35 y, 70 kg, 165 cm, lightly active
BMR = 10×70 + 6.25×165 − 5×35 − 161 = 700 + 1031.25 − 175 − 161 ≈ 1,395 kcal
TDEE = 1,395 × 1.375 (lightly active) ≈ 1,918 kcal — maintenance
Fat loss target: 1,918 − 500 ≈ 1,418 kcal/day → about 0.5 kg/week
Lean gain target: 1,918 + 250 ≈ 2,168 kcal/day → ~0.25 kg/month gain
Never eat below your BMR for extended periods — the deficit should come between TDEE and intake, not out of your basic metabolic needs. Below ~1,200 kcal (women) or ~1,500 kcal (men), nutrient adequacy gets difficult without medical supervision.
Frequently Asked Questions
Why do calorie calculators disagree?
They use different equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) and activity multipliers. Katch-McArdle uses lean body mass and is better for muscular people. Treat every estimate as a starting point to adjust by weekly weigh-in results.
How accurate is BMR really?
Within ±10% for most healthy adults. Lab measurement (indirect calorimetry) is the gold standard. Genetics, thyroid status, and prior dieting history shift real BMR — so adjust targets based on 2-3 weeks of actual data.
Do I eat back exercise calories?
If you chose an activity factor that already includes workouts (moderately/very active), do not add them again. If you chose sedentary and log exercise separately, eating back ~50-75% of tracker-reported burn avoids double counting — trackers overestimate.
What is the minimum safe calorie intake?
General floors: about 1,200 kcal/day for women and 1,500 kcal/day for men without medical supervision. Below these, meeting protein, vitamin, and mineral needs becomes impractical, and metabolic adaptation accelerates.
Authoritative Sources & Further Reading
Last reviewed: September 2026. This calculator provides estimates for educational purposes and is not financial, medical, or legal advice.
Quick Article Navigation
Losing weight on Wegovy or Ozempic? This page helps you:
- Prevent muscle loss during rapid weight reduction.
- Calculate your exact Protein-to-Calorie ratio.
- Set daily macronutrient targets.
Explain Your Inputs: Why We Need This Data
To calculate your metabolic needs, we require:
- Age, Gender, Height, Weight: Used to calculate your Basal Metabolic Rate (BMR).
- Activity Level: Determines your Total Daily Energy Expenditure (TDEE).
Interpretation Guide: Actionable Context
What do your macro targets mean?
- If your protein is < 20% of calories: You are at high risk for muscle loss on a GLP-1 medication. Increase lean protein intake.
- If your protein is 25-30% of calories: You are in the optimal zone for preserving lean mass while burning fat.
Explainable Logic: The Math Behind the Tool
We use the Mifflin-St Jeor equation to find your BMR, then apply an activity multiplier.
The Formula: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + s (s = +5 for males, -161 for females).
We then calculate protein needs at 1.2g - 1.5g per kg of ideal body weight.
People Also Ask (PAA)
How much protein should I eat on Ozempic? Most experts recommend a minimum of 90 to 100 grams of protein per day while on GLP-1 medications to prevent muscle wasting, though this varies based on your height and weight.
Why am I losing muscle on Wegovy? Rapid weight loss often includes muscle loss if protein intake and resistance training are inadequate. GLP-1s reduce appetite, making it hard to eat enough protein.
Can I build muscle while on GLP-1s? Yes, by maintaining a high protein diet and engaging in consistent resistance training, you can build muscle while losing fat, though it is more challenging in a steep caloric deficit.
Expand Your Health Suite
- BMI Calculator — Track your overall weight category.
- Body Fat Calculator — Ensure you are losing fat, not muscle.
Pro Tip: Thanks to our Calculation Cards feature, your results are saved to your profile history. You can safely navigate to our other guides without losing your context!
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