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How to Calculate Your Calorie Target on a GLP-1

One of the most common questions people ask when starting a GLP-1 medication is: "How many calories should I be eating?" It's a great question — and the answer isn't one-size-fits-all. Eat too many and you won't see results; eat too few and you risk muscle loss, fatigue, nutrient deficiencies, and even hair thinning.

This guide walks you through a simple, proven method to calculate a calorie target that supports safe, sustainable weight loss while on a GLP-1.

Why Your Calorie Target Matters on a GLP-1

GLP-1 medications (like semaglutide and tirzepatide) work primarily by reducing appetite and slowing stomach emptying. This naturally leads to eating fewer calories — which is why they're so effective. But "eating less" isn't the same as "eating the right amount."

Without a target, you risk two extremes:

Too Few Calories	Too Many Calories
Muscle loss	Plateaued weight loss
Fatigue, dizziness	Frustration with results
Hair thinning	Not leveraging the medication
Gallstone risk	—
Nutrient deficiencies	—

A calculated target gives you a roadmap — enough of a deficit to lose fat steadily, while eating enough to protect your muscle, metabolism, and overall health.

Step 1: Calculate Your BMR (Basal Metabolic Rate)

Your BMR is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, and organs functioning.

The most widely used formula is the Mifflin-St Jeor Equation:

For Women:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

For Men:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

Need to convert?

Pounds to kg: divide by 2.2
Inches to cm: multiply by 2.54

Example — A 40-year-old woman, 200 lbs, 5'5" (65 in):

Weight in kg: 200 ÷ 2.2 = 90.9 kg
Height in cm: 65 × 2.54 = 165 cm
BMR = (10 × 90.9) + (6.25 × 165) − (5 × 40) − 161
BMR = 909 + 1031.25 − 200 − 161
BMR ≈ 1,579 calories/day

This means her body burns roughly 1,579 calories/day even if she stayed in bed all day.

Step 2: Calculate Your TDEE (Total Daily Energy Expenditure)

Your TDEE factors in how active you are on top of your BMR. Multiply your BMR by the activity factor that best matches your lifestyle:

Activity Level	Description	Multiplier
Sedentary	Desk job, little to no exercise	BMR × 1.2
Lightly active	Light exercise 1–3 days/week	BMR × 1.375
Moderately active	Exercise 3–5 days/week	BMR × 1.55
Very active	Hard exercise 6–7 days/week	BMR × 1.725
Extra active	Physical job + daily training	BMR × 1.9

Continuing our example — sedentary (× 1.2):

TDEE = 1,579 × 1.2
TDEE ≈ 1,895 calories/day

This is roughly how many calories she needs to maintain her current weight.

Be honest about your activity level. Most people overestimate. If you work a desk job and take one or two short walks a week, "sedentary" or "lightly active" is the right choice.

Step 3: Apply a Calorie Deficit

To lose weight, you need to eat fewer calories than your TDEE. A calorie deficit forces your body to use stored fat for energy.

The general guideline for safe, sustainable weight loss is a deficit of 300–500 calories per day, which typically results in 0.5–1 lb of weight loss per week.

Deficit	Approximate Weight Loss	Best For
250 cal/day	~0.5 lb/week	Very gradual; good for smaller bodies
500 cal/day	~1 lb/week	Standard, sustainable target
750 cal/day	~1.5 lb/week	Short-term, higher-BMI individuals
1,000 cal/day	~2 lb/week	Not recommended without medical supervision

Continuing our example — 500-calorie deficit:

Target = 1,895 − 500
Daily Calorie Target ≈ 1,395 calories/day

Step 4: Apply the Safety Floor

This is the most important — and most overlooked — step. Your calorie target should never drop below a minimum floor, regardless of what the math says. Eating too little is dangerous, especially on a GLP-1 where appetite suppression can make it easy to undereat without realizing it.

Minimum recommended calorie floors:

Group	Minimum Daily Calories
Women	1,200
Men	1,500

If your calculated target falls below this floor, use the floor as your target instead. Losing weight slightly slower is far better than damaging your metabolism, losing muscle, or triggering hair loss.

Example check: Our example woman's target of 1,395 is above the 1,200 floor, so she's good. If her TDEE had been lower and the math produced 1,050, she should target 1,200 instead.

Step 5: Adjust Based on Real Results

Calculators give you a starting estimate, not a guarantee. Your real metabolism may differ by 5–15% from any formula. The key is to track and adjust:

Follow your target for 2 weeks without changing anything else.
Weigh yourself 2–3 times per week, same time of day, and average the results.
Evaluate the trend:

Weekly Trend	What It Means	What to Do
Losing 0.5–2 lb/week	On track	Keep going
Losing more than 2 lb/week	Too aggressive — muscle loss risk	Add 100–200 calories back to your target
Losing less than 0.5 lb/week	Deficit too small	Reduce by 100–200 calories (not below the floor)
Gaining or holding steady	Tracking error or metabolic adaptation	Recheck food logging; reduce by 100–200 cal

GLP-1 note: As you lose weight, your body needs fewer calories. Recalculate your TDEE every 10–15 lbs to keep your target accurate.

Special Considerations on a GLP-1

GLP-1 medications change the calorie equation in a few important ways:

1. Appetite Suppression ≠ Automatic Deficit

Even with reduced hunger, it's possible to maintain or even gain weight if the foods you do eat are calorie-dense (oils, nuts, cheese, sweets). Tracking calories ensures your deficit is real.

2. Prioritize Protein Within Your Target

If your target is 1,400 calories, roughly 25–35% should come from protein (about 90–120g). This protects your muscle mass and hair during weight loss. See our guide to eating on a GLP-1 for practical food lists.

3. Don't Chase the Lowest Number

Because GLP-1s make low-calorie eating easier, there's a temptation to restrict aggressively. Resist this. Rapid weight loss increases the risk of:

Muscle loss (including heart muscle in extreme cases)
Gallstones
Hair thinning (telogen effluvium)
Loose/excess skin
Weight regain after stopping the medication

4. Hydration and Calories

GLP-1s can mask thirst the same way they mask hunger. Aim for at least 64–80 oz of water per day. Note that liquid calories (juice, soda, alcohol) add up fast and provide little satiety — minimize them.

Quick Reference: The Full Calculation

Here's the entire method in one place:

Calculate BMR using the Mifflin-St Jeor equation
Multiply by activity factor to get TDEE
Subtract 300–500 calories for a sustainable deficit
Check the floor — never go below 1,200 (women) or 1,500 (men)
Track for 2 weeks, then adjust up or down by 100–200 calories based on results
Recalculate every 10–15 lbs of weight lost

Key Takeaways

Your calorie target = TDEE minus a moderate deficit (300–500 cal).
Never drop below 1,200 (women) or 1,500 (men) without medical supervision.
GLP-1s make eating less easier, but not eating the right amount automatic — you still need a target.
Protein is critical within whatever calorie target you set.
Track, evaluate, and adjust every 2 weeks; recalculate as you lose weight.
Sustainable weight loss is 0.5–2 lbs per week — faster isn't better.

This guide is for educational purposes only and does not constitute medical advice. Calorie targets vary by individual. Always consult your prescribing provider or a registered dietitian before starting a calorie-restricted diet, especially while taking a GLP-1 medication.