How calorie needs are calculated: the key factors
Your daily calorie requirement is built from two components: your Basal Metabolic Rate (BMR) — the energy your body needs at complete rest just to keep systems running — and an activity multiplier that accounts for how much you move each day.
Step 1 — Estimate your BMR
The most widely used formula is the Mifflin-St Jeor equation, which takes into account your weight, height, age, and biological sex. As a rough illustration of how it works:
- For men (assigned male at birth): (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- For women (assigned female at birth): (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
These are population-level estimates. Individual metabolism varies, so treat the output as a useful starting point rather than a precise prescription.
Step 2 — Apply an activity multiplier
Multiply your BMR by a factor that reflects your typical weekly activity. Common bands used in general nutrition guidance are roughly 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), and 1.725 (very active). The result gives you an approximate TDEE — the calories needed to maintain your current weight.
Step 3 — Adjust for your goal
A moderate calorie deficit (eating somewhat below TDEE) is a common approach for weight loss, while staying at or near TDEE supports maintenance. General nutrition guidance often suggests a deficit of around 300–500 kcal per day as a sustainable range, but what is right for you depends on your health, your medication, and your prescriber's guidance — not a formula alone.
Understanding how many calories you burn each day is just as important as the intake side — see our overview of how to know how many calories you burn for more on that piece of the equation. You might also find it useful to explore how many calories different foods contain and what your calorie target actually means day to day.
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Working out your calorie number is one thing — hitting it consistently when appetite fluctuates on a GLP-1 medicine is another challenge entirely. GLP Trackr's food logging feature makes staying on top of your intake as effortless as possible: snap a photo of a meal and the AI scan estimates calories, protein, and macros instantly, without manual searching or guesswork.
Once you have set a calorie target in the app, every meal you log is counted toward it automatically. The daily check-in gives you a running picture of where you stand, and the targets feature lets you set goals for calories, protein, water, and more — so nothing gets forgotten on days when hunger cues are low.
For a broader view of your numbers, the GLP Trackr calorie calculator hub brings together all the tools to help you determine what you need and track it over time.
GLP Trackr helps you capture this data consistently so you can have informed conversations with your prescriber or dietitian — it is not a substitute for their personalised advice, and any specific calorie target should be agreed with your healthcare team.
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Frequently asked questions.
You estimate your Basal Metabolic Rate (BMR) using a formula based on your weight, height, age, and sex, then multiply by an activity factor to get your Total Daily Energy Expenditure (TDEE). This gives a starting estimate; your prescriber or a dietitian can help personalise it.
BMR (Basal Metabolic Rate) is the calories your body needs at complete rest. TDEE (Total Daily Energy Expenditure) adds in the energy you use through daily movement and exercise. TDEE is the more useful number for setting a calorie goal.
There is no single answer — it depends on your weight, activity level, health status, and your prescriber's guidance. A general approach is to eat at a moderate deficit below your TDEE, but your healthcare professional is best placed to recommend a target suited to you personally.
Calorie calculators provide a population-level estimate based on averages. Individual metabolism varies due to factors like muscle mass, hormones, and health conditions, so treat the result as a useful starting point and adjust based on real-world results and advice from your healthcare team.
GLP Trackr lets you set a daily calorie target, then log meals via AI photo scan, barcode, or search. It automatically totals your intake each day and shows your progress toward your goal, making it easy to stay consistent even when appetite is low.