What the engine actually does
Twelve layers of arithmetic sit between your answers and your target. Here are the six that move it most, and the evidence behind each one.
- 1
Resting metabolism, by Mifflin-St Jeor
We start with the energy your body uses doing nothing at all, calculated from your age, height, weight and sex using the Mifflin-St Jeor equation. It is the equation most dietitians reach for first, and it is where an honest calculation has to begin.
- 2
Activity and total daily burn
That resting figure is scaled by how you actually move: your general activity through the week, and whether your training leans on strength, cardio or a mix of both. The result is your total daily energy expenditure, the number your intake is measured against.
- 3
Adaptive thermogenesis
A lighter body burns less than the same body did when it was heavier, and it burns a little less than the maths alone predicts. The engine accounts for that drift, which is why your numbers should change as you do rather than stay frozen at the figure you were given in month one.
- 4
The dose-aware appetite ceiling
Your medication, your current dose and how long you have been on it together set a realistic upper limit on how much you can eat. When that ceiling falls below your calorie target, the engine says so plainly and switches to protein-priority mode instead of pretending the gap is not there.
- 5
Protein and lean mass protection
Protein is calculated as a floor, from your body weight and your training, before carbs and fat are given any room. Losing weight fast costs muscle when protein is low, and muscle is the part you want to keep.
- 6
The cycle phase layer
Energy needs, appetite and how food feels all move across a cycle, and a flat daily number hides that. The engine adjusts by phase, and if you have no cycle to track, that layer simply steps aside.
The appetite ceiling, by drug and by dose
An appetite ceiling is an estimate of how much food a person is likely to manage in a day at a given dose, expressed as a share of what they would have eaten before the medication. It is not a target and it is not a limit anyone imposes on you. It is a description of what the drug is doing to your hunger, and it matters because once the ceiling drops below your calorie target, chasing the target is the wrong instinct. Protein comes first instead.
These are the exact factors the calculator uses. Only the semaglutide table is anchored to trials that measured energy intake directly. The other four are modelled from what is known about each molecule, and each says so in its own note. A modelled curve is still better than the silence every other calculator offers on this question, but it is not the same thing as a measurement, and you should treat the two differently.
Ozempic, Wegovy
Semaglutide, injected weekly
| Dose | Appetite remaining | Ceiling on a 2,100 kcal day |
|---|---|---|
| 0.25 mg | 88% | about 1,848 kcal |
| 0.5 mg | 82% | about 1,722 kcal |
| 1 mg | 76% | about 1,596 kcal |
| 1.7 mg | 70% | about 1,470 kcal |
| 2.4 mg | 65% | about 1,365 kcal |
Anchored at 1.0 mg and 2.4 mg, where energy intake at an ad libitum meal was measured directly rather than estimated. Doses in between are interpolated.
Mounjaro, Zepbound
Tirzepatide, injected weekly
| Dose | Appetite remaining | Ceiling on a 2,100 kcal day |
|---|---|---|
| 2.5 mg | 85% | about 1,785 kcal |
| 5 mg | 75% | about 1,575 kcal |
| 7.5 mg | 65% | about 1,365 kcal |
| 10 mg | 60% | about 1,260 kcal |
| 12.5 mg | 55% | about 1,155 kcal |
| 15 mg | 50% | about 1,050 kcal |
Modelled, not measured. No published trial has measured ad libitum energy intake across the tirzepatide dose range the way Blundell and Friedrichsen did for semaglutide. Dual agonism suppresses intake harder at the top of the range, which is why 15 mg is modelled near half of normal intake, but this curve is an extrapolation and should be read as one.
Saxenda
Liraglutide, injected daily
| Dose | Appetite remaining | Ceiling on a 2,100 kcal day |
|---|---|---|
| 0.6 mg | 95% | about 1,995 kcal |
| 1.2 mg | 90% | about 1,890 kcal |
| 1.8 mg | 87% | about 1,827 kcal |
| 2.4 mg | 85% | about 1,785 kcal |
| 3 mg | 82% | about 1,722 kcal |
Modelled, not measured. A shorter half life means a flatter curve, and daily dosing spreads the effect rather than concentrating it. No direct intake measurement anchors this table.
Trulicity
Dulaglutide, injected weekly
| Dose | Appetite remaining | Ceiling on a 2,100 kcal day |
|---|---|---|
| 0.75 mg | 95% | about 1,995 kcal |
| 1.5 mg | 90% | about 1,890 kcal |
| 3 mg | 87% | about 1,827 kcal |
| 4.5 mg | 84% | about 1,764 kcal |
Modelled, not measured. Licensed for glycaemic control rather than weight, and the appetite effect is correspondingly mild. No direct intake measurement anchors this table.
Rybelsus
Semaglutide, oral daily
| Dose | Appetite remaining | Ceiling on a 2,100 kcal day |
|---|---|---|
| 3 mg | 90% | about 1,890 kcal |
| 7 mg | 80% | about 1,680 kcal |
| 14 mg | 70% | about 1,470 kcal |
Modelled, not measured. Oral bioavailability is low and variable, so the same molecule taken by mouth suppresses less than the injection at equivalent labelled doses. The shape is inferred from that, not from a trial that measured intake.
Where these come from
- Blundell J et al. Effects of once-weekly semaglutide on appetite, energy intake and control of eating. Diabetes Obes Metab, 2017.
- Friedrichsen M et al. Semaglutide 2.4 mg once weekly on energy intake, appetite and gastric emptying. Diabetes Obes Metab, 2021.
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med, 2021.
- Mifflin MD et al. A new predictive equation for resting energy expenditure. Am J Clin Nutr, 1990.
- Greenway FL. Physiological adaptations to weight loss and factors favouring weight regain. Int J Obes, 2015.
- Arslan S et al. Medical nutrition in the GLP-1 era: protein strategies and lean mass. Clin Nutr ESPEN, 2026.
- Hurtova A et al. Resting metabolic rate fluctuations across the menstrual cycle: a systematic review. Front Physiol, 2026.
Where a dose sits between two measured anchors we interpolate, and where a compounded dose sits above every published tier we apply the strongest known factor rather than extrapolating past the evidence. If you think a figure here is wrong, we would rather hear it than defend it.
A generic calculator gives you one number and no way of knowing whether it fits your life this month. This one shows its working, tells you when the target is beyond what your dose will allow, and moves when your dose, your weight or your cycle moves.