Calorie Deficit Calculator
Pick a weight-loss pace and this shows the daily calories to aim for — your maintenance number minus a sensible deficit. Simple, and grounded in the same math dietitians use.
Your numbers stay in your browser — nothing is sent or saved.
How the deficit works
Weight loss comes from eating fewer calories than you burn. This tool estimates your maintenance calories (TDEE) with the Mifflin–St Jeor formula, then subtracts a deficit sized to your chosen pace — using the common rule that about 3,500 calories ≈ 1 pound. It won't let the target drop below a safer floor, because eating too little backfires.
Deficits and GLP-1 medications
On a GLP-1 the appetite reduction often creates a deficit naturally — sometimes a bigger one than is ideal. Using a target helps you avoid under-eating, which costs muscle and energy. Pair your calorie target with a protein goal and resistance training, and see the realistic weight-loss timeline.
Frequently asked questions
How big should my calorie deficit be?
About 500 cal/day is a common, sustainable deficit (~1 lb/week). Bigger deficits are harder to hold and can cost muscle; keep intake above ~1,200 (women) / ~1,500 (men) without supervision.
How many calories is one pound?
Roughly 3,500 calories ≈ 1 lb, so a 500/day deficit ≈ ~1 lb/week. It's a rule of thumb, not an exact law.
Why won't the calculator go lower?
Very low intakes are unsafe and backfire, so the tool holds a safer floor. To go faster, do it under medical or dietitian supervision.
Do I still need a deficit on a GLP-1?
Yes — the deficit is still what drives loss; the GLP-1 just makes it easier to reach. On a GLP-1 the bigger risk is under-eating, so a target helps you fuel enough.
Sources & further reading
- Mifflin MD, St Jeor ST, et al. — resting energy expenditure equation.
- Common '3,500 kcal ≈ 1 lb' estimate; note real energy balance is more complex.
- Academy of Nutrition and Dietetics — safe rates of weight loss.