Calorie Deficit Calculator

How the calculator works

A deficit is nothing more than eating less than you burn. Arriving at the number takes three steps:

1. What you burn at rest, from the Mifflin-St Jeor equation [1] — of the predictive equations in common use, the one that holds up best in healthy adults:
   Male: 10 × kg + 6.25 × cm − 5 × age + 5
Female: 10 × kg + 6.25 × cm − 5 × age − 161
2. What you burn across the whole day, by multiplying that resting figure through an activity factor [4]: ×1.2 if sedentary, ×1.375 lightly active, ×1.55 moderately, ×1.725 very, ×1.9 for a physical job plus hard training.
3. The gap itself, on the old approximation that a pound of body fat is worth about 3,500 kcal. Working back, rate × 3,500 ÷ 7 is the daily shortfall that produces a given rate — 500 kcal a day for a pound a week, 1,000 for two. What you eat is then just TDEE − daily deficit.

The safety floor

Wider is not better. Nothing here will send a woman below roughly 1,200 kcal a day or a man below 1,500 [3]. Ask for a rate that would breach that and the target stops at the floor instead, and you are told the slower rate you can actually expect from it. Going under the floor unsupervised buys you nutrient deficiencies, lost muscle, and a metabolism that adapts downward until progress stops.

Why the estimate isn't a guarantee

Treating 3,500 kcal as a pound is fine for planning and wrong in detail. Energy balance moves as you do [2]: a lighter body burns less, so the same intake buys you less loss as the months pass. Meanwhile water, salt, sleep, stress, medication and where you are in a menstrual cycle all push the scale about from one day to the next. Start from these numbers, then let 2 to 4 weeks of your own data correct them.

Where GLP-1 medications fit in

The arithmetic above is the easy half. Holding a deficit while hunger climbs against you is the half that defeats people, and it is precisely what GLP-1 medications like semaglutide and tirzepatide act on: appetite falls, the stomach empties more slowly, and the same target stops feeling like a fight. For what the trials say that is worth at your starting weight, see our GLP-1 weight loss calculator. Where the deciding question is price, compare the cheapest semaglutide options.

Important disclaimer

Educational only. Nothing here diagnoses, treats, or advises. The calorie figures are population averages and your own metabolism may sit some way off them. Take a weight-loss plan to a clinician or a registered dietitian before you begin it — and certainly do so if you are pregnant or breastfeeding, under 18, an older adult, or living with a chronic condition.

Related tools

• GLP-1 weight loss calculator — what the trials recorded for semaglutide, tirzepatide and orforglipron, applied to your own figures
• GLP-1 BMI calculator — the BMI band you are in now, and where each trial endpoint would put you
• Best semaglutide providers — vetted telehealth options ranked
• Cheapest semaglutide — lowest cash-pay prices compared