The formulas
resting (women) = 10 × kg + 6.25 × cm − 5 × age − 161 resting (men) = 10 × kg + 6.25 × cm − 5 × age + 5 maintenance = resting × activity factor gradual loss = maintenance − 500
The activity factors are 1.2 (little or no exercise), 1.375 (light), 1.55 (moderate), 1.725 (hard) and 1.9 (very hard or a physical job). For example, a 40-year-old woman who is 5 ft 5 in (165 cm) and 154 lb (70 kg) rests at 10 × 70 + 6.25 × 165 − 5 × 40 − 161 = 1,370 calories. With light exercise that's 1,370 × 1.375 ≈ 1,880 calories a day to stay the same weight.
What the numbers mean
- Resting calories are what your body burns at complete rest: breathing, circulation, keeping warm.
- Maintenance adds daily movement and exercise. Eating about this much keeps weight roughly steady.
- Gradual loss is 500 a day below maintenance, about 3,500 a week. Early on that's close to a pound a week; the body adapts, so the rate slows.
Calories on a GLP-1 medicine
Semaglutide and tirzepatide reduce appetite, so many people eat far less without trying. The risk shifts from eating too much to eating too little to cover protein and nutrients. The 2025 joint advisory on nutrition with GLP-1 therapy recommends paying attention to protein, fiber, fluids and nutrient-dense food rather than cutting calories as far as possible.
Questions
How many calories should I eat to lose weight?
A common starting estimate is about 500 fewer than you burn, which is roughly a pound a week at first. NIH guidance puts weight-loss eating plans at about 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men, and going lower only under medical supervision. Your prescriber or a dietitian can adjust it for you.
How accurate is the Mifflin-St Jeor equation?
It's the equation a systematic review of dietitians' tools found most accurate for most adults, including people with obesity, but it still misses by more than 10% for some people. Treat the result as a starting estimate and adjust it by how your weight actually changes over several weeks.
I'm on a GLP-1 and barely eating. Is that a problem?
Eating very little for a long time makes it hard to get enough protein, vitamins and minerals, and can speed muscle loss. If you're regularly well under 1,200 calories a day, tell your prescriber. The protein and water calculator shows the daily protein range to aim for.
Which activity level should I pick?
Most people with desk jobs who exercise a few times a week fit light or moderate. When unsure, pick the lower level; people tend to overestimate how active they are.
Why does weight loss slow down over time?
A smaller body burns fewer calories, so the same intake becomes a smaller deficit. Re-run the calculator with your new weight every 10 lb or so.