Calorie deficit calculator
Losing weight comes down to one idea: eat a little less than you burn. This free calculator does the two-step maths for you. First it estimates your maintenance calories (your TDEE) from your age, sex, height, weight, and activity level using the Mifflin-St Jeor formula. Then it subtracts the daily deficit you choose — a gentle 250, a moderate 500, a faster 750, or a custom number — and shows your target intake plus a realistic estimate of how much you would lose each week. Everything updates instantly as you type, in metric or imperial, with no account or email. The goal is a deficit you can actually live with: sustainable beats aggressive every time, and the weekly figure is an estimate to steer by, not a promise.
Your daily calorie target
1,750 kcal/day
Maintenance 2,250 kcal − 500 kcal deficit · about 0.45 kg (1.0 lb) per week (estimate)
How the deficit calculation works
Weight change follows energy balance. Eat the same calories you burn and your weight holds; eat fewer and your body draws on stored energy. This calculator works in two steps.
Step one — maintenance calories. We estimate your TDEE (total daily energy expenditure) with the Mifflin-St Jeor equation, then a standard activity multiplier:
TDEE = (10 × kg + 6.25 × cm − 5 × age + s) × activity
s = +5 men, −161 women · activity 1.2 → 1.9
Step two — the deficit. We subtract your chosen daily deficit from maintenance to get your target: target = TDEE − deficit. For the weekly estimate we use the well-known approximation that about 3,500 calories is roughly 0.45 kg (1 lb) of body weight, so a 500 kcal daily deficit works out to around 0.45 kg a week.
Two honest caveats. That 3,500-calorie rule is a rule of thumb, not a law of physics — real loss depends on water, muscle, hormones, and how closely you stick to the plan, and the scale naturally zig-zags. And a bigger deficit is not automatically better: very aggressive cuts are hard to maintain and can sap energy. Pick a deficit you can hold for weeks, and read your progress as a trend, not a daily verdict.
Frequently asked questions
What is a calorie deficit?
A calorie deficit means eating fewer calories than your body burns in a day. When that happens consistently, your body makes up the difference from stored energy, and you lose weight over time. This tool finds your maintenance calories first, then subtracts the deficit you choose.
How big a deficit should I aim for?
A deficit of 250–500 calories a day is a common, sustainable range for most people — roughly 0.25–0.45 kg (about 0.5–1 lb) per week. Larger deficits lose weight faster but are harder to maintain and can cost you energy and muscle. Slower and steady usually wins.
How accurate is the weekly weight estimate?
It is an estimate based on the rule of thumb that about 3,500 calories equals roughly 0.45 kg (1 lb) of body weight. Real results vary with water balance, muscle, sleep, and adherence, and weight loss rarely moves in a straight line. Judge progress over several weeks, not day to day.
Estimate a real plate instead
Numbers are a start — logging is where progress happens. Snap a photo of your meal and NibbleCal estimates the calories and macros in about 3 seconds.
Try it with a photo — free, no signup