Calorie Calculator
Estimate how many calories you need each day to maintain, lose, or gain weight, based on your body and activity level.
How this calculator works
This calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR), then multiplies it by an activity factor to estimate total daily energy expenditure.
W = weight in kg · H = height in cm · A = age in years
Using this to lose or gain weight
A deficit of roughly 500 calories a day tends to produce about 0.5 kg of weight loss per week, since one kilogram of body fat corresponds to roughly 7,700 calories. The same logic in reverse applies to weight gain.
Why calorie needs vary so much between people
Two people with identical height, weight, and age can still have meaningfully different calorie needs due to differences in muscle mass, genetics, and daily activity outside of formal exercise (often called NEAT — non-exercise activity thermogenesis).
This calculator provides a solid starting estimate, but the most reliable way to find your true maintenance calories is to track your actual weight trend over 2-3 weeks at a consistent intake and adjust from there based on real results. If you're specifically aiming to lose weight, the Weight Loss Calorie Calculator builds a target deficit on top of this number.
A worked example
A 35-year-old man, 80kg, 178cm, lightly active: BMR works out to roughly 1,748 calories, and multiplying by the 1.375 activity factor gives a maintenance level of about 2,404 calories/day.
To lose about 0.5kg/week, subtracting 500 calories gives a target of roughly 1,904 calories/day — while to gain weight at the same rate, adding 500 gives a target of about 2,904 calories/day.
Why calorie needs change over time
As you lose or gain weight, your calorie needs shift too — a smaller body generally burns fewer calories at rest, and a larger body burns more. This is why weight loss often slows over time even at a consistent deficit, and why recalculating every few weeks (rather than once) tends to produce more accurate ongoing targets.
Muscle mass also affects calorie needs meaningfully — muscle tissue burns more calories at rest than fat tissue, which is part of why strength training can help maintain a higher metabolic rate during weight loss compared to cardio alone.
Frequently asked questions
How accurate is this calorie estimate?
It's a well-validated estimate for most people, but individual metabolism varies. Use it as a starting point and adjust based on your actual weight trend over a few weeks.
Why does activity level matter so much?
Activity level scales your baseline metabolic rate to reflect real daily energy use — the difference between sedentary and very active can be 500+ calories a day.
Why am I not losing weight at my calculated deficit?
Common causes include underestimating portion sizes, overestimating exercise calories burned, or a maintenance calorie level that's actually different from the formula's estimate — tracking actual results over a few weeks helps calibrate.
Is it safe to eat below my calculated deficit?
Very low-calorie diets can risk nutrient deficiencies and muscle loss — most guidance suggests not going below roughly 1,200 calories/day for women or 1,500 for men without medical supervision.
Should I recalculate my calorie needs as I lose weight?
Yes — as body weight changes, so does your BMR and total calorie needs, so recalculating every few weeks during an active weight loss or gain phase keeps your target accurate.
Is a 500-calorie deficit always the right target?
It's a common starting point for roughly 0.5kg/week of loss, but very large deficits can be hard to sustain and may risk muscle loss — a moderate, sustainable deficit is generally more effective long-term.