Calorie Calculator — Daily Calories to Lose, Maintain or Gain Weight
Estimate how many calories you need each day to maintain, lose, or gain weight, then see a week-by-week projection to your goal weight that updates your calorie burn as your weight changes — with target dates, macros and safety checks.
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Projected Weight
Daily Calories by Weekly Rate
Starting targets at your current weight. Rates above about 1% of body weight a week are usually too fast to sustain.
| Goal | Daily Calories | Change vs Maintenance | % of Body Weight / Week | Check |
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Macros for Your Target
Protein set by body weight to help preserve muscle, fat at 25–30% of calories, carbohydrate making up the rest.
| Macronutrient | Grams / Day | Calories | % of Calories | Basis |
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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 — your maintenance calories.
BMR (men) = 10W + 6.25H − 5A + 5 · BMR (women) = 10W + 6.25H − 5A − 161 — W = weight in kg · H = height in cm · A = age in years
The projection: your daily target stays fixed, but each week the calculator recalculates your maintenance calories at your new, lower (or higher) weight. The gap shrinks, so progress slows over time — which is closer to real life than assuming the same weekly loss forever. It doesn't model extra metabolic adaptation, water-weight swings or changes in activity, so treat dates as estimates. For a research-grade model, see the NIH Body Weight Planner, based on work by Kevin Hall and colleagues.
By Suhaib Hassan · Reviewed 28 September 2026 against the original equations and NIH guidance · How CalculatePilot verifies formulas →
Using this to lose or gain weight
A deficit of roughly 500–550 calories a day tends to produce about 0.5 kg of weight loss per week at first, since one kilogram of body fat corresponds to roughly 7,700 calories (0.5 × 7,700 ÷ 7 = 550 a day). 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, 80 kg, 178 cm, lightly active: BMR works out to 10 × 80 + 6.25 × 178 − 5 × 35 + 5 = about 1,743 calories, and multiplying by the 1.375 activity factor gives a maintenance level of about 2,396 calories/day.
For illustration, a calorie target can be set below or above maintenance, but the appropriate size of that change depends on the person and goal. The simple energy-balance model used here should not be treated as a guarantee of a particular weekly weight change.
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.
Body composition can affect energy expenditure, but the effect of changing muscle mass on total calorie needs varies between people. Medical information, not medical advice: talk to a doctor or registered dietitian before a substantial dietary change, especially if you're pregnant, under 18 or managing a health condition.
Sources
- Mifflin et al. (1990), A new predictive equation for resting energy expenditure — PubMed
- NIH / NIDDK Body Weight Planner
- Mayo Clinic Calorie Calculator
- Jäger R, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20.
Frequently asked questions
How accurate is this calorie estimate?
It is a predictive estimate, not a direct measurement of energy expenditure. Individual metabolism and activity vary, so use it as a starting point and compare it with your real-world trend over several weeks.
Why does activity level matter so much?
Activity level changes the estimate because everyday movement and exercise contribute to total energy expenditure. The size of that difference varies substantially between people.
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?
There is no single calorie floor that is appropriate for every adult. Very-low-calorie diets can create nutritional and other health risks and should only be undertaken with appropriate clinical 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?
A fixed 500-calorie deficit is not appropriate for everyone. The size of a deficit should be individualized rather than treated as a guaranteed weekly weight-loss formula.
Why does my projected weight loss slow down over time?
Because energy needs can change as body weight, body composition and activity change. The projection is a simplified model and should be compared with real-world trends rather than treated as a guaranteed forecast.
Next Steps
Plan the details of your diet and track progress.