Calorie Calculator – Daily Calorie Needs (Mifflin-St Jeor) Free
Measure — Body
Calorie Calculator
Readout
Daily calorie needs vary enormously from person to person based on body size, age, sex, and activity level — there's no single universal number. This calculator uses the Mifflin-St Jeor equation, widely regarded as the most accurate standard formula for estimating calorie needs, to give you a personalized estimate instantly.
How This Calculator Works: BMR and TDEE
The calculation happens in two steps:
- BMR (Basal Metabolic Rate) — the estimated number of calories your body burns at complete rest just to keep essential functions running (breathing, circulation, cell repair), calculated using the Mifflin-St Jeor equation:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161 - TDEE / Maintenance Calories (Total Daily Energy Expenditure) — your BMR multiplied by an activity factor, giving an estimate of total calories burned in a full day including movement and exercise.
The Mifflin-St Jeor equation is widely cited in clinical and nutrition research as more accurate for most modern populations than the older Harris-Benedict equation it replaced, though like any predictive formula it remains an estimate rather than a direct measurement of your actual metabolism.
Choosing the Right Activity Level
| Level | Description |
|---|---|
| Sedentary | Desk job, little to no structured exercise |
| Lightly active | Light exercise or sports 1–3 days per week |
| Moderately active | Moderate exercise 3–5 days per week |
| Very active | Hard exercise 6–7 days per week |
| Extra active | Physically demanding job, or intense training twice a day |
Most people overestimate their own activity level, which is one of the most common reasons calorie calculators produce estimates that don't match real-world results — choosing a more conservative activity level and adjusting based on actual outcomes over a few weeks tends to be more reliable than guessing high from the start.
Calorie Targets for Weight Loss or Gain
According to the CDC's guidance on healthy weight management, gradual, steady weight loss of about 1–2 pounds per week is generally recommended over rapid loss, since it tends to be more sustainable long-term. A pound of body fat represents roughly 3,500 calories, so a sustained daily deficit of about 500 calories translates to roughly 1 pound of weight loss per week — the basis for the "Lose" and "Gain" estimates this calculator provides alongside your maintenance number.
Why This Number Is an Estimate, Not a Guarantee
Even the most accurate standard equation can't account for everything that affects individual metabolism — genetics, muscle mass, hormonal factors, certain medications, and metabolic adaptation over time can all shift real calorie needs meaningfully above or below the formula's prediction. Treat the result as a starting point to test and adjust from, based on how your actual weight trends over several weeks, rather than a fixed, guaranteed number.
Frequently Asked Questions
Is the Mifflin-St Jeor equation the most accurate calorie formula?
It's widely regarded in nutrition research as more accurate for most people than the older Harris-Benedict equation, though all predictive formulas remain estimates rather than a direct measurement of individual metabolism.
Why did my calorie result change when I picked a different activity level?
Activity level is a multiplier applied to your BMR, so even a small change in selected activity level can shift the total maintenance calorie estimate by several hundred calories, since daily movement can represent a large share of total energy use.
Should I eat below 1,200 calories a day to lose weight faster?
Very low calorie intakes are generally discouraged without medical supervision, since they can be difficult to meet nutritionally and are often not sustainable long-term. The CDC recommends gradual, steady weight loss of about 1–2 pounds per week rather than rapid restriction.
Does this calculator work for pregnant or breastfeeding women?
No — calorie needs during pregnancy and breastfeeding are significantly different and should be discussed directly with a healthcare provider rather than estimated with a general calculator like this one.
Why am I not losing weight even though I'm eating at my calculated deficit?
This is common and usually comes down to slightly underestimating food intake, overestimating activity level, water retention masking fat loss short-term, or a metabolism that runs somewhat differently from the formula's prediction. Tracking actual weight trends over several weeks, and adjusting the estimate based on real results, is more reliable than relying on the initial number alone.
Is my personal data stored anywhere?
No. All calculations happen instantly in your browser using JavaScript. Nothing is uploaded, logged, or sent to a server.
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