Calorie calculator: how much energy you use in a day
Updated on
Enter your age, height, weight and how active you are: the calculator estimates the energy you use in a day, as a range, with the Mifflin St Jeor formula. It is an estimate, not a measurement. Everything is calculated on your device and nothing is sent anywhere.
How the calculation works
Two steps. First, the energy your body uses at rest, with the formula published by Mifflin and colleagues in 1990 from measurements of 498 healthy adults:
- Male formula: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
- Female formula: 10 × weight in kg + 6.25 × height in cm − 5 × age − 161
Then, this energy at rest is multiplied by a physical activity level. We use the three lifestyle categories of the 2004 FAO, WHO and UNU report on human energy requirements:
- Sedentary or light activity: 1.40 to 1.69
- Active or moderately active: 1.70 to 1.99
- Vigorously active: 2.00 to 2.40 (the report notes that higher levels are hard to keep up for long)
The bottom and the top of your category give the range. Values are rounded to 10 kcal.
Examples
| Profile | At rest | Sedentary or light | Moderately active |
|---|---|---|---|
| Female formula, 30 years old, 165 cm (5 ft 5 in), 60 kg (132 lb) | 1,320 kcal | 1,850 to 2,230 kcal | 2,240 to 2,630 kcal |
| Male formula, 40 years old, 180 cm (5 ft 11 in), 80 kg (176 lb) | 1,730 kcal | 2,420 to 2,920 kcal | 2,940 to 3,440 kcal |
| Female formula, 65 years old, 160 cm (5 ft 3 in), 70 kg (154 lb) | 1,210 kcal | 1,700 to 2,050 kcal | 2,060 to 2,420 kcal |
How far to trust the result
- The formula: a 2005 systematic review found Mifflin St Jeor to be the equation most often within 10% of measured energy at rest, with noteworthy errors for some people. Older adults and some ethnic groups were underrepresented in the studies.
- Your body: the formula does not know how much muscle you have. Two people of the same height and weight can use different amounts of energy.
- Your activity: choosing the category is the biggest guess. If you hesitate, pick the lower one.
- The real check: note what you eat and your weight for a few weeks. If your weight stays stable, what you eat is close to your real needs.
Eating a little less or a little more
Below the range on screen, the calculator shows neutral adjustments: about 10% less, about 20% less and about 10% more, from the middle of your range. It shows no timeline and makes no weight loss promise: how your body responds varies from one person to the next. Note that about 10% less lands close to the bottom of your maintenance range: that is how wide the uncertainty is.
It never shows a reduction below your energy used at rest or below 1,200 kcal a day. The NICE guideline on overweight and obesity (2025) reserves eating 800 to 1,200 kcal a day for people followed by a specialist service. The WHO body mass index (BMI) thresholds set the rest: under 18.5 (underweight), no reduction at all; from 18.5 to 25 (normal weight), only about 10% less; about 20% less only from a BMI of 25.
Who this calculator is not for
- People under 18, whose needs depend on growth.
- People who are pregnant or breastfeeding.
- People with diabetes, kidney disease, a thyroid condition or another medical condition, or following a meal plan set by a doctor.
- Anyone with an eating disorder, past or present, or a difficult relationship with food. If food or your weight takes up a lot of your thoughts, a calorie number will not help: talk to a doctor.
FotoMeal gives estimates, not medical advice. See our terms of use.
Your numbers stay on your device
The calculation runs in your browser, in a small script you can read (/assets/calc-v1.js). It sends no request, sets no cookie, stores nothing and adds nothing to the page address. Nothing you type is ever tracked.
Following your goal in FotoMeal
In FotoMeal, your daily goal is 2,000 kcal by default and you can change it to the result above. Then you photograph your meals, scan barcodes or search for foods, and the app adds up your day against that goal. Barcode, search and the journal are free; the photo scan comes with a 7-day trial.
Questions
How accurate is this calculator?
It gives an estimate. In a 2005 systematic review, the Mifflin St Jeor formula was the one most often within 10% of measured resting expenditure, but it can be further off for a given person. That is why the result is a range.
Why a range instead of one number?
Because your activity level is itself a range, and the formula has a margin of error. A single number to the calorie would suggest a precision nobody has.
Why does the calculator show no reduction under 1,200 kcal?
The NICE guideline on overweight and obesity (2025) reserves eating 800 to 1,200 kcal a day for people followed by a specialist service. The calculator also never shows a reduction below your resting expenditure, none at all if your BMI is under 18.5, and only about 10% less if it is between 18.5 and 25.
Can I use it if I am pregnant, breastfeeding or under 18?
No. The formula was not built for these situations: needs depend on pregnancy, breastfeeding or growth. Ask a doctor, a midwife or a dietitian.
Do you save what I type?
No. The calculation runs on your device. Nothing is sent, nothing is stored, and nothing goes into the page address.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-7.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-89.
- FAO, WHO, UNU. Human energy requirements, report of a joint expert consultation, 2004, section 5.3.1, table 5.3.
- NICE. Overweight and obesity management (NG246), 2025, recommendations 1.16.8 to 1.16.11.
- WHO. Body mass index (underweight among adults: BMI under 18.5).
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