Calories are the unit of energy in food, and your daily need is the number that decides whether your weight rises, falls or stays steady. This calculator estimates that number from your sex, age, height, weight and typical activity, then shows what a moderate surplus or deficit would look like. It uses the Mifflin-St Jeor equation for resting energy and activity levels taken from the US Institute of Medicine, both widely used by dietitians.
No online tool can measure your metabolism. The result is a well-supported starting estimate that you should check against what happens to your weight over a few weeks.
How to use the calorie calculator
- Enter your sex, age, height and weight. The units menu lets you use metric or imperial.
- Pick your activity level honestly. If you are unsure, choose the lower one.
- Read the maintenance figure. Eating around that number should keep your weight roughly steady.
- Look at the loss and gain rows. A change of 500 kcal a day is about 1 lb (0.5 kg) a week on the traditional rule of thumb.
- Check the safety note. It warns when a target drops below the lowest levels in NHLBI guidance.
Calorie formula
Maintenance calories = BMR × activity multiplier
Weight-change target = maintenance ± 250, 500 or 1,000 kcal
The BMR equation is from Mifflin, St Jeor and colleagues (Am J Clin Nutr 1990;51:241–247). A 2005 review for the American Dietetic Association found it the most reliable of several equations in healthy adults. The activity multipliers below are approximations of the Physical Activity Level categories in the Dietary Reference Intakes.
| Activity level (IOM 2005) | PAL range | Multiplier used here | Example: 1,755 kcal BMR |
|---|---|---|---|
| Sedentary | 1.0 – 1.39 | 1.2 | 2,106 kcal |
| Low active | 1.4 – 1.59 | 1.5 | 2,632 kcal |
| Active | 1.6 – 1.89 | 1.75 | 3,071 kcal |
| Very active | 1.9 – 2.5 | 2.2 | 3,861 kcal |
The multipliers are the midpoints of the Physical Activity Level (PAL) categories in the US Institute of Medicine’s Dietary Reference Intakes for Energy (2005): sedentary 1.0–1.39, low active 1.4–1.59, active 1.6–1.89 and very active 1.9–2.5. They are rounded to 1.2, 1.5, 1.75 and 2.2. Your own PAL may sit anywhere inside a band, which is one reason the result is an estimate.
Worked example
A 35-year-old man, 180 cm and 80 kg, who is low active.
- BMR = 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 kcal
- Maintenance = 1,755 × 1.5 = 2,632 kcal
- A 500 kcal deficit = 2,132 kcal a day; a 250 kcal surplus = 2,882 kcal
Daily calories at each activity level
| Person | BMR | Sedentary | Low active | Active | Very active |
|---|---|---|---|---|---|
| Woman 165 cm, 62 kg, 30 y | 1,340 | 1,608 | 2,010 | 2,345 | 2,949 |
| Man 180 cm, 80 kg, 35 y | 1,755 | 2,106 | 2,632 | 3,071 | 3,861 |
Notes on losing or gaining weight
- Small changes work. A deficit of 250 to 500 kcal is easier to keep up than a drastic cut.
- Diet quality counts. Calories set the quantity; protein, fibre and micronutrients set whether you stay healthy. See the Protein Intake Calculator and Macro Calculator.
- Weight loss slows. As you lose weight your maintenance need falls, so recalculate every few kilograms.
- Do not go very low. The NHLBI Practical Guide to the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults (2000) places the usual low-calorie diet at 1,000–1,200 kcal for women and 1,200–1,600 kcal for men, under supervision.
For the resting-energy figure alone use the BMR Calculator, for total daily energy see the TDEE Calculator, and for a goal-date plan use the Calorie Deficit Calculator.
This page is for information only and is not medical or dietary advice. Speak to a doctor or registered dietitian before making large changes to your diet or exercise.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241–247.
- Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105:775–789.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press, 2005 (Physical Activity Level categories).
- NHLBI. The Practical Guide: Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication 00-4084, 2000.
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378:826–837.
Frequently asked questions
How many calories should I eat a day?
It depends on your size, age, sex and activity. This calculator estimates basal metabolic rate with the Mifflin-St Jeor equation and multiplies it by an activity level from the US Institute of Medicine. A 30-year-old woman, 165 cm and 62 kg, who is sedentary, comes out at about 1,610 kcal to maintain her weight.
Is 1,200 calories a day enough?
For many adults it is well below maintenance. The NHLBI Practical Guide to weight loss describes diets of 1,000 to 1,200 kcal for women and 1,200 to 1,600 kcal for men as the usual range for supervised weight loss. Intakes that low can cause nutrient gaps and should be agreed with a doctor or dietitian.
How accurate is this estimate?
The equation predicts resting energy within 10 percent for most people, and the activity multiplier adds uncertainty. Treat the result as a starting point, track your weight and intake for two to three weeks, and adjust by 100 to 200 kcal if your weight does not move as expected.
Why does the calculator use a 500 kcal deficit for a pound a week?
It follows the long-used rule that a pound of body fat holds about 3,500 kcal. Research from Hall and colleagues (Lancet 2011;378:826–837) shows that the rule overstates long-term loss because metabolism slows as weight falls, so real progress usually tapers.
Do I need more calories when I exercise?
Planned exercise raises your total daily need and is what moves you up the activity levels. Choose the level that matches your typical week, not your best week, and avoid also adding the calories burned in a workout on top.