# How many calories do I need a day?

Estimates the calories a day an adult needs to keep their weight (BMR × activity factor), and the daily targets to lose or gain 0.5 to 2 pounds a week.

- Page: https://www.acalculator.org/health/calorie-calculator
- JSON spec: https://www.acalculator.org/health/calorie-calculator.json
- Version: fb42db2fd930

## Default answer

Example with the default inputs (Sex Female, Age 30, Height 5 ft 5 in, Weight 150 lb, Activity Light: exercise 1 to 3 days, BMR formula Mifflin-St Jeor): You need about 1,927 calories a day to keep your current weight.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| sex | Sex | Sex at birth, which the body formulas use. |
| age | Age | Your age in whole years. |
| height | Height | Your height without shoes. |
| weight | Weight | Your body weight. |
| activity | Activity | How active you are in a usual week, which sets the multiplier on your BMR. |
| formula | BMR formula | The equation for basal metabolic rate: Mifflin-St Jeor (1990) or the revised Harris-Benedict (1984). |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| maintain | Calories to keep your weight | Estimated calories a day to keep your current weight: BMR × activity factor. |
| mildLoss | Lose 0.5 lb (0.23 kg) a week | Calories a day to lose about half a pound a week: 250 fewer than to keep your weight. |
| loss | Lose 1 lb (0.45 kg) a week | Calories a day to lose about one pound a week: 500 fewer than to keep your weight. |
| fastLoss | Lose 2 lb (0.91 kg) a week | Calories a day to lose about two pounds a week: 1,000 fewer than to keep your weight. |
| mildGain | Gain 0.5 lb (0.23 kg) a week | Calories a day to gain about half a pound a week: 250 more than to keep your weight. |
| gain | Gain 1 lb (0.45 kg) a week | Calories a day to gain about one pound a week: 500 more than to keep your weight. |
| bmr | BMR (calories at complete rest) | Basal metabolic rate: the calories a day your body uses at complete rest. |
| limit | Note | Which loss targets are left out because they fall below the lowest intake the guideline suggests. |

## Method

Calories to keep your weight = BMR × activity factor, with BMR from Mifflin-St Jeor (10 × kg + 6.25 × cm − 5 × age + 5, or − 161 for women) or the revised Harris-Benedict; each 500 calories a day less loses about 1 lb a week.

## Assumptions

- The formulas are for adults (Mifflin-St Jeor was fitted on people aged 19 to 78). They are not for children, pregnancy or breastfeeding.
- Activity factors: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725, extra active 1.9.
- A pound of body weight is taken as 3,500 calories, so 500 fewer calories a day is about 1 lb a week. Real loss slows over time as your needs fall.
- Loss targets under 1,200 calories a day (women) or 1,500 (men) are left out, the low end of the diets in the 2013 AHA/ACC/TOS guideline.
- This is an estimate for planning, not medical advice.

## Worked examples

1. sex = female, age = 30, height = 1.651, weight = 68.038856, activity = light, formula = mifflin gives bmr = 1,401.263555, maintain = 1,926.737388, mildLoss = 1,676.737388, loss = 1,426.737388, gain = 2,426.737388, limit = Losing 2 lb a week would mean eating under 1,200 calories a day, below the lowest diet the weight-loss guideline suggests.. Source: Mifflin et al. 1990 and the 1.375 activity factor; hand calculation in content.mdx.
2. sex = male, age = 35, height = 1.778, weight = 81.646627, activity = moderate, formula = mifflin gives bmr = 1,757.716266, maintain = 2,724.460212, fastLoss = 1,724.460212, mildGain = 2,974.460212. Source: Mifflin et al. 1990 and the 1.55 activity factor; hand calculation in content.mdx.
3. sex = female, age = 40, height = 1.65, weight = 60, activity = sedentary, formula = harris gives bmr = 1,340.383, maintain = 1,608.4596. Source: Roza and Shizgal 1984 (revised Harris-Benedict) and the 1.2 activity factor; hand calculation in content.mdx.
4. sex = female, age = 60, height = 1.55, weight = 50, activity = sedentary, formula = mifflin gives maintain = 1,209.3, limit = Losing 0.5 lb, 1 lb or 2 lb a week would mean eating under 1,200 calories a day, below the lowest diet the weight-loss guideline suggests.. Source: Mifflin et al. 1990; AHA/ACC/TOS 2013 guideline (1,200 kcal a day for women); hand calculation in content.mdx.

## FAQ

### How many calories do I need a day?

It depends on your size, age, sex and activity. This calculator first estimates your basal metabolic rate (BMR), the calories your body uses at rest, then multiplies it by an activity factor from 1.2 (sedentary) to 1.9 (extra active). For example, a 30-year-old woman who is 5 ft 5 in, weighs 150 lb and exercises 1 to 3 days a week needs about 1,927 calories a day to keep her weight.

### How many calories should I eat to lose weight?

A common rule is that a pound of body weight holds about 3,500 calories, so eating 500 fewer calories a day than you burn loses about 1 pound a week. The calculator shows targets for 0.5, 1 and 2 pounds a week. The CDC notes that people who lose about 1 to 2 pounds a week are more likely to keep the weight off.

### Why are some weight-loss targets missing?

The 2013 guideline from the American Heart Association, the American College of Cardiology and The Obesity Society suggests weight-loss diets of 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men. When a target would fall under 1,200 (women) or 1,500 (men) calories a day, the calculator leaves it out and says so. Eating less than that should be done only with a health professional.

### Which BMR formula should I choose?

Mifflin-St Jeor is the default. A 2005 systematic review found it predicted resting metabolic rate within 10% of the measured value in more healthy adults than the other equations it tested. The revised Harris-Benedict equation (1984) is also offered for comparison. It usually gives a higher BMR, by up to about 350 calories a day for heavy people.

### How accurate is this estimate?

It is a starting point. Equations based on height, weight, age and sex can be off by 10% or more for a given person, and the activity factor is a broad guess. Track your weight for a few weeks: if it moves when you want it steady, adjust your calories by 100 to 200 a day.

### Does my calorie need change as I lose weight?

Yes. A lighter body burns fewer calories, so the same intake gives a smaller deficit over time and weight loss slows. Enter your new weight every few weeks. The weight loss calculator shows how this slowing plays out over months.

## 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):241-247. https://doi.org/10.1093/ajcn/51.2.241
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182. https://doi.org/10.1093/ajcn/40.1.168
- 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):775-789. https://doi.org/10.1016/j.jada.2005.02.005
- FAO/WHO/UNU. Human energy requirements (2004), section 5.3.1, Classification of physical activity levels (PAL = TEE ÷ BMR). https://www.fao.org/4/y5686e/y5686e07.htm
- Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542-546. https://doi.org/10.1093/ajcn/6.5.542
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults. Circulation. 2014;129(25 Suppl 2):S102-S138. https://pmc.ncbi.nlm.nih.gov/articles/PMC5819889/
- Centers for Disease Control and Prevention. Steps for Losing Weight. https://www.cdc.gov/healthy-weight-growth/losing-weight/index.html