On this page
Formula
Daily calories = BMR × activity factor ∓ (weekly change × 3,500 kcal/lb ÷ 7); BMR = 10W + 6.25H − 5A + 5 (men) or − 161 (women)
- BMR
- basal metabolic rate from the Mifflin-St Jeor equation, in kcal per day
- activity factor
- 1.2, 1.375, 1.55, 1.725 or 1.9, from sedentary to extra active
- weekly change
- the pounds (or kilograms, at about 7,716 kcal/kg) you want to lose or gain per week; subtract for loss, add for gain
- W, H, A
- weight in kg, height in cm and age in years
What the calorie calculator works out
Enter your sex, age, height, weight, activity level and goal, and the calorie calculator returns:
- Daily calories for your goal. What to eat each day to maintain your weight, or to lose or gain it at the weekly rate you chose.
- Maintenance calories. Your estimated total daily energy expenditure (TDEE).
- Daily deficit or surplus. The gap between the target and maintenance.
- BMR and activity factor. The two numbers behind maintenance.
- Other rates. A table of daily targets for losing 0.5 to 2 lb a week and gaining 0.5 or 1 lb a week, with any below the safe minimum marked.
How the daily target is calculated
The calorie calculator works in three steps.
- Resting calories. The Mifflin-St Jeor equation estimates your basal metabolic rate from weight, height, age and sex.
- Maintenance. BMR is multiplied by an activity factor, from 1.2 for a mostly seated day to 1.9 for very hard daily training. The TDEE calculator explains each level.
- Goal adjustment. A pound of body weight is treated as about 3,500 kcal, so each pound per week is 3,500 ÷ 7 = 500 kcal a day. The calculator subtracts that from maintenance to lose weight or adds it to gain.
How to calculate a calorie deficit by hand
Take a 40-year-old man who weighs 210 lb, is 5 ft 10 in tall, exercises lightly and wants to lose 1 lb a week.
- Convert: 210 lb = 95.25 kg; 5 ft 10 in = 70 in = 177.8 cm.
- BMR: 10 × 95.25 + 6.25 × 177.8 − 5 × 40 + 5 = 952.5 + 1,111.25 − 200 + 5 = 1,868.75 kcal/day.
- Maintenance: 1,868.75 × 1.375 = 2,569.6 kcal/day.
- Target: 2,569.6 − 500 = about 2,070 kcal/day.
At 1.5 lb a week he would aim for about 1,820 kcal, and to gain 0.5 lb a week, about 2,820 kcal.
Weekly rate and daily deficit
| Weekly change | Daily deficit or surplus |
|---|---|
| 0.5 lb (0.23 kg) | 250 kcal |
| 1 lb (0.45 kg) | 500 kcal |
| 1.5 lb (0.68 kg) | 750 kcal |
| 2 lb (0.91 kg) | 1,000 kcal |
| 0.25 kg | 276 kcal |
| 0.5 kg | 551 kcal |
| 0.75 kg | 827 kcal |
The CDC notes that people who lose weight gradually, about 1 to 2 lb a week, are more likely to keep it off. For gaining weight, a modest rate such as 0.5 lb a week is easier to sustain and to track.
How low is too low
A common guideline from Harvard Medical School is that intake should not fall below about 1,200 kcal a day for women or 1,500 kcal a day for men, except under the supervision of a health professional. Below those levels it becomes hard to get enough protein, vitamins and minerals from food.
When a target falls below that floor, the calorie calculator still shows the number but adds a warning. That happens most often for smaller, older or less active people who pick a fast rate. The better choices are a slower rate, more daily movement, or a plan made with a doctor or registered dietitian.
Why real results drift from the estimate
The 3,500-calorie rule is a convenient approximation. Research from the NIH, including a 2011 Lancet model by Kevin Hall and colleagues, shows that as you lose weight your energy needs fall, so the same intake produces slower loss over time, and reaching a new stable weight can take a year or more. The NIH Body Weight Planner uses that dynamic model if you want a month-by-month projection.
In practice:
- Weigh yourself regularly and compare the trend over two to three weeks, not day to day.
- If loss stalls, recalculate with your new weight before cutting further.
- Expect early water-weight changes in the first week or two.
Using the result with other calculators
Once you have a target, the macro calculator splits it into grams of protein, carbohydrate and fat. The BMR calculator compares Mifflin-St Jeor with Harris-Benedict and Katch-McArdle, and the BMI calculator shows whether your current and goal weights are in the healthy range for your height.
Common mistakes
- Choosing too high an activity level. This inflates maintenance and hides the deficit. If in doubt, choose the lower level.
- Adding exercise calories back on top. The activity factor already counts exercise.
- Setting a goal weight below the healthy range. Check it against BMI first, and get advice if you are already underweight.
- Holding one number for months. Recalculate after every 10 lb (about 5 kg) of change.
Worked examples
Losing 1 lb a week, US units
A 36-year-old woman, 5 ft 6 in, 172 lb, moderately active, aiming to lose 1 lb a week.
Inputs: Sex = Female; Age = 36 years; Weight = 172; Weight unit = Pounds; Height = 5; Height unit = Feet; Extra inches = 6 in; Activity level = Moderately active (× 1.55): moderate exercise 3–5 days a week; Goal = Lose weight; Weekly rate = 1; Weekly rate unit = Pounds
172 lb = 78.02 kg; 5 ft 6 in = 167.6 cm Mifflin-St Jeor: 10 × 78.02 + 6.25 × 167.6 − 5 × 36 − 161 = 1,487 kcal/day Maintenance = 1,486.9 × 1.55 = 2,305 kcal/day Daily deficit = 0.4536 kg × 7,716.2 kcal/kg ÷ 7 = 500 kcal Target = 2,304.7 − 500 = 1,805 kcal/day
Answer: Calories to lose 1 lb a week: about 1,805 kcal/day (maintenance 2,305 kcal/day). Estimate, not medical advice.
Maintaining weight, metric units
A 47-year-old man, 176 cm, 78 kg, lightly active, who wants to keep his weight steady.
Inputs: Sex = Male; Age = 47 years; Weight = 78; Weight unit = Kilograms; Height = 176; Height unit = Centimeters; Activity level = Lightly active (× 1.375): light exercise 1–3 days a week; Goal = Maintain weight
Mifflin-St Jeor: 10 × 78 + 6.25 × 176 − 5 × 47 + 5 = 1,650 kcal/day Maintenance = 1,650 × 1.375 = 2,269 kcal/day
Answer: Calories to maintain your weight: about 2,269 kcal/day (maintenance 2,269 kcal/day). Estimate, not medical advice.
Edge case: a fast loss rate that falls below the minimum
A sedentary 62-year-old woman, 5 ft 2 in, 130 lb, asking to lose 1.5 lb a week. The result is far below 1,200 kcal, so the calculator warns her to get professional advice.
Inputs: Sex = Female; Age = 62 years; Weight = 130; Weight unit = Pounds; Height = 5; Height unit = Feet; Extra inches = 2 in; Activity level = Sedentary (× 1.2): little or no exercise, desk job; Goal = Lose weight; Weekly rate = 1.5; Weekly rate unit = Pounds
130 lb = 58.97 kg; 5 ft 2 in = 157.5 cm Mifflin-St Jeor: 10 × 58.97 + 6.25 × 157.5 − 5 × 62 − 161 = 1,103 kcal/day Maintenance = 1,102.9 × 1.2 = 1,324 kcal/day Daily deficit = 0.6804 kg × 7,716.2 kcal/kg ÷ 7 = 750 kcal Target = 1,323.5 − 750 = 574 kcal/day
Answer: Calories to lose 1.5 lb a week: about 574 kcal/day (maintenance 1,324 kcal/day). Below the usual minimum; get professional advice first. Estimate, not medical advice.
Assumptions and limitations
- Results are an estimate, not medical advice. Talk to a doctor or registered dietitian before a significant diet change, especially if you have a health condition, are pregnant or breastfeeding, or take medication.
- Maintenance calories are Mifflin-St Jeor BMR × a standard activity factor (1.2 to 1.9), the same method as the TDEE calculator.
- Weight change uses the rule of thumb that 1 lb of body weight equals about 3,500 kcal (about 7,716 kcal per kg), so 1 lb a week is a 500 kcal daily deficit or surplus. Real weight loss usually slows over time as the body adapts.
- The weekly rate is limited to 2 lb (about 0.9 kg). If the target falls below about 1,200 kcal/day for women or 1,500 kcal/day for men, the result warns you to get professional supervision.
- Adults aged 18 to 100 only. Weight must be between 20 and 400 kg and height between 100 and 250 cm.
Frequently asked questions
How do you calculate a calorie deficit?
Estimate your maintenance calories (BMR × activity factor), then decide how fast to lose. Each pound per week needs about 500 kcal a day less, because a pound of body weight is roughly 3,500 kcal. With maintenance of 2,400 kcal, losing 0.5 lb a week means eating about 2,150 kcal.
How many calories should I eat to lose weight?
Start from your maintenance calories and subtract 250 to 1,000 kcal a day for 0.5 to 2 lb a week. Stay at or above about 1,200 kcal a day for women or 1,500 for men unless a health professional is supervising you.
How many calories do I need to gain weight?
Add about 250 kcal a day to maintenance for 0.5 lb a week or 500 kcal for 1 lb a week. A modest surplus with regular strength training helps more of the gain come from muscle.
Is eating 1,200 calories a day safe?
For many women 1,200 kcal is the lowest intake generally advised without supervision, and for men the figure is about 1,500. Whether it suits you depends on your size, health and activity, so check with a doctor or registered dietitian before eating that little.
Why am I not losing weight on my calorie target?
Common reasons are an activity level set too high, underestimated portions, water retention or natural adaptation as weight falls. Track your average weight over two to three weeks; if it has not moved, recalculate with your current weight or cut 100 to 200 kcal a day.
Do men and women need different calories?
The method is the same, but the Mifflin-St Jeor equation gives men 166 kcal a day more at rest than women of the same weight, height and age, and the gap grows with the activity factor. Men are also usually larger, which raises their needs further.
How do you calculate calorie intake for maintenance?
Multiply your BMR by your activity factor. A BMR of 1,450 kcal for someone moderately active (1.55) gives maintenance of about 2,248 kcal a day.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals (Mifflin MD, St Jeor ST et al., Am J Clin Nutr 1990;51:241–7) — American Journal of Clinical Nutrition, via PubMed (NIH). Checked October 10, 2026.
- Steps for Losing Weight — Centers for Disease Control and Prevention (CDC). Checked October 10, 2026.
- Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIH). Checked October 10, 2026.
- Quantification of the effect of energy imbalance on bodyweight (Hall KD et al., Lancet 2011;378:826–37) — The Lancet, via PubMed (NIH). Checked October 10, 2026.
- Calorie counting made easy — Harvard Health Publishing, Harvard Medical School. Checked October 10, 2026.