Calorie Calculator

A calorie calculator estimates how many calories a day keep your weight steady, then adds or subtracts from that number for loss or gain. A moderately active 35-year-old woman who is 5 ft 6 in and 150 lb needs about 2,158 calories a day to maintain her weight. At 1 lb a week, reaching 140 lb would take about 10 weeks.

How to use the calorie calculator

1. Choose US or metric units, then enter your sex, age, height and current weight.
2. Pick the activity level that matches a normal week.
3. Add a goal weight if you have one, and choose a weekly rate of change.
4. Read your maintenance calories at the top. Below them are the daily calories by goal, the goal planner with weeks to your goal and the calories that will maintain your goal weight.
5. Switch to Calories from macros to turn grams of protein, carbohydrate and fat into calories. Choose Kilojoules if you count energy in kJ.

How many calories do you need a day?

Your daily need has two parts. Your basal metabolic rate (BMR) is the energy your body uses at complete rest. Everything you do on top of that, from walking to the store to a workout, raises the total. The calculator estimates both:

Maintenance calories = BMR × activity multiplier

BMR comes from the Mifflin-St Jeor equation, where W is weight in kilograms, H is height in centimeters and A is age in years:

• Women: BMR = 10W + 6.25H − 5A − 161
• Men: BMR = 10W + 6.25H − 5A + 5

It was built from measurements of 498 healthy adults aged 19 to 78. The activity multipliers run from 1.2 for a mostly seated day to 1.9 for very hard exercise or a physical job. They are a widely used convention, not measured values, so treat the result as a first estimate. If your weight stays steady for a few weeks at a known intake, that intake is a better guide than any formula.

Calories to lose or gain weight

The table of daily calories by goal sets each target a fixed distance from your maintenance level: 250 or 500 calories below for loss and 250 or 500 above for gain. These are plain differences. The calculator deliberately does not promise a number of pounds per week for each one. The popular rule that 3,500 calories equal one pound treats weight change as a straight line, but your needs fall as your weight falls, so real progress slows over time. The NIH’s Body Weight Planner uses a dynamic model of body weight change to build a calorie plan tied to a date.

For pace, USDA’s Nutrition.gov calls 1 to 2 pounds per week a reasonable rate of weight loss. The CDC notes that people who lose weight at about that pace are more likely to keep it off. That is why the rate choices stop at 2 lb (0.9 kg) a week. If a target in the table falls below your estimated BMR, the calculator marks it in red. Eating that little is not something to try without a doctor or dietitian.

Goal weight timeline formula

The goal planner uses simple arithmetic:

Weeks to goal = |goal weight − current weight| ÷ weekly rate

It also reruns the BMR equation at your goal weight. This gives the calories that will maintain your new weight once you reach it.

For weight loss, the planner marks two milestones. The NIDDK suggests a first goal of losing 5% to 10% of your starting weight within 6 months. The CDC notes that even modest loss, such as 10 pounds for a person who weighs 200, can improve blood pressure, cholesterol and blood sugar.

Worked calorie examples

Example 1: maintenance and a 10 lb goal (US units)

A 35-year-old woman is 5 ft 6 in, weighs 150 lb, is moderately active and wants to reach 140 lb at 1 lb a week.

1. Convert: 150 × 0.45359237 ≈ 68.04 kg, and 66 in × 2.54 = 167.64 cm.
2. BMR = 10(68.04) + 6.25(167.64) − 5(35) − 161 ≈ 1,392.1 calories.
3. Maintenance = 1,392.1 × 1.55 ≈ 2,158 calories a day. The loss target is 2,158 − 500 = 1,658 and the mild-loss target is 1,908.
4. Timeline: (150 − 140) ÷ 1 = 10 weeks, or about 2.3 months. Her 5% milestone, 7.5 lb, comes at 7.5 weeks.
5. At 140 lb (63.5 kg), BMR ≈ 1,346.8 and 1,346.8 × 1.55 ≈ 2,088 calories a day, 70 fewer than today.

Example 2: a metric goal of 10 kg

A 40-year-old man is 178 cm, weighs 95 kg, is lightly active and wants to reach 85 kg at 0.5 kg a week.

1. BMR = 10(95) + 6.25(178) − 5(40) + 5 = 1,867.5 calories.
2. Maintenance = 1,867.5 × 1.375 ≈ 2,568 calories a day. The goal table reads 2,318 (mild loss) and 2,068 (loss).
3. Timeline: 10 ÷ 0.5 = 20 weeks, about 4.6 months. 5% of 95 kg is 4.75 kg, reached at 9.5 weeks, and 10% (9.5 kg) at 19 weeks, both within 6 months.
4. At 85 kg, BMR = 1,767.5 and maintenance ≈ 2,430 calories a day, 138 fewer than at the start.

Example 3: calories from macronutrients

A day with 120 g protein, 250 g carbohydrate and 70 g fat:

1. Protein: 120 × 4 = 480. Carbohydrate: 250 × 4 = 1,000. Fat: 70 × 9 = 630.
2. Total: 480 + 1,000 + 630 = 2,110 calories.
3. Shares: 480 ÷ 2,110 ≈ 23% protein, 1,000 ÷ 2,110 ≈ 47% carbohydrate and 630 ÷ 2,110 ≈ 30% fat.

Calories per gram of protein, carbohydrate and fat

USDA’s Agricultural Research Service gives the standard energy values used on food labels:

Fat carries more than twice the energy of the same weight of protein or carbohydrate.

Calories and kilojoules

A food “calorie” is a kilocalorie (kcal). Many countries label food in kilojoules (kJ) instead. The calculator uses the NIST value for the thermochemical kilocalorie: 1 kcal = 4.184 kJ. So 2,158 kcal is about 9,028 kJ, and to go the other way you divide kilojoules by 4.184.

Common calorie calculator mistakes

• Overstating activity. Pick the level for a typical week. If you are torn between two, the lower one is usually closer.
• Expecting a straight line. Weight change slows as you get closer to your goal, and water weight makes day-to-day numbers jump. Judge progress over weeks.
• Never recalculating. Your maintenance level falls as your weight falls. Rerun the numbers after every few kilograms or pounds.
• Forgetting that fat is 9, not 4. Counting fat at 4 calories per gram undercounts it by more than half.

These numbers are estimates for healthy adults, not medical or nutrition advice. Talk with a doctor or registered dietitian before big changes to how you eat, especially if you are pregnant, breastfeeding, under 18 or managing a health condition. Health professionals can also use the USDA’s DRI Calculator for estimated calorie needs based on the Dietary Reference Intakes.

Sources

All sources checked November 2026.

• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247 (PubMed)
• USDA Nutrition.gov: rate of weight loss
• CDC: Steps for Losing Weight
• NIDDK (NIH): Choosing a Safe and Successful Weight-loss Program
• NIDDK (NIH): Body Weight Planner and Research Behind the Body Weight Planner (Hall KD et al., Lancet 2011)
• USDA Agricultural Research Service: Going Nuts Over Calories (4, 4 and 9 calories per gram)
• NIST Guide to the SI, Appendix B.9 (kilocalorie to joule)
• USDA National Agricultural Library: DRI Calculator for Health Professionals

Calorie practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How many calories should I eat a day?

Start with your maintenance number from the calculator. That is the intake estimated to keep your weight about the same. There is no single right number for everyone, because it depends on your size, age, sex and activity, so your own result is more useful than an average.

How many calories should I eat to lose weight?

Eat below your maintenance level. The goal table shows 250 and 500 calories below as starting points. Then watch your weight for a few weeks and adjust. USDA and CDC describe 1 to 2 pounds a week as a reasonable pace. The NIH Body Weight Planner can build a date-based plan.

How long will it take to reach my goal weight?

Divide the weight you want to change by your weekly rate. Losing 15 lb at 1 lb a week takes about 15 weeks. Real progress usually slows near the end, so treat the date as a rough guide.

Why does the calculator not use the 3,500-calorie rule?

The rule assumes every 3,500 calories you cut removes exactly one pound, week after week. In reality your calorie needs drop as you lose weight, so the same deficit produces less loss over time. The calculator gives calorie differences and lets you choose a rate rather than linking them with that rule.

How do I convert calories to kilojoules?

Multiply kilocalories by 4.184. For example, 2,000 kcal × 4.184 = 8,368 kJ. To convert kilojoules back to calories, divide by 4.184.

Related calculators

• Unit converter for pounds, kilograms, inches and centimeters
• Date calculator to count weeks to a target date
• Percentage calculator for 5% and 10% of your starting weight
• Percent change calculator to track a change in weight or calories