"How many calories should I eat a day?" is one of the most common questions people type into a search bar, yet most answers online either give you a single flat number (2,000!) or bury you in jargon. This calories-a-day calculator gives you a real, personalized figure based on your body and your lifestyle, using the Mifflin-St Jeor equation — the most widely validated resting-energy formula in healthy adults. Enter your weight in pounds, your height in inches, your age, your biological sex, and how active you are, and the page instantly shows your maintenance calories per day plus the common weight-loss and weight-gain targets.
The headline number you get is your Total Daily Energy Expenditure (TDEE) — the calories you burn on an average day. Eating roughly that many calories keeps your weight stable. Eating below it creates a deficit; eating above it creates a surplus. That is the whole logic behind almost every diet and training plan.
How to Use
- Enter your Weight in pounds. If you know your weight in kilograms, multiply by 2.205 to convert. A morning weigh-in after using the restroom is the most repeatable.
- Enter your Height in total inches. Five feet ten inches is 70 inches; five feet five inches is 65 inches. Do not add a leading 5 — this field wants the full inch count.
- Type your Age in completed years. Basal metabolism naturally slows about 2 percent per decade after adulthood, so leaving your age wrong silently inflates the answer.
- Pick your Biological Sex. Mifflin-St Jeor uses a sex-specific constant: plus 5 for men, minus 161 for women. This is a small but real difference in resting energy expenditure.
- Choose your Activity Level honestly. Most people overestimate themselves. If you sit at a desk and walk only occasionally, pick sedentary (1.2). If you jog or bike three or four days a week, moderate (1.55) is the realistic pick. Gym rats training hard six or seven days a week can move up to very (1.725) or extra (1.9).
- Read the result card. Calories per Day (Maintenance / TDEE) is the number to eat to hold your weight steady. Weight-Loss Target subtracts 500 kcal/day — a deficit that corresponds to roughly 1 pound of fat per week. Weight-Gain Target adds 500 kcal/day for lean-mass gain.
If you are unsure which activity level fits, run the calculator twice — once with sedentary and once with moderate — and split the difference. Most adults land somewhere between the two.
The Formula Behind the Number
Your body burns energy even at rest. That baseline is your Basal Metabolic Rate (BMR), which covers breathing, heartbeat, brain function, and temperature regulation. The Mifflin-St Jeor equation estimates BMR like this:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Because this calculator accepts pounds and inches, it first converts your inputs: kilograms = pounds × 0.45359, and centimeters = inches × 2.54. Then it multiplies BMR by your activity factor to get TDEE. The formula was published in 1990 in the American Journal of Clinical Nutrition and has been compared against indirect calorimetry (the gold-standard measurement) in thousands of adults; it consistently outperforms older equations such as Harris-Benedict.
A quick worked example for a 30-year-old, 180 lb, 5 ft 10 in man who exercises moderately: weight becomes 81.6 kg, height becomes 177.8 cm, BMR = 10(81.6) + 6.25(177.8) − 5(30) + 5 = 1,783 kcal/day. Multiply by 1.55 for moderate activity and you get 2,763 calories per day to maintain weight. A 500-kcal deficit brings the weight-loss target to about 2,263 kcal/day — a level most adults can follow without feeling starved.
Activity Factors, Explained
The multiplier you choose moves the answer more than almost any other input. Here is how the five standard levels map to real life:
- Sedentary (1.2) — desk job, little intentional exercise, walking only to the car and around the house.
- Lightly active (1.375) — light walking, golf, yoga, or easy cycling one to three days a week.
- Moderately active (1.55) — 30 to 60 minutes of brisk walking, jogging, or gym training three to five days a week.
- Very active (1.725) — hard training six or seven days a week, such as running 20+ miles weekly or lifting heavily.
- Extra active (1.9) — physical labor all day plus hard exercise, or elite athletes in heavy training.
Picking a level that is too high makes your maintenance calories look 30–50 percent larger than reality, which is one reason people "eat healthy" and still do not lose weight. When in doubt, round down. A 500-kcal deficit on a 2,763 k/day maintenance target is about 18% of total daily intake — a sustainable cut, not a crash diet.
Examples
Example 1 — A 30-year-old man trying to maintain. 180 lb, 5 ft 10 in, 30 years old, male, moderate activity. The calculator returns a BMR of about 1,783 kcal/day and a maintenance total of 2,763 kcal/day. His weight-loss target of 2,263 kcal/day is a realistic cut that still leaves room for a normal dinner.
Example 2 — A 30-year-old woman losing fat. 150 lb, 5 ft 5 in, 30 years old, female, moderate activity. Her BMR is roughly 1,401 kcal/day and her maintenance total is about 2,172 kcal/day. A 500-kcal deficit brings her to 1,672 kcal/day — still above the 1,200 kcal floor dietitians usually recommend for women, so it is safe to follow.
Example 3 — A sedentary 70-year-old. 130 lb, 5 ft 4 in, 70 years old, female, sedentary. Her BMR is about 1,095 kcal/day and her maintenance total is roughly 1,314 kcal/day. Notice how much lower this is than the headline "2,000 calorie" guideline — age and activity level really do reshape the number, by 20 percent or more.
Example 4 — A hard-training athlete. 200 lb, 6 ft 1 in, 25 years old, male, very active. Maintenance calories can climb above 3,000 kcal/day. Forcing a 500-kcal deficit here still leaves more than 2,500 kcal to eat — plenty of protein, carbs, and vegetables.
FAQ
How many calories should I eat a day to lose weight?
A safe starting point is your maintenance calories from this calculator minus 500 kcal per day. That deficit corresponds to roughly 1 pound (0.45 kg) of fat lost per week. Do not drop below about 1,500 kcal/day for men or 1,200 kcal/day for women without supervision; going lower risks muscle loss, nutrient gaps, and metabolic adaptation.
How many calories should I eat a day to gain muscle?
Add 250 to 500 kcal above your maintenance number. A smaller surplus builds mostly muscle; a larger surplus adds more fat. Most adults on a moderate surplus gain about 0.25 kg per week of lean mass, with beginners gaining faster than advanced lifters.
What is the difference between BMR and TDEE?
BMR is the energy you burn lying motionless all day — your heartbeat, brain, liver, and temperature control. TDEE (total daily energy expenditure) is BMR multiplied by your activity factor, so it includes walking, exercise, chores, and fidgeting. Your BMR is typically 60–70 percent of TDEE for most adults.
Why does this calculator ask for biological sex?
The Mifflin-St Jeor equation was developed on population data and uses a sex-specific constant to account for the higher average lean-muscle mass in men. The gap is about 166 kcal/day at average values. If your body composition is unusual (very high or very low muscle mass), the estimate can be off by 10–15 percent; track your weight for two weeks and adjust the calories up or down by 10 percent until the scale moves as expected.
Is the 2,000-calorie-per-day guideline right for me?
The 2,000 k/day number on Nutrition Facts labels is a round average used for labeling, not a personalized target. A small, sedentary 65-year-old woman may need closer to 1,500 kcal/day, while a tall, active 30-year-old man may need 2,800 kcal/day or more. Use the personalized number this calculator gives you rather than the label average.
How accurate is the Mifflin-St Jeor equation?
In validation studies, Mifflin-St Jeor predicts measured resting energy within about ±10 percent for most healthy adults. It is more accurate than the older Harris-Benedict equation, especially in people carrying extra body fat. The remaining 10 percent gap comes from body-composition differences, genetics, and recent diet — which is why weighing yourself for two weeks and adjusting is the final tuning step.
Should I count calories forever?
Most people do not. The calculation is most useful as a starting point for two to four weeks while you learn portion sizes. After that, many people maintain their weight by habit, plate composition, and the trend of the scale rather than logging every meal. Use this tool when you restart a cut, a bulk, or when your weight has drifted and you need a fresh baseline.
Disclaimer
This calories-a-day calculator is provided for informational purposes only and is not medical advice. The numbers it produces are estimates based on the Mifflin-St Jeor equation and standard activity multipliers; individual needs vary with body composition, genetics, medications, thyroid function, pregnancy, and recent weight changes. This tool does not diagnose, treat, cure, or prevent any disease or eating disorder. If you are managing diabetes, recovering from an eating disorder, pregnant, breastfeeding, or have a chronic condition, please consult a registered dietitian or your physician before changing your calorie intake.