Your daily calorie needs are your TDEE (total daily energy expenditure): your BMR × an activity multiplier. Your BMR (basal metabolic rate) comes from the Mifflin-St Jeor formula — for men, BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; for women, the same formula ends in − 161 instead of + 5. For example, a 30-year-old man weighing 80 kg (176 lb) and 180 cm tall (about 5’11”) has a BMR of 1,780 calories a day, and at a moderate activity level he needs about 2,759 calories a day to maintain his weight. This guide explains both formulas, works through examples for a man and a woman step by step, and shows how to adjust the result for weight loss or gain.
If you want the answer for your own numbers without doing the arithmetic, use the free calorie calculator — enter your age, sex, weight, height and activity level and it computes your BMR and TDEE instantly.
What Is the Difference Between BMR and TDEE?
Your BMR is the energy your body burns at complete rest — the calories needed just to keep your heart beating, lungs breathing and temperature steady, before any movement at all. Your TDEE is the realistic number: BMR plus everything you actually do in a day, from walking to the bus stop to a gym session.
- BMR — basal metabolic rate: calories burned at total rest. Calculated from your sex, weight, height and age.
- TDEE — total daily energy expenditure: BMR × an activity multiplier between 1.2 and 1.9. This is your maintenance calorie level.
- Maintenance: eat at your TDEE and your weight stays roughly the same. Eat below it and you lose weight; eat above it and you gain.
Several BMR formulas exist. The Mifflin-St Jeor equation, published in 1990, is the one most dietitians and calculators use today because it has proven the most accurate for the general adult population — the Academy of Nutrition and Dietetics found it predicts measured resting metabolic rate more closely than the older Harris-Benedict formula for most people.
What Is the Mifflin-St Jeor Formula?
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
The only difference between the two is the final constant: +5 for men, −161 for women, reflecting average differences in body composition. Everything is in metric units — if you think in pounds and inches, convert first (pounds ÷ 2.205 = kilograms; inches × 2.54 = centimeters), or let the calculator handle it.
How Do You Calculate Your BMR? Step-by-Step Examples
Worked example — man: age 30, 80 kg (176 lb), 180 cm (about 5’11”).
- Weight term: 10 × 80 = 800.
- Height term: 6.25 × 180 = 1,125.
- Age term: 5 × 30 = 150.
- Add the constant for men: +5.
- BMR = 800 + 1,125 − 150 + 5 = 1,780 calories per day.
Worked example — woman: age 30, 65 kg (143 lb), 165 cm (about 5’5″).
- Weight term: 10 × 65 = 650.
- Height term: 6.25 × 165 = 1,031.25.
- Age term: 5 × 30 = 150.
- Subtract the constant for women: −161.
- BMR = 650 + 1,031.25 − 150 − 161 = 1,370.25, or about 1,370 calories per day.
Notice what drives the numbers: weight and height push BMR up, age pulls it down slowly (5 calories per year of age), and the sex constant accounts for the roughly 400-calorie gap between these two examples, on top of their size difference.
How Do You Turn BMR Into Daily Calorie Needs (TDEE)?
Multiply your BMR by the activity factor that best matches your typical week — be honest, because most people overestimate this step, and it is the biggest source of error in the whole calculation.
| Activity level | What it looks like | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | × 1.2 |
| Lightly active | Light exercise or sports 1–3 days a week | × 1.375 |
| Moderately active | Moderate exercise 3–5 days a week | × 1.55 |
| Very active | Hard exercise 6–7 days a week | × 1.725 |
| Extra active | Very hard exercise daily, or a physical job plus training | × 1.9 |
Applied to the two worked examples:
| Activity level | Man (BMR 1,780) | Woman (BMR 1,370) |
|---|---|---|
| Sedentary (× 1.2) | 2,136 | 1,644 |
| Lightly active (× 1.375) | 2,448 | 1,884 |
| Moderately active (× 1.55) | 2,759 | 2,124 |
| Very active (× 1.725) | 3,071 | 2,364 |
| Extra active (× 1.9) | 3,382 | 2,604 |
So the man in the example, training moderately, maintains his weight at about 2,759 calories a day, while the woman, if she is lightly active, maintains at about 1,884 calories a day. Same formulas — the difference comes from body size and activity, not from any special rule.
How Many Calories Do You Need to Lose or Gain Weight?
Once you know your TDEE, the adjustment is simple arithmetic. A common, sustainable approach is to shift your intake by about 500 calories a day:
- To lose weight: TDEE − 500. A deficit of 500 calories a day adds up to about 3,500 calories a week, which corresponds to roughly 1 lb (about 0.45 kg) of body fat per week — a steady rate most people can sustain. For the man above: 2,759 − 500 = 2,259 calories a day.
- To gain weight or build muscle: TDEE + 250 to + 500, ideally paired with resistance training so the surplus goes toward muscle rather than only fat. For the man above: 2,759 + 500 = 3,259 calories a day at the upper end.
- To maintain: eat at your TDEE and adjust by 100–200 calories if your weight drifts for two weeks or more — real bodies vary, and the formula is an estimate, not a measurement.
Two safety notes. First, very low intakes are counterproductive and risky: as a general floor, women should not go below about 1,200 calories a day and men about 1,500 without medical supervision. On that rule, the woman in the example (maintenance 1,884, lightly active) would use a smaller deficit — around 1,384 calories a day would come from the full 500 cut, so a gentler cut is the safer choice. Second, if you have a medical condition, are pregnant, or are under 18, these general formulas are not a substitute for professional advice.
How Do Macronutrients Fit Into Your Calorie Target?
Calories decide whether you gain or lose; macronutrients decide what the change is made of. A balanced starting split is 30% protein, 40% carbohydrates and 30% fat. Protein and carbohydrates provide 4 calories per gram, fat provides 9. For the man’s 2,759-calorie maintenance target:
- Protein: 2,759 × 0.30 ÷ 4 = about 207 g per day.
- Carbohydrates: 2,759 × 0.40 ÷ 4 = about 276 g per day.
- Fat: 2,759 × 0.30 ÷ 9 = about 92 g per day.
Where does BMI fit in? Your calorie needs come from your actual weight, whatever it is. If you first want to see where your current weight sits — underweight, healthy, overweight or obese on the standard CDC categories — check it with the free BMI calculator, then use the calorie figures above to plan the change.
That is the full method: Mifflin-St Jeor gives your BMR, the activity multiplier turns it into your real daily needs (TDEE), and a modest surplus or deficit steers your weight from there. Run your own figures through the free calorie calculator, treat the result as a starting estimate, and fine-tune it against two or three weeks of real weight change — that feedback loop is what makes the number truly yours.
Frequently Asked Questions
What is the formula for calculating daily calorie needs?
First calculate your BMR with the Mifflin-St Jeor formula — men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; women: the same, ending in − 161 — then multiply by an activity factor from 1.2 (sedentary) to 1.9 (extra active). The result is your TDEE, the calories that maintain your current weight.
How many calories does a 30-year-old man need per day?
It depends on size and activity. A 30-year-old man at 80 kg (176 lb) and 180 cm (about 5’11”) has a BMR of 1,780 calories. His maintenance needs range from 2,136 calories a day if sedentary to 3,382 if extra active — about 2,759 at a moderate activity level.
How many calories does a 30-year-old woman need per day?
A 30-year-old woman at 65 kg (143 lb) and 165 cm (about 5’5″) has a BMR of about 1,370 calories. Her maintenance needs range from 1,644 calories a day if sedentary to 2,604 if extra active — about 1,884 at a light activity level.
How many calories should I eat to lose weight?
A common sustainable target is your TDEE minus about 500 calories a day, which adds up to roughly 1 lb (about 0.45 kg) of weight loss per week. For a man maintaining at 2,759 calories, that is about 2,259 a day. Avoid going below about 1,200 calories a day for women or 1,500 for men without medical supervision.
What is the difference between BMR and TDEE?
BMR is the energy your body burns at complete rest, before any activity. TDEE is BMR multiplied by an activity factor (1.2 to 1.9), so it reflects a real day. BMR is an input to the calculation; TDEE is the number you actually eat against.
How accurate is the Mifflin-St Jeor formula?
It is the most accurate widely used estimate for the general adult population — research reviewed by the Academy of Nutrition and Dietetics found it predicts measured resting metabolic rate within 10% for more non-obese and obese adults than other common formulas. It is still an estimate: track your weight for two to three weeks at your calculated TDEE and adjust by 100–200 calories if it drifts.
