Quick answer: your daily calorie need is your resting burn (BMR) times an activity factor. With the Mifflin-St Jeor equation, a 30-year-old woman who is 165 cm and 62 kg has a BMR of about 1,340 kcal; with moderate exercise (× 1.55) she maintains her weight on roughly 2,080 kcal a day. Eating about 500 kcal less leads to roughly 0.5 kg loss a week.
BMR and TDEE in plain words
BMR (basal metabolic rate) is what your body burns lying still all day – breathing, heartbeat, keeping warm. TDEE (total daily energy expenditure) adds everything else: walking, work, exercise and digesting food. TDEE is your “maintenance” number: eat about that much and your weight stays roughly the same.
The equation used
This calculator uses Mifflin-St Jeor, which studies found to be the most accurate of the common formulas for most adults:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The result is multiplied by an activity factor from 1.2 (sedentary) to 1.9 (very physical job plus training). Most people overestimate their activity – if you sit most of the day and train three times a week, “light” or “moderate” is usually right.
Turning the number into a plan
| Goal | Daily change | Typical pace |
|---|---|---|
| Mild weight loss | −250 kcal | ≈ 0.25 kg (½ lb) a week |
| Weight loss | −500 kcal | ≈ 0.5 kg (1 lb) a week |
| Maintenance | 0 | Weight stays steady |
| Weight gain | +250 to +500 kcal | Slow gain, best with strength training |
These are averages. Water, hormones and how much you move change the scale from day to day, so judge progress over two to three weeks, not two to three days.
Not sure what weight to aim for? Check your range with the BMI calculator first, then come back to set a daily calorie target that fits.
How to work out your daily calories
- Enter sex, age, height and weight. Use metric or imperial units – the formula converts for you.
- Pick your honest activity level. Count your typical week, not your best week.
- Read maintenance calories. This is the amount that keeps your weight about the same.
- Choose a gentle target. For weight change, start with 250–500 kcal below or above maintenance and review after a few weeks.
When to get personal advice
Formulas are estimates for healthy adults. If you are pregnant or breastfeeding, under 18, managing a medical condition, or if thinking about food and weight feels stressful, please speak to a doctor or registered dietitian rather than following a calculator.
Worked example
A 35-year-old man, 180 cm and 80 kg, with a desk job and no regular exercise:
- BMR = 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 kcal.
- Sedentary factor 1.2: 1,755 × 1.2 = 2,106 kcal to maintain weight.
- For about 0.5 kg loss a week: 2,106 − 500 ≈ 1,600 kcal a day.
If he starts walking 45 minutes on five days a week, “light” activity (× 1.375) puts maintenance at about 2,410 kcal – the same loss pace at around 1,900 kcal.
Common mistakes
- Counting exercise twice – the activity factor already includes your workouts; don’t add fitness-tracker calories on top.
- Choosing “very active” for three gym sessions – that level is for daily hard training or physical jobs.
- Cutting too much – big deficits are hard to keep and can cost muscle; slow and steady usually lasts.
Frequently asked questions
How many calories should I eat a day?
Roughly your TDEE to stay the same weight. Many adults fall between 1,800 and 2,600 kcal, but height, weight, age and activity move it a lot.
Which BMR formula is used?
Mifflin-St Jeor, which is widely recommended for adults and tends to be closer than the older Harris-Benedict equation.
How accurate is this calculator?
For most people it is within about 10%. Track your weight for a few weeks and adjust the number up or down.
How many calories are in a kilogram of fat?
About 7,700 kcal (3,500 per pound), which is where the 500-kcal-a-day guideline for 0.5 kg a week comes from.
Should I eat my BMR?
No. BMR is what you burn at complete rest. Eating below it for long periods is not recommended without medical supervision.
Does it work for teenagers?
It is designed for adults. Teenagers are still growing and should get advice from a doctor or dietitian.
Do I need to count calories to lose weight?
No. Knowing your rough maintenance number helps you judge portions; many people succeed with simple habits rather than exact counting.
Why has my weight stopped changing?
As you lose weight, your maintenance calories fall too. Recalculate with your new weight every few kilograms.