How many calories should you eat in a day?
There's no single right answer, and anyone who gives you one without asking about your body first is guessing. Your daily calorie needs depend on your size, age, sex, and, more than anything else, how much you move. A 25-year-old builder and a 60-year-old office worker of the same weight can easily be a thousand calories apart.
What this calorie calculator does is narrow the guess down. It estimates how much energy your body burns in a typical day, then shifts that number up or down depending on whether you want to lose weight, hold steady, or gain. The result is a starting target, and a good one — but your own scale over the following weeks is the final judge.
How this calorie calculator works
Under the hood is the Mifflin-St Jeor equation, published in 1990 and still the formula the American Academy of Nutrition and Dietetics considers the most reliable for estimating resting metabolism in most adults. It calculates your basal metabolic rate (BMR) — the calories your body burns just keeping you alive:
Men: BMR = 10 × kg + 6.25 × cm − 5 × age + 5
Women: BMR = 10 × kg + 6.25 × cm − 5 × age − 161
Take a 30-year-old woman, 70 kg and 170 cm. Her BMR works out to 700 + 1,062.5 − 150 − 161, which is roughly 1,452 calories. That's what she'd burn lying in bed all day. Since almost nobody lies in bed all day, the calculator then multiplies BMR by an activity factor to get your total daily energy expenditure, or TDEE. At a moderate activity level her TDEE lands around 2,250 calories.
If you're curious about the resting number on its own, the BMR calculator breaks it down in more detail, and the TDEE calculator focuses on the full daily burn.
Calorie needs by activity level
The activity multiplier is where most people get their estimate wrong, and almost everyone errs in the same direction: overestimating. Be honest here. A desk job plus two gym sessions a week is 'light', not 'active'.
| Activity level | Multiplier | What it looks like |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little or no exercise |
| Lightly active | × 1.375 | Exercise 1–3 days a week |
| Moderately active | × 1.55 | Exercise 3–5 days a week |
| Active | × 1.725 | Hard exercise 6–7 days a week |
| Very active | × 1.9 | Physical job plus hard training |
Calories for weight loss, maintenance, and weight gain
Once your TDEE is known, the goal math is straightforward. Eat roughly what you burn and your weight holds. Eat less and it falls; eat more and it rises. This calculator offers three paces in each direction: a gentle 250-calorie shift, a standard 500, and an aggressive 1,000.
The old rule of thumb says a pound of fat stores about 3,500 calories, so a 500-calorie daily deficit should cost you about a pound a week. Reality is messier — your body adapts, water weight muddies the scale, and the rate slows over time — but as a planning figure it still works.
A word of caution on the aggressive settings: a 1,000-calorie deficit is a lot, and for smaller or lighter people it can drop intake below what's sensible without medical supervision. If the calculator gives you a target under about 1,200 calories, that's a sign to slow the pace down, not push through.
Where your macro numbers come from
Alongside calories, the results panel splits your target into protein, fat, and carbohydrate. The split shifts with your goal: cutting weight biases toward protein (about 35% of calories) because protein protects muscle and keeps you full; gaining tilts toward carbs (about 45%) to fuel training; maintenance sits in between.
These ratios are sensible defaults, not laws. If you want to fine-tune them — say, more protein while cutting — the macro calculator and protein calculator let you dial in each one separately.
Treat the number as a starting point
Every calorie formula, this one included, is an estimate built from population averages. Your genetics, hormones, sleep, medication, and gut all nudge your real burn away from the textbook figure — usually by a little, occasionally by a lot.
The fix is simple and doesn't require a lab: eat at your target for two to three weeks and watch the trend on the scale. Losing faster than planned? Add 100–200 calories. Not moving at all? Trim the same amount. Two or three rounds of that and you'll know your real number better than any calculator can tell you.
Frequently asked questions about calories
How many calories should I eat per day?
It depends on age, sex, size, activity, and goals. Maintenance calories match your TDEE. Weight loss usually means eating below TDEE; weight gain means eating above it.
How big should a calorie deficit be for weight loss?
A deficit of about 300–500 calories below TDEE is a common starting point — roughly 0.5–1 lb per week. Larger deficits should be supervised by a professional.
Are online calorie calculators accurate?
They estimate based on formulas and your inputs. Genetics, hormones, sleep, and medical conditions shift real needs. Track weight trends and adjust after 2–3 weeks.
When should I get professional nutrition advice?
See a dietitian or doctor if you have diabetes, kidney disease, pregnancy, an eating disorder history, or if calorie changes are not producing expected results.
How do I use this calorie calculator?
Enter your stats and activity level, pick a goal (lose, maintain, or gain), and click Calculate to see daily calorie targets.
Sources and further reading
- Mifflin MD et al. — A new predictive equation for resting energy expenditure (Am J Clin Nutr, 1990)
- CDC — Losing weight at a healthy pace
- NIH — Body Weight Planner
- Dietary Guidelines for Americans
This page is for general information only and is not medical or dietary advice. Talk to a qualified professional before making major changes to how you eat.