Calorie Calculator

What "how many calories should I eat" is really asking

There is no single correct number of calories. There is a number that holds your current weight, and then a range around it. Everything else is a choice about how fast you want to move.

This calculator answers the question in three steps:

1. How much do you burn at rest? That's your basal metabolic rate (BMR) — the cost of being alive, breathing, and keeping organs running. For most adults it's 60–70% of daily burn.
2. How much do you burn on top of that? Movement, exercise, digesting food, and fidgeting. Together these multiply BMR by an activity factor between 1.2 and 1.9.
3. What do you want to do about it? Hold, lose, or gain — and how fast, which sets the size of the daily calorie change.

The third step is where most calorie calculators stop. This one shows all three targets at once, because the honest answer to "how many calories should I eat" is three numbers and a pace.

The calculation, step by step

The default profile — female, 35, 5'5", 150 lb, lightly active, goal 140 lb — runs like this:

BMR (Mifflin-St Jeor) = 10 × 68.04 kg + 6.25 × 165.1 cm − 5 × 35 − 161
                      = 680.4 + 1,031.9 − 175 − 161
                      = 1,376 kcal

TDEE = 1,376 × 1.375 (lightly active)
     = 1,892 kcal

Target (lose 1 lb/week) = 1,892 − 500
                        = 1,392 kcal

The 500-calorie step comes from the standard approximation that 3,500 calories of deficit ≈ 1 lb of body weight. One pound per week is 3,500 ÷ 7 = 500 calories per day. Half a pound is 250; two pounds is 1,000.

At 1,392 calories, a balanced split lands on roughly 104 g protein, 139 g carbs, and 46 g fat per day.

Three goals, three targets

Same person, same day, different goal:

Two rows in that table are marked as problems by the calculator. At 1,142 and 892 calories she is below the 1,200-calorie floor that's commonly used as the minimum for unsupervised dieting, and the page shows a warning instead of quietly handing over the number. That's not a moral judgment about willpower — it's that intakes that low are hard to hit while getting enough protein, fiber, and micronutrients, and the deficit usually collapses within weeks.

Activity level is the biggest lever

Two people with identical bodies can differ by nearly 1,000 calories a day purely on how much they move. That's larger than the entire deficit most people are trying to create, which is why guessing your activity level is the single most common source of error.

*Below the recommended minimum intake for this profile.

Notice what the sedentary row implies: at a desk job, the same person cannot run a 500-calorie deficit without dropping under the floor. The fix is not a smaller target — it's more movement. Forty minutes of walking adds roughly the same deficit without cutting food.

The other thing worth noticing: the difference between "light" and "moderate" is 241 calories a day, which is about 25 lb of body weight over a year if you consistently guess wrong in the same direction.

How to pick your level honestly

• Sedentary — desk job, under 5,000 steps most days, no structured exercise.
• Lightly active — 1–3 workouts a week, or a job that keeps you on your feet part of the day.
• Moderately active — 3–5 workouts a week, or 8,000–10,000 steps most days.
• Very active — training 6–7 days a week, or a physically demanding job plus training.
• Extra active — hard physical labor plus daily training, or two-a-day sessions.

If you're between two levels, take the lower one. Most people overestimate.

When body fat changes the answer

Mifflin-St Jeor uses height, weight, age, and sex — it has no idea whether you're carrying 15% or 40% body fat, and fat tissue burns far less than muscle. If you know your body fat percentage, the calculator switches to Katch-McArdle, which runs entirely off lean mass:

BMR = 370 + 21.6 × lean body mass (kg)

For the same 150 lb woman:

At 30% body fat the two formulas nearly agree, so the choice doesn't matter much. At 40% they differ by 124 calories a day — because at 40% body fat the Mifflin formula is over-crediting her with metabolically cheap tissue. That's 12 lb a year of drift if you're cutting and 12 lb if you're gaining.

Leave the field blank if you don't have a real measurement. Guessing a body fat percentage is worse than using Mifflin, because it moves the target without adding information.

The 1,200 and 1,500 calorie floors

The calculator flags any target below 1,200 calories for women and 1,500 for men. These are widely used minimums from weight-management guidance, not physiological limits — people do go lower under medical supervision. They're a practical line for three reasons:

1. Nutrient density. Below roughly 1,200 calories it becomes hard to hit protein, fiber, iron, calcium, and the B vitamins without deliberate planning.
2. Adherence. Very low intakes produce hunger that most people can't sustain for the weeks a real loss requires.
3. Lean mass. Aggressive deficits — especially without resistance training and adequate protein — take a meaningful share of the loss from muscle rather than fat.

If your target comes out under the floor, the calculator's suggestion is to slow the pace or add activity, not to eat less.

Reading the macro split

The 30/40/30 split shown under your target is a starting point, not a prescription:

• Protein 30% — at 1,392 calories that's 104 g, or about 1.5 g per kg of body weight. Reasonable for most people; if you're training hard, the protein intake calculator works it out from body weight instead of from calories, which is the more reliable way.
• Carbs 40% — 139 g. Carbs are the fuel most people cut first, and the first thing to restore if training quality drops.
• Fat 30% — 46 g. Below about 0.5 g/kg of body weight, hormone production and vitamin absorption can suffer.

The percentage split matters far less than total calories and total protein. If you want to shift it, the macro calculator has four presets including low-carb and keto.

Where this estimate goes wrong

Four sources of error, roughly in order of size:

1. Under-reported intake. Doubly labeled water studies consistently find people under-report what they eat by 20–30%. The calculator isn't wrong; the log is.
2. Overestimated activity. Covered above — this is the one you can fix in ten seconds.
3. Adaptive thermogenesis. Long deficits reduce spontaneous movement and slightly lower BMR, so real-world loss slows relative to the 3,500-calorie rule. Expect the last 10 lb to take longer than the first 10.
4. The 3,500-calorie rule itself. It was derived in 1958 and assumes the loss is nearly all fat. Early weight loss includes water and glycogen, which is why the first week often looks dramatic and the third looks stuck.

The right way to use any calorie target is as a starting hypothesis: eat at it for two to three weeks, track weight at the same time each morning, average the week, and adjust by 100–200 calories based on what actually happened.

How to use this calculator

1. Pick US or metric units.
2. Enter sex, age, height, and weight.
3. Optionally add body fat percentage to switch to Katch-McArdle.
4. Choose the activity level that matches your normal week, not your best week.
5. Pick a goal and a pace.
6. Optionally enter a goal weight to see how many weeks the pace implies.
7. Read the target, then check the activity table and the floor warning before committing.

Frequently asked questions

How many calories should I eat to lose weight?

Take your maintenance number and subtract 500 for 1 lb a week, or 250 for 0.5 lb a week. For a lightly active 35-year-old woman at 5'5", 150 lb, maintenance is 1,892, so 1 lb a week means 1,392 calories a day.

How many calories do I need a day to maintain my weight?

That's your TDEE: BMR × activity factor. For the same 150 lb woman it's 1,892. A 175 lb moderately active man at 5'9" needs about 2,703, and a highly active 200 lb man at 6'0" needs about 3,157.

Is 1,200 calories a day enough?

For most adults it's the lower bound of what's sensible without supervision, and it's below maintenance for nearly everyone — so it will produce loss, but usually not the kind you keep. A 5'5", 150 lb woman eating 1,200 calories is running a 692-calorie daily deficit, which is 1.4 lb a week, well beyond the pace her target of 1,392 implies.

Why is my calorie target different from another calculator?

Different BMR equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) and different activity multipliers. Mifflin-St Jeor is the equation most current guidance recommends for general use. Differences of 100–200 calories between tools are normal and usually reflect the activity factor, not the formula.

Should I eat back the calories I burn exercising?

Only if your activity level doesn't already include that exercise. If you set "moderately active" because you train four days a week, the training is already in the multiplier — eating back workout calories on top double-counts them.

Can I lose weight faster than 2 lb a week?

You can lose weight faster; the question is what you lose. Beyond roughly 1% of body weight per week, a larger share of the loss comes from lean tissue, and the deficit becomes hard to hold. Two pounds a week is a reasonable ceiling for most people with a lot to lose, and too aggressive for someone already lean.

Does the calculator work for teenagers or pregnancy?

No. Growth, pregnancy, and lactation change energy needs in ways this model doesn't represent. Those cases need individual guidance from a clinician or registered dietitian.

Data sources: BMR uses the Mifflin-St Jeor equation (Mifflin et al., Am J Clin Nutr, 1990) — 10 × kg + 6.25 × cm − 5 × age + 5 for men, − 161 for women — or Katch-McArdle (370 + 21.6 × lean kg) when body fat is entered. Activity multipliers are the five standard values 1.2 / 1.375 / 1.55 / 1.725 / 1.9. The 3,500 kcal per pound figure is the Wishnofsky approximation (1958) and is treated here as a rule of thumb. Intake floors of 1,200 kcal (women) and 1,500 kcal (men) follow common weight-management guidance. Every figure on this page can be reproduced by entering the same inputs (female, 35, 5'5", 150 lb, lightly active, lose 1 lb/week).

Disclaimer: This calculator is a general estimate for reference and is not medical or nutritional advice. Actual energy needs vary with body composition, medical conditions, medications, and how much you move. If you are pregnant, breastfeeding, under 18, or managing a condition such as diabetes or kidney disease, talk to a clinician before changing your intake. Related tools: TDEE calculator, BMR calculator, calorie deficit calculator, calorie calculator for weight loss, all health calculators.