Calorie Calculator

Understanding BMR vs. TDEE

Every daily calorie target starts with two numbers most people mix up. Your BMR — basal metabolic rate — is the energy your body burns at complete rest to keep your heart beating, your lungs breathing, and your brain online. Your TDEE — total daily energy expenditure — is what you actually burn in a 24-hour window once you add movement, digestion, and training. TDEE is the number you plan around; BMR is the floor you can never safely eat below.

Three equations dominate the field. The Mifflin-St Jeor formula (1990) is the modern default: it predicts BMR within roughly ten percent for about seventy percent of adults and is what CalStory ships by default. The Revised Harris-Benedictequation (Roza & Shizgal, 1984) is the older clinical standard and tends to over-shoot modern populations by around five percent. The Katch-McArdleformula (1996) is the only one of the three that asks for your body-fat percentage, because it works directly from lean mass. When your body-fat number is accurate, Katch-McArdle is the most precise of the three. When it's a guess, stick with Mifflin.

The equations, side by side

• Mifflin-St Jeor (1990). Men: 10 · kg + 6.25 · cm − 5 · age + 5. Women: 10 · kg + 6.25 · cm − 5 · age − 161.
• Revised Harris-Benedict (1984). Men: 88.362 + 13.397 · kg + 4.799 · cm − 5.677 · age. Women: 447.593 + 9.247 · kg + 3.098 · cm − 4.330 · age.
• Katch-McArdle (1996). 370 + 21.6 · (kg · (1 − bodyFatPct/100)). Sex-independent.

TDEE is just BMR scaled by your weekly activity. A sedentary desk worker multiplies by about 1.2, a four-days-a-week lifter by about 1.55, and someone who trains twice a day or works a physical job by 1.9. The calculator above uses those exact multipliers and lets you swap between the three BMR formulas with one click.

How many calories do you actually need?

Five variables drive the answer: age, sex, height, weight, and activity. Age and sex are fixed; the other three are levers you can move. A 30-year-old male who is 180 cm and 80 kg burns more than a 60-year-old female who is 160 cm and 60 kg at the same activity level — sometimes by a thousand calories a day. General population ranges for maintenance calories, taken from the published Mifflin-St Jeor validation cohorts, look roughly like this:

• Sedentary men: ~1,900–2,200 kcal/day. Sedentary women: ~1,500–1,800 kcal/day.
• Moderately active men: ~2,400–2,800 kcal/day. Moderately active women: ~1,900–2,200 kcal/day.
• Very active men: ~3,000–3,500 kcal/day. Very active women: ~2,400–2,800 kcal/day.

Muscle mass shifts the same person's BMR upward by roughly six to ten kcal per pound of additional lean tissue, because muscle is metabolically active and fat is not. Two people who weigh the same on the scale can burn meaningfully different calories at rest.

Floor warning. The body needs a minimum amount of energy to keep its organs running. For most adult women that floor is around 1,200 kcal/day; for most adult men it's around 1,500 kcal/day. Going meaningfully below those floors for more than a few days without medical supervision risks muscle loss, hormonal disruption, and the metabolic slowdown that makes a crash diet backfire. The calculator won't show you anything below maintenance, but it also can't warn you when maintenance itself is below your real needs — that's a conversation to have with a clinician if you suspect under-eating. For a deeper primer on the unit itself, see what a calorie actually is.

A practical guide to calorie counting

Calorie counting works because energy balance is the only mechanism that decides whether body weight goes up, down, or nowhere. But the math is only half the job; the rest is process. Five steps, in order:

1. Calculate your BMR. Use Mifflin-St Jeor as the default, switch to Katch-McArdle if you have a recent DEXA or caliper body-fat number. The calculator above does this for you.
2. Set a deficit or surplus. Subtract 250–500 kcal for a fat-loss target, add 200–400 kcal for muscle gain. Bigger swings work in the short term but cost muscle, energy, and adherence.
3. Pick a tracking method. The best tracker is the one you still open in week three. Beginners do best with AI food logging — describing a meal in plain English gets you out of the database scrolling that kills most trackers by day ten.
4. Log consistently, not perfectly. Restaurant meals will be guesses, home meals will be precise, and that mix is fine. Logging a placeholder is always better than logging a zero, because the streak survives.
5. Reassess weekly. A seven-day rolling average is the only signal worth reading. Daily weight bounces two to four pounds on water and sodium alone; the trend line is the truth.

CalStory is built around those five steps. The AI food logger handles step three, the dashboard calorie ring handles step four, and the weekly recalibration in your settings handles step five — your target drifts up or down by 100 kcal depending on whether your actual weight change is matching the planned rate.

Safe rate of weight loss

The famous 3,500 kcal ≈ 1 lb of fat rule is a simplification, but a useful one. A daily 500-calorie deficit adds up to 3,500 kcal over a week, which lines up with roughly one pound of fat lost. A 250-calorie deficit produces about half a pound per week, which is the gentle end of the spectrum. Those numbers assume the deficit comes from intake, not from over-training on top of an already low baseline.

Most coaches cap fat loss at roughly one percent of bodyweight per week. For a 180-pound adult that's about 1.8 lb/week; for a 130-pound adult it's about 1.3 lb/week. Going meaningfully faster than that has three predictable costs:

• Muscle loss. Aggressive cuts cannibalize lean tissue alongside fat. The classic study from Garthe et al. (2011) showed faster weight loss produced more muscle loss than slower weight loss even at the same total deficit.
• Hormonal drag. Testosterone drops, cortisol rises, thyroid function slows. None of that is good for a lifter trying to keep strength in a cut.
• Metabolic adaptation. The body down-regulates BMR to defend its set-point. The more aggressive the cut, the more the down-regulation, and the harder the eventual reverse-diet becomes.

A standard 500-kcal/day cut runs about a pound a week and is the sweet spot for most lifters. Anything below a 750-kcal/day deficit should be paired with medical sign-off. For a deeper look at the mechanics of running a deficit without losing muscle, see what a calorie deficit actually is.

Calorie quality: not all calories are equal

A calorie is a unit of energy and nothing else — but the food that delivers that energy changes how your body uses it. Three brief notes:

• Whole vs. processed. Whole foods tend to be high-volume and high-fiber, which means you can eat more of them for the same calories and feel fuller. A 300-calorie chicken-and-rice bowl fills most people; a 300-calorie pastry rarely does.
• The thermic effect of food. Protein costs roughly 20–30% of its calories to digest; carbs cost 5–10%; fat costs 0–3%. That means 100 kcal of chicken effectively contributes about 70–80 usable kcal — a meaningful gap over months of tracking.
• Empty-calorie sources.Sugary drinks and alcohol deliver calories without meaningful satiety. A 12-oz soda (≈150 kcal) doesn't suppress the next meal; a sandwich of the same calories does. The same logic applies to fruit juice versus whole fruit.

None of this contradicts energy balance. Two people on the same daily calorie target will see different hunger, energy, and body composition depending on where those calories come from. Aim for the high-quality bulk of your calories first; the last 10% is fine-tuning.

Zigzag / calorie cycling

Zigzag (or calorie cycling) means varying daily calorie intake while hitting the same weekly average. A 14,000-kcal week works out to 2,000 kcal/day if every day is identical, but it also works out to 1,800 kcal four days a week paired with 2,600 kcal three days a week. Same weekly total, different daily shape.

Why bother? Three reasons. First, social occasions rarely line up with your deficit day — front-loading calories for a Saturday dinner removes the friction of saying no to a restaurant. Second, training days and rest days have genuinely different energy needs, so eating to the training day makes the deficit feel less restrictive. Third, the psychological novelty of a higher-calorie day helps long-term adherence — most people find a flat 1,800 kcal harder to sustain than a 1,500–2,100 swing that averages to the same place.

Zigzag isn't magic. If the weekly average matches your goal and you can sustain it, the daily shape is a personal-preference dial. CalStory's daily calorie ring stays accurate whether you zig or zag, because the underlying target is the same and the recalibration uses your seven-day average weight.

Related tools and guides

The Calorie Calculator is one of three free tools on CalStory. The best macro calculator splits a daily calorie target into protein, carbs, and fat — once you have a TDEE number, the next decision is how to spend it. For the underlying maintenance math, the calorie-deficit deep-dive on the About page walks through the same Mifflin equation with more clinical context. New tool pages for BMR-only and BMI calculations are queued for the next round of updates.