Find your calorie needs, your calorie deficit target, and a realistic timeline to your goal weight. Pick from Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle. Free, no signup required.
BMR calculator: what you burn doing nothing
BMR is basal metabolic rate, the calories your body spends in a day if you did nothing but lie still. It's most of what you burn. Two of the formulas here estimate it from height, weight, age, and sex. The third works from lean mass instead, which is why it asks for a body fat percentage.
Mifflin-St Jeor (1990): 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women.
Harris-Benedict, 1984 revision: 13.397 × kg + 4.799 × cm − 5.677 × age + 88.362 for men, or 9.247 × kg + 3.098 × cm − 4.330 × age + 447.593 for women.
Katch-McArdle: 370 + 21.6 × lean body mass in kg, where lean mass is your weight with the body fat taken out.
Worked example, on the calculator's defaults: a 30 year old man, 180 pounds, 5 foot 9. Mifflin-St Jeor gives about 1,767 calories a day. Harris-Benedict gives about 1,853. Katch-McArdle at 20% body fat gives about 1,781. Three formulas, a 86 calorie spread, and none of them has met him.
TDEE calculator: rest plus everything else
TDEE is total daily energy expenditure: your BMR times an activity multiplier, which is the physical activity level approach the FAO, WHO, and UN University laid out. The multiplier is the part you pick yourself, and it's where most of the error comes from, because almost everyone picks one level too high.
Activity multipliers, and the TDEE each gives on the example's Mifflin-St Jeor BMR of 1,767
Activity level
What it means
Multiplier
Example TDEE
Sedentary
Little to no exercise
× 1.2
2,120 a day
Lightly Active
Light exercise 1-3 days/week
× 1.375
2,430 a day
Moderately Active
Moderate exercise 3-5 days/week
× 1.55
2,739 a day
Very Active
Hard exercise 6-7 days/week
× 1.725
3,048 a day
Extremely Active
Athlete-level daily training
× 1.9
3,357 a day
The calculator defaults to sedentary. If you sit most of the day and train three times a week, that is closer to lightly active than moderately active. When in doubt, pick the lower one and let the scale argue you up.
Maintenance calories calculator: the same number, asked differently
Your maintenance calories are your TDEE. Eat that many on average and your weight holds. People search for it as a separate tool, but there's nothing separate to compute: the TDEE above is your maintenance, and every deficit or surplus is measured from it.
What the formula can't give you is your maintenance, as opposed to the average for people shaped like you. That takes a few weeks of logged weight and calories, which is what the forecast is for.
Calorie deficit calculator: from a gap to a date
A calorie deficit is eating under maintenance. This calculator uses 3,500 calories per pound, so a 500 calorie a day gap is about a pound a week, and the pace slider runs from a quarter pound to 2 pounds a week. On the example, a moderately active TDEE of about 2,739 minus 500 gives a daily target of about 2,239, and the 15 pounds from 180 down to 165 takes about 15 weeks.
Two guardrails. It won't hand back a target under 1,200 calories a day for women or 1,500 for men, whatever pace you pick. And the timeline is labeled an estimate because the 3,500 figure loosens the longer a diet runs, which Hall showed in 2008. For the week counts at every common goal, see how long it takes to lose 10, 20, or 50 pounds.
What this number can't tell you
It can't tell you your number. Every formula was fit to a group, and individuals land a couple hundred calories either side of the group line. Here's how far off a TDEE calculator usually is.
It can't see the number move. Lose 20 pounds and there's less of you to run, so your burn drops, and a long diet trims the fidgeting too. The estimate from January is stale by April, and the calculator has no way to know.
It can't tell water from fat. Daily weight swings a couple of pounds on salt, carbs, and hydration alone, which is why the app judges a smoothed trend and never a single morning.
How do I calculate it myself?
How many calories should I eat a day?
To hold your weight, roughly your TDEE: BMR times an activity multiplier, the number this calculator gives you. To lose, eat under it by the gap the pace slider sets, never below 1,200 for women or 1,500 for men. The formula is a starting point. A few weeks of logging tells you how close it was.
How do I calculate my maintenance calories?
Estimate BMR from a formula, then multiply by an activity factor between 1.2 and 1.9. That's the calculator above. To measure it instead, log your weight and calories for two to three weeks, convert the weight trend to calories at 3,500 a pound, and subtract that from your average intake. HabitSync's observed mode does that math for you.
How do I calculate a calorie deficit?
Subtract your target intake from your maintenance calories. A 500 calorie gap works out to about a pound a week at 3,500 calories per pound. 250 is half a pound, 1,000 is two. Pick the pace on the slider and the calculator returns the daily target, with a floor of 1,200 calories for women and 1,500 for men.
What is my calorie maintenance?
The calories a day at which your weight holds steady. On paper it's your TDEE, and the calculator estimates it from your stats. In practice it's whatever your scale says it is, and the two can differ by a few hundred either way. Log both for a few weeks and the second number replaces the first.
Which formula, and how big a deficit?
Should I use Mifflin-St Jeor or Harris-Benedict?
Start with Mifflin-St Jeor. It was developed in 1990, it is the equation most dietitians reach for first, and it tends to be the most accurate from just height, weight, age, and sex. Harris-Benedict, first published in 1919 and revised in 1984, usually runs a little higher. Use it as a second opinion if your Mifflin number feels low.
When is Katch-McArdle the better formula?
Pick Katch-McArdle when you know your body fat percentage. It works from lean body mass instead of total weight, so it fits people who are leaner or more muscular than average, where the other two tend to underestimate. Without a body fat number the calculator falls back to Mifflin-St Jeor.
How accurate is a TDEE calculator?
Every formula here is a population average, so treat the result as a starting point, not a verdict. Your real maintenance calories can differ by a few hundred either way. The only way to know your own number is to track weight and intake for a few weeks and watch how your body responds.
What is a calorie deficit, and how big should it be?
A calorie deficit means eating below your TDEE. Roughly 3,500 calories sits in a pound, so about 500 fewer per day works out to a pound a week. This calculator lets you set a pace from 0.25 to 2 pounds per week, and it will not return a target below 1,200 calories for women or 1,500 for men.
Save this forecast
Run the numbers, then keep them. A free account carries your stats and target straight into the app, sets the calorie goal on your dashboard, and starts the 60 day projection from today. After a few weeks of weigh-ins, the projection stops trusting the formula and starts trusting you.
The math, and where it comes from
HabitSync did not invent any of these formulas. Here is each one, what it does in the app, and where to read about it.
Mifflin-St Jeor
The default formula, and the one most dietitians reach for first.
What it does here: Your BMR on the calculator, and the resting burn behind your dashboard forecast, whenever Mifflin-St Jeor is the formula selected in Profile. It is the default, so this is the one most accounts are using.
Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition. 1990;51(2):241-247.
The calculator uses the 1984 revision, not the 1918 original. Both are listed so you can compare them.
What it does here: The same two places as Mifflin-St Jeor, your calculator BMR and your dashboard resting burn, when you select Harris-Benedict in Profile.
Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition. 1984;40(1):168-182.
Harris JA, Benedict FG. A biometric study of human basal metabolism. Proceedings of the National Academy of Sciences. 1918;4(12):370-373.
Works from lean body mass, which is why it asks for body fat. The equation comes from the McArdle, Katch and Katch exercise physiology textbook and builds on Cunningham's finding that lean mass predicts resting metabolism better than total weight does.
What it does here: Your BMR on the calculator and your dashboard resting burn when you select Katch-McArdle and have entered a body fat percentage. Without one, the app quietly falls back to Mifflin-St Jeor rather than guessing at your lean mass.
McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Wolters Kluwer.
Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. The American Journal of Clinical Nutrition. 1980;33(11):2372-2374.
TDEE is BMR times an activity factor from 1.2 (sedentary) to 1.9 (athlete-level training). That physical activity level approach is the one the FAO, WHO and UN University laid out for estimating daily energy needs.
What it does here: Turns your BMR into TDEE, the calories out figure on the calculator and in your pace breakdown. Once your daily burn has been measured from your own logs, this stops being used on a paid account: that number comes from your logged weight and calories instead.
FAO/WHO/UNU. Human Energy Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. Rome; 2001.
The 3,500 calories per pound rule (7,700 per kilogram) is a simplification, and Hall's paper is why the timeline is labeled an estimate: the longer a diet runs, the less accurate that figure gets.
What it does here: Converts a calorie gap into weight per week. It sets the timeline on the calculator, the projected line on your weight forecast, and the weekly rate on the pace card. It is also how your daily burn gets worked backward from your weight trend.
Wishnofsky M. Caloric equivalents of gained or lost weight. The American Journal of Clinical Nutrition. 1958;6(5):542-546.
Hall KD. What is the required energy deficit per unit weight loss? International Journal of Obesity. 2008;32(3):573-576.
This calculator is for informational purposes only and isn't medical advice. Talk to a doctor or registered dietitian before making changes, especially if you have a medical condition or are pregnant. Calorie balance is the biggest lever for most people, but it isn't the only one: sleep, stress, hormones, medications, muscle mass, and water retention can all move the number on the scale independent of what you eat. Read the full medical disclaimer.