Calorie Calculator

Start on Mifflin-St Jeor. It came out of a 1990 study of 498 adults, the Academy of Nutrition and Dietetics recommends it for routine use, and it lands within 10 percent of a measured resting rate for roughly 82 percent of healthy adults against about 69 percent for Harris-Benedict. Switch to Katch-McArdle only if you have a body fat percentage from a scan or calipers rather than a bathroom scale, because it works from lean mass and inherits every error in that figure. The revised Harris-Benedict is worth a look as a second opinion: it usually reads a little higher, and the gap between the two tabs tells you how much of your target is equation choice rather than biology.

Because those are the lowest intakes commonly regarded as safe without medical supervision, 1,200 kcal a day for women and 1,500 for men. WebMD describes the same boundary as a band, at least 1,200 to 1,500 for women and 1,500 to 1,800 for men, and Sutter Health advises nothing below 1,200 for anybody. Most calculators print an unsafe number anyway and put a disclaimer elsewhere on the page. This one pulls the target back up to the floor, marks the bar, and recalculates the weekly rate from the deficit that actually remains. If your maintenance level is low enough that a 500 calorie cut breaches the floor, the honest answer is a smaller deficit and more movement, not a smaller plate.

As a measure of stored energy, roughly yes, and the figure traces back to Max Wishnofsky in 1958. As a prediction of weight loss it is wrong, because it assumes your expenditure stays constant while your weight falls. It does not: both your resting rate and the cost of moving your body drop as you get lighter. The worked comparison usually quoted is a 200 pound man cutting 500 calories a day, who loses about 23 pounds in a year rather than the 52 the old rule promises. The weekly rates beside the bars on this page are calculated the old way because it is the standard everyone recognises, and they should be read as a ceiling for the first few weeks rather than a schedule.

Pick the tier that matches an average week rather than your best one, and if you are torn between two, take the lower. The step sizes make the reason obvious: on a resting burn of 1,700 kcal, moving from moderately active at 1.55 to very active at 1.725 adds about 300 calories a day, which is larger than a gentle deficit. Overstating your activity by one tier can therefore cancel your entire plan while looking like progress on paper. A useful anchor is that lightly active is pegged in the literature at roughly 4,000 steps or two miles of walking a day, so measure a normal week before you choose.

More than you need at maintenance. The International Society of Sports Nutrition puts 1.4 to 2.0 g per kg of body weight a day as sufficient for most exercising people, and reports that 2.3 to 3.1 g per kg may be needed to protect lean mass in resistance-trained people who are in a deficit. The higher protein split on this page pushes protein to 35 percent of calories, the top of the acceptable range for adults, which for an 80 kg person eating 2,759 calories works out at about 3 g per kg. The same body of work notes that leaner people should cut more gently, because a slower rate of loss preserves more lean mass.

Because the target was calculated for a body that no longer exists. Resting energy scales with body mass, so as weight comes off your resting burn falls, and a lighter body also costs less to move around. The deficit you set has been shrinking quietly the whole time. Re-enter your current weight and let the calculator rebuild the bars rather than cutting further from the original number, which is how people end up below the floor. If the scale has been flat for three weeks at a genuinely lower weight, that is the new maintenance level, and the choice is a fresh deficit from there or more daily movement.

Smaller than most people assume. A surplus of 200 to 300 calories a day is enough to supply the extra energy without piling on fat alongside the muscle, which is why the gentle gain bar sits at 250 rather than 500. The steady gain bar at 500 is there for people who are underweight or struggling to eat enough, not as a default. Muscle is built slowly, so the surplus has to be paired with resistance training and enough protein or the extra calories simply become fat. On the losing side the same logic applies in reverse: a 300 to 500 calorie deficit that produces roughly 0.3 to 0.7 percent of body weight a week is far more sustainable than a steep one.

Only if you did not already count it. The activity multiplier on this page bundles your training into maintenance, so if you selected moderately active on the strength of five sessions a week, those sessions are already inside the number and eating them back a second time doubles the credit. Add them separately only if you chose sedentary and then did something unusual. It is also worth knowing that structured exercise is a smaller slice than it feels: all physical activity combined accounts for 15 to 30 percent of what you burn, and much of that is non-exercise movement, walking, standing and fidgeting rather than the gym.

No. Two of the three tabs, Mifflin-St Jeor and the revised Harris-Benedict, need only height, weight, age and sex at birth, and the body fat field stays out of the way until you open the Katch-McArdle tab. Katch-McArdle is the only one that asks for it, because it calculates lean mass as weight multiplied by one minus your body fat fraction and then applies 370 plus 21.6 per kilogram of that lean mass. Fed a measured figure it reads people with unusual body composition better than the other two. Fed a guess it is worse than either, so if you are estimating, stay on the first tab.

The equations say yes, and they quantify it. Mifflin-St Jeor subtracts 5 calories a day for every year of age, so all else being equal a 50 year old is credited with 100 fewer resting calories than a 30 year old of identical height and weight. The revised Harris-Benedict subtracts 5.677 a year for men and 4.330 for women. Part of that reflects lean mass lost over the decades rather than age itself, which is why Katch-McArdle drops the age term entirely and looks at lean mass directly. The practical point is that the age penalty in these equations is modest, around 100 to 170 calories across two decades, and it is comfortably inside the error band of the estimate.