Calculator 01 · Daily intake
Calorie and macro calculator for athletes
Your calories come from a resting metabolic rate equation and your training load. Your protein and carbohydrate come from published position stands, and you can see exactly where your number falls inside each recommended range. Fat is what is left, which is honestly how it works.
How this calculator gets to your number
There are four steps, and every one of them is a place where a different reasonable assumption would give you a different answer. That is not a flaw in this calculator, it is the actual state of the science, and I would rather show you the joints than hand you a number that looks more certain than it is.
First it estimates your resting metabolic rate, which is roughly what you would burn if you spent the whole day lying still and awake. If you gave a body fat percentage, it uses the Cunningham equation, which works from fat-free mass alone: 500 plus 22 times your fat-free kilograms.[3] If you did not, it falls back to Mifflin–St Jeor, which uses weight, height, age and sex.[2]
Second, it multiplies that resting number by an activity factor tied to your training load, which gives a maintenance estimate. Third, it applies your goal: a twenty percent cut for fat loss, a ten percent bump for building. Fourth, it splits that total into grams. Protein is set per kilogram of bodyweight from the ISSN position stand, carbohydrate is set per kilogram from your training load, and fat gets whatever calories are left over with a floor at twenty percent of your intake.
Said the way I would say it out loud
Your body has a running cost just to exist. Training adds to it. We estimate the total, nudge it up or down depending on whether you are trying to gain or lose, and then decide how much of that food should be protein and how much should be carbs. Fat fills the gap. The number that comes out is a starting point for the next few weeks, not a law.
Why the equation switches when you give a body fat percentage
Mifflin–St Jeor is the default in almost every calculator on the internet, including the ones your doctor's office uses. It was validated in the general population, and in the general population it is good. In athletes it is a different story. A 2023 systematic review and meta-analysis pooled the studies comparing prediction equations against measured metabolic rate in athletes and found that Mifflin–St Jeor significantly underestimated resting metabolic rate, while the Cunningham equations, Harris–Benedict, De Lorenzo and Ten Haaf did not differ significantly from measured values.[1]
The reason is muscle. Fat-free mass is metabolically expensive and body fat is comparatively cheap, so two people at the same weight and height can have genuinely different resting burn rates. An equation that never asks about body composition cannot see that difference. An equation built on fat-free mass can. That is why the body fat field, optional as it is, changes the answer more than anything else on the form.
If you want a better body fat number, a DEXA scan runs somewhere around fifty to a hundred dollars at most sports medicine clinics and university labs, and a BodPod is similar. An InBody or a good smart scale is less accurate in absolute terms but perfectly serviceable for tracking change over time, which is usually what you actually care about.
Where the protein number comes from
The International Society of Sports Nutrition's position stand on protein concluded that 1.4 to 2.0 grams per kilogram of bodyweight per day is sufficient for most people who train.[4] The joint position of the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine lands in a similar place, at 1.2 to 2.0 grams per kilogram.[5]
This calculator sets you at 1.6 g/kg when you are maintaining, 1.8 when you are building and 2.0 when you are cutting. The cutting number is deliberately at the top of the range, because when calories come down, protein is what protects the muscle you spent all that time building. The evidence on higher protein during energy restriction is one of the more consistent findings in the whole field.
One caveat the calculator flags but cannot fully solve: grams per kilogram of total bodyweight overshoots for people carrying a lot of fat mass, because fat tissue does not need feeding with amino acids. If your body fat is above roughly thirty percent, a target based on fat-free mass or on a goal bodyweight is more sensible than one based on the number the scale shows today.
Where the carbohydrate number comes from
Carbohydrate is the macronutrient most likely to be under-eaten by people who train hard, and it is the one where the guidelines are most explicitly tied to how much work you are actually doing. The joint position statement gives daily targets by training load: three to five grams per kilogram for light activity, five to seven for about an hour a day, six to ten for one to three hours a day, and eight to twelve for four or more hours a day.[5]
The calculator aims for the middle of your band, then checks whether your calorie target can actually accommodate it after protein and a minimum fat intake are accounted for. When it cannot, you get a warning rather than a quietly shrunken number. That warning is often the most useful thing on the page. It usually means one of three things is true: the deficit is too aggressive, the training volume is more than the eating can support, or the training load selection is more ambitious than the training actually is.
Said the way I would say it out loud
Carbs are the fuel your hard sessions run on. The harder and longer you train, the more you need, and there is a point where cutting calories and training hard stop being compatible. If the tool tells you the numbers do not fit together, believe it. That is not a rounding error, that is your training and your eating pulling in opposite directions.
Why fat is the leftover
Fat is essential — for hormone production, for absorbing vitamins A, D, E and K, for cell membranes, for the simple fact that food with no fat in it is miserable to eat. What it is not is performance-limiting in the same direct way carbohydrate is. So the sensible order of operations is to set protein for tissue, set carbohydrate for fuel, and let fat take the remaining calories.
The floor matters though. The position statement recommends fat make up twenty to thirty-five percent of energy intake and specifically advises against dropping below twenty percent, because very low fat intakes are associated with problems absorbing fat-soluble vitamins and with disrupted sex hormone production.[5] This calculator holds that twenty percent floor and will squeeze carbohydrate before it squeezes fat past it.
Energy availability, which is the number I actually worry about
If you give a body fat percentage, you get one output that most calculators do not provide, and it is the one I would look at first. Energy availability is the energy left for everything your body does other than exercise, expressed per kilogram of fat-free mass. The arithmetic is your intake minus the energy your training burns, divided by your fat-free mass.
Roughly 45 kcal per kilogram of fat-free mass per day is the benchmark for a body with enough to work with. Below about 30 is where the research starts finding menstrual dysfunction, reduced bone mineral density, suppressed thyroid and metabolic hormones, impaired immunity and worse performance — the cluster now described as Relative Energy Deficiency in Sport.[6] That is not a small aesthetic trade-off, and it accumulates quietly.
Athletes reach low energy availability two ways. Some deliberately restrict. Many more get there by accident, by adding training volume without adding food. The second group is larger and rarely realises what is happening, because nothing feels dramatic on any given day. If this calculator flags you under 30, that is worth taking to a dietitian rather than troubleshooting alone.
What to actually do with the number
Take the target, eat close to it for two to three weeks, and pay attention to four things: bodyweight trend, session quality, sleep, and hunger. Weight is the noisiest of the four over short windows because of fluid shifts, glycogen and gut contents, so use a weekly average rather than any single morning. If the trend is going the way you want and training feels good, the estimate was fine. If your weight is flat and you wanted it moving, adjust by about ten percent and give it another two weeks.
What I would not do is re-run this calculator every few days hoping for a different answer, or chase decimal places on your macros. The equation has error bars of a couple hundred calories on any given person. Your own two-week response to a target is more informative than any prediction equation will ever be, which is the whole reason we start with an estimate and then adjust.
Common questions
Why is this giving me more calories than other calculators?
Most likely because you entered a body fat percentage, which switches the calculation to a fat-free-mass equation. Trained people usually carry more fat-free mass than the general-population equations expect, and those equations underestimate accordingly. If the difference is large, it is telling you something real about how much muscle you carry.
Which activity level should I pick?
Pick based on structured training only, and be honest about the average rather than your best week. A desk job with four gym sessions a week is "moderate", not "high". If you are between two, pick the lower one and adjust upward later — an underestimate shows up as easy weight loss you can correct in a fortnight, whereas an overestimate quietly stalls you for a month.
Do I need to hit my macros exactly?
No. Protein is the one worth being fairly consistent about because it is doing structural work and the daily total genuinely matters. Carbohydrate is worth getting close to on hard training days specifically. Fat can float. If you land within about ten percent of the targets most days, you have captured essentially all of the available benefit.
Can I lose fat and gain muscle at the same time?
Yes, in specific circumstances: if you are new to resistance training, returning after a layoff, or carrying a fair amount of body fat. It gets harder the more trained and the leaner you are, and it needs high protein and a modest deficit rather than an aggressive one. If you are in that group, choose fat loss here and expect the scale to move slowly while the mirror moves faster.
Why does the calculator ask about sex assigned at birth?
Only because Mifflin–St Jeor was published with a sex term in the equation, and using it any other way would be misrepresenting the equation. If you enter a body fat percentage, the calculator uses Cunningham instead, which is based purely on fat-free mass and has no sex term at all — for anyone whose body composition does not match what a sex-based equation assumes, that is the more accurate route.
Is the "3,500 calories per pound" rate of change accurate?
It is a reasonable short-term approximation and a poor long-term one. The rule assumes your metabolism does not respond to weight loss, and it does — as you get lighter you burn less, so real-world loss curves flatten out. Expect the first few weeks to track roughly and the pace to slow after that. Treat the figure as an order of magnitude, not a schedule.
Is this medical nutrition therapy?
No. This is general nutrition education, the same information I would give in a group talk. Medical nutrition therapy means individualised assessment and a care plan for a diagnosed condition, delivered by a dietitian licensed where you are. If you have a medical condition, are pregnant, have a history of disordered eating, or take medication that affects appetite or metabolism, work with someone who can see your whole picture.
Sources for this page
The full equations, with coefficients, live on the methods page alongside a plain description of how much error to expect. These are the primary sources behind the numbers above.
- O'Neill JER, et al. Accuracy of resting metabolic rate prediction equations in athletes: a systematic review with meta-analysis. Sports Medicine, 2023. PMID 37632665
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990;51(2):241–7.
- Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition, 1980;33(11):2372–4.
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. JISSN, 2017;14:20. Full text
- Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. JAND, 2016;116(3):501–528. PMID 26891166
- Mountjoy M, et al. International Olympic Committee consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023.