What this calculator actually does
You give it a calorie number. It hands back three numbers: grams of protein, grams of carbs, grams of fat. That’s the whole job.
The math is simpler than most people assume. Protein and carbs each carry 4 calories per gram. Fat carries 9. So if your split says 30% of calories should come from protein and your target is 2,200 kcal, that’s 660 kcal from protein, divided by 4, which lands at 165 grams. Carbs and fat work the same way with their own percentages.
Don’t know your calorie number yet? Switch to the body-stats mode and the tool estimates it for you from your age, sex, weight, height, and how often you train. It runs the Mifflin-St Jeor formula to get a resting burn, multiplies by an activity factor, then adjusts for whether you’re cutting, holding, or bulking.
Picking a split
The preset splits cover most situations:
- Balanced (30/40/30) is the default. Fine for general training, recomp, or someone who just wants a sane baseline.
- High protein (40/35/25) suits anyone in a cut who wants to hold onto muscle. More protein keeps you fuller too.
- Low carb (35/20/45) drops carbs without going to extremes.
- Keto (25/5/70) pushes fat way up and carbs down to almost nothing. Only useful if you’re actually running keto.
Hit Custom and you can type your own percentages. They don’t even have to add up to exactly 100. If you enter 35/35/35, the calculator normalizes it back to 100% before working out grams, and it tells you it did that. Handy when you’re sketching a split in your head and the numbers don’t quite line up.
A quick reality check on the calorie estimate
The estimated calorie number is a population average, not a measurement of your specific metabolism. Two people with identical stats can burn 300 calories apart. So here’s the honest workflow: use the estimate to start, eat at that number for two weeks, weigh yourself a few times a week, and look at the trend. If the scale isn’t moving the way you want, adjust by 100 to 200 calories and reassess. The formula gets you in the ballpark. Your bathroom scale gets you the rest of the way.
One more thing: people tend to overrate their activity level. The gap between “moderately active” and “very active” is bigger than it feels. When in doubt, pick the lower tier.
Tips that save you trouble
Round your grams to something you can actually hit. Nobody weighs out 163.7 grams of protein. Treat the output as a target zone.
Protein is the macro to anchor first. Most lifters do well around 1.6 to 2.2 g per kilogram of bodyweight. In body-stats mode the tool shows you the g/kg figure right under the results so you can sanity-check whether your chosen split is giving you enough.
Carbs and fat are more flexible. Some people perform better with more carbs, others feel sharper on more fat. Once protein is locked, shuffle the other two to taste.
Frequently asked questions
Do I have to enter my body stats? Nope. If you already know your daily calorie target, switch to manual mode and just type it in. The body-stats fields disappear and you go straight to the split.
Why use 4/4/9 instead of more exact numbers? Those are the Atwater values nutrition labels are built on. Fat is technically closer to 9.4 and protein has a digestion cost, but 4/4/9 is the standard everyone tracks against, so your math will match your food labels.
My custom percentages don’t add to 100. Is that broken? No, it’s handled. The calculator scales whatever you enter back to 100% and shows a small note so the grams stay accurate.
Can I use this for keto or carnivore? Yep. Pick the keto preset for very low carbs, or go custom and set carbs near zero. The grams update instantly.
Is the calorie estimate safe for medical use? It’s a general estimate, not a prescription. If you have a medical condition or a history with disordered eating, work with a registered dietitian instead of an online tool.