Step 1: settle on a calorie number
Every macro plan rests on a calorie target, so get that first. The most common estimate is Mifflin-St Jeor: 10 x weight in kg + 6.25 x height in cm - 5 x age, then +5 for men or -161 for women. Multiply by an activity factor from 1.2 (sedentary) to 1.9 (very active).
A 35-year-old woman at 165 cm and 65 kg gets 650 + 1,031.25 - 175 - 161 = 1,345 calories at rest. Lightly active (1.375) puts her near 1,850. Remember this is a population estimate. Your real needs show up in a few weeks of tracking.
Formula notes
Resting calories (men) = 10 x kg + 6.25 x cm - 5 x age + 5Resting calories (women) = 10 x kg + 6.25 x cm - 5 x age - 161Maintenance = resting calories x activity factor
Step 2: anchor protein to your body weight
Set protein in grams per kilogram before anything else. The National Academies base the adult RDA on 0.8 g/kg. The 2025-2030 Dietary Guidelines list 1.2 to 1.6 g/kg a day as a general goal. Pick a number in that range and multiply by your weight.
At 1.4 g/kg, the 65 kg woman needs 91 g. Multiply by 4 to get calories: 364. Doing protein first means it stays the same if you later cut calories. If she drops to 1,665 calories, protein stays at 91 g and the cut comes out of carbs and fat.
Step 3: pick a fat share, then fill in carbs
Give fat a percentage of calories. The adult reference range is 20% to 35%, and 30% is a common middle. Multiply your calories by that share and divide by 9, since fat has 9 calories per gram.
Carbs get whatever's left. Subtract protein and fat calories from your total and divide by 4. For the woman at 1,850 calories: fat is 555 calories, or about 62 g. Carbs get 1,850 - 364 - 555 = 931 calories, about 233 g.
- Calories: 1,850
- Protein: 91 g (364 calories)
- Fat: 62 g (555 calories)
- Carbs: 233 g (931 calories)
Step 4: check the result
Add it back up: 91 x 4 + 233 x 4 + 62 x 9 is 1,854, a few calories over because of rounding. That's close enough. Then check the percentages against the adult ranges: protein 10% to 35%, carbs 45% to 65%, fat 20% to 35%. This example lands at about 20/50/30.
If you'd rather skip the arithmetic, our macro calculator runs all four steps and flags any share outside those ranges.
Mistakes that throw the numbers off
Using percentages for protein on a low-calorie plan is the big one. At 1,400 calories, 20% protein is only 70 g, which may be less than you meant. Setting protein in g/kg avoids that.
A few other slips come up a lot. People pick an activity level from their best week instead of a typical one. They mix up pounds and kilograms. And they count fiber on top of carbs, when it's already part of them. And don't chase every daily swing on the scale. Water and salt move it more than fat does in the short run.
Frequently asked questions
How many calories are in a gram of each macro?
Protein and carbs have about 4 calories per gram and fat about 9. Alcohol has calories too, but it isn't one of the three macro targets.
Do I need to hit my macros exactly every day?
No. Being close on most days matters more than hitting every gram. Weekly averages are a fair way to judge how you're doing.
How often should I recalculate my macros?
Recalculate after a meaningful change in body weight or activity, or if several weeks of tracking show your weight moving differently than planned.
What's the difference between total carbs and net carbs?
Total carbs include fiber. Net carbs subtract fiber and sometimes sugar alcohols. Food labels and apps don't all count them the same way, so pick one method and stick to it.
References
These sources support the method or guidance used for Macro Calculator. Verify time-sensitive rules at the source.
Try the calculator
Open Macro Calculator, enter your scenario, and compare its supporting rows with this guide's method and checks.