How to use the macro calculator
Start with the number you trust most. If you don't have a calorie target, the calculator estimates one from your body details with the Mifflin-St Jeor equation and an activity factor. If a dietitian, coach or your own tracking already gave you a number, choose Use my calorie target instead.
Then choose how to split those calories. The default sets protein by body weight, gives fat a fixed share and hands the rest to carbs. You can also pick a preset split or type your own percentages.
- Choose Estimate from body details or Use my calorie target.
- Enter weight, and for an estimate, your sex, age, height and activity level, in metric or imperial units.
- For an estimate, keep maintenance or pick 10% or 20% below, 5% or 10% above, or a custom change from -30% to +30%.
- Pick a split: protein by body weight, 20/50/30, 20/55/25, 30/40/30, or custom percentages that add up to 100.
- Set meals per day if you want a per-meal view, then press Calculate.
Worked example at 2,200 calories
Take a 75 kg adult with a 2,200-calorie target. At 1.4 g of protein per kg, protein is 105 g, or 420 calories. Fat at 30% is 660 calories, about 73 g. That leaves 1,120 calories for carbs, which is 280 g. Over four meals, that's about 26 g protein, 70 g carbs and 18 g fat each.
The same calories can be split many ways. The table shows how much the grams move when only the split changes.
| Split | Protein | Carbs | Fat |
|---|---|---|---|
| Protein by weight: 1.4 g/kg at 75 kg, 30% fat | 105 g (19.1%) | 280 g (50.9%) | 73 g (30%) |
| 20 / 50 / 30 | 110 g (20%) | 275 g (50%) | 73 g (30%) |
| Higher carb 20 / 55 / 25 | 110 g (20%) | 303 g (55%) | 61 g (25%) |
| Higher protein 30 / 40 / 30 | 165 g (30%) | 220 g (40%) | 73 g (30%) |
| Custom 25 / 45 / 30 | 138 g (25%) | 248 g (45%) | 73 g (30%) |
Macro calculator for women
The calculator asks for sex because Mifflin-St Jeor uses a different constant for men and women. At the same age, height and weight, the female estimate of resting calories comes out 166 calories lower. Protein is set from body weight, so it doesn't change with sex.
Here's a woman who is 35, 165 cm tall, 65 kg and lightly active. Her resting estimate is about 1,345 calories and her maintenance about 1,850. At 10% below maintenance she gets about 1,665 calories. With 1.4 g/kg protein and 30% fat, that's 91 g protein, 55 g fat and about 200 g carbs.
| Calorie setting | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| Maintenance | 1,850 | 91 g (19.7%) | 233 g (50.3%) | 62 g (30%) |
| 10% below | 1,665 | 91 g (21.9%) | 200 g (48.1%) | 55 g (30%) |
Macros for weight loss
Weight loss comes from the calorie side. The macro split mostly shapes how you get there. In estimate mode, pick 10% or 20% below maintenance, or set your own percentage. A visible percentage is easier to check than a hidden fixed cut: 10% below 2,200 is 220 calories.
Setting protein by body weight helps when calories drop. A fixed percentage shrinks your protein grams as calories fall, while a g/kg target keeps them steady and takes the cut from carbs. The calculator doesn't predict how fast you'll lose weight. NIH's Body Weight Planner uses a dynamic model for that question.
The macro formulas
Protein and carbs count as 4 calories per gram and fat as 9. The calculator keeps unrounded numbers inside and rounds only what you see, so the macro calories add back to your target.
Maintenance calories = Mifflin-St Jeor resting energy x activity factorAdjusted calories = maintenance x (1 + adjustment % / 100)Protein or carb grams = calories for that macro / 4Fat grams = fat calories / 9Protein by weight = body weight in kg x g/kg targetCarb calories = total calories - protein calories - fat calories
Reference ranges the results are checked against
Each result shows whether your split sits inside the adult Acceptable Macronutrient Distribution Ranges from the National Academies. Being outside a range is a reason to understand the tradeoff. It isn't a verdict on the plan. A 30/40/30 split, for example, puts carbs below 45%.
You'll also see a fiber reference of 14 g per 1,000 calories and a saturated fat ceiling of 10% of calories. Fiber is part of your carbs, so it isn't added on top.
| Reference | Protein | Carbs | Fat |
|---|---|---|---|
| National Academies AMDR | 10-35% of calories | 45-65% of calories | 20-35% of calories |
| National Academies RDA basis | 0.8 g/kg | 130 g/day | No total-fat RDA |
| Dietary Guidelines 2025-2030 | 1.2-1.6 g/kg/day serving goal | Favor fiber-rich whole foods | Saturated fat under 10% of calories |
When to get personal advice instead
Mifflin-St Jeor is a population equation and activity levels are broad, so treat your first number as a starting guess. A few weeks of steady tracking and weigh-ins tell you more than any formula. Day-to-day scale changes mostly reflect water, salt, glycogen and digestion.
This is an adult planning tool. It isn't designed for pregnancy or breastfeeding, kidney or liver disease, diabetes medication changes, prescribed diets or anyone under 18. If tracking food starts to feel stressful or rigid, stop and talk to a registered dietitian or doctor.
Sources
These references back up the energy equation, the macro ranges and protein references, and the note on how weight change works over time.