How to use the calculator
- Enter your age (the tool works for ages 18 to 80).
- Pick your gender.
- Add your height and weight. You can switch between US units, metric, or other units.
- Choose your activity level. Be honest here, because this one setting changes your results a lot.
- Pick your goal: maintain, lose, or gain weight.
- Hit Calculate.
Not sure which activity level fits? Here's a simple way to think about it:
- Exercise means 15 to 30 minutes of activity that keeps your heart rate up.
- Intense exercise means 45 to 120 minutes.
- Very intense exercise means 2 hours or more.
A real example, step by step
Numbers make more sense with an example. Let's say someone is 25 years old, 180 cm tall (about 5'11"), and weighs 65 kg (about 143 lbs). They work out 4 to 5 times a week and just want to maintain their weight.
Using the Mifflin-St Jeor equation for a male, the resting calorie burn works out to roughly 1,655 calories a day. Multiply that by an activity factor of about 1.55 for a moderately active week, and you get around 2,565 calories a day.
Now let's split those calories. This example uses 50% carbs, 20% protein, and 30% fat:
| Macro | Share of calories | Calories | Grams per day |
|---|---|---|---|
| Carbs | 50% | about 1,283 | about 321 g |
| Protein | 20% | about 513 | about 128 g |
| Fat | 30% | about 770 | about 86 g |
*These figures are an illustration, not a prescription. Your own result will depend on your numbers, and different calculators use slightly different activity multipliers.*
Why carbs and fat matter so much
Protein gets all the attention, but carbs and fat make up the bulk of what you eat, so getting them right is where most of the progress happens.
Carbs: your body's quick fuel
Carbohydrates break down into glucose, which your brain and muscles love to use. Not all carbs are equal, though. Fruit, vegetables, beans, oats, and whole grains come with fiber and keep you full. Soda, candy, and a lot of packaged snacks digest fast and leave you hungry again soon after.
The common guideline is that carbs can make up roughly 45% to 65% of daily calories. If you train hard, you'll probably sit toward the higher end.
Fat: small amount, big job
Fat has a bad reputation it doesn't deserve. Your body needs it for hormones, for absorbing vitamins A, D, E, and K, and for building cells. It's also the most calorie-dense nutrient, which is why portions matter.
A typical range is 20% to 35% of daily calories. Most of that should come from foods like olive oil, nuts, seeds, avocado, and fish. US dietary guidance also suggests keeping saturated fat under 10% of your calories and avoiding trans fats where you can.
The math behind the results
You don't need to do this by hand, but it helps to know what's going on under the hood.
- Carbs: 4 calories per gram
- Protein: 4 calories per gram
- Fat: 9 calories per gram
So if your target is 2,000 calories and you want 30% from fat, that's 600 fat calories. Divide by 9 and you get about 67 grams of fat. Same idea works for carbs, just divide by 4.
The calculator estimates your calorie needs with two well-known formulas. Mifflin-St Jeor looks at your age, height, weight, and gender. Katch-McArdle also uses lean body mass, so it can be a better fit if you're lean and know your body fat percentage.
Tips to actually stick with your numbers
- Treat the result as a starting point. Follow it for two to three weeks, then check how your weight and energy are trending. Adjust by about 100 to 200 calories if needed.
- Don't chase perfection. Hitting your numbers within 5 to 10 grams is plenty close.
- Weigh food for a week or two. Eyeballing portions is the most common reason people feel stuck. After a short stretch, your eye gets much better.
- Look at your week, not just one day. A big dinner on Saturday doesn't undo five good days.
- Keep fiber up. Aim for plenty of vegetables, fruit, beans, and whole grains.
Quick macro numbers for common foods
| Food | Serving | Protein | Carbs | Fat |
|---|---|---|---|---|
| Egg | 1 large | 6.3 g | 0.4 g | 5 g |
| Rice | 1 cup cooked | 4.2 g | 44 g | 0.4 g |
| Banana | 1 medium | 1.9 g | 38.9 g | 0.6 g |
| Chicken, cooked | 2 oz | 16 g | 0 g | 1.8 g |
| Butter | 1 tbsp | 0.1 g | 0 g | 11.5 g |
| Milk (2%) | 1 cup | 8 g | 11.4 g | 4.8 g |
Values are approximate and vary by brand and cooking method.
Frequently asked questions
How many carbs should I eat a day?
It depends on your calorie needs and activity. A common range is 45% to 65% of your daily calories. On a 2,000-calorie day, that's about 225 to 325 grams.
How much fat do I need per day?
Most adults do well with 20% to 35% of calories from fat. On 2,000 calories, that's roughly 44 to 78 grams.
Is this calculator good for losing weight?
Yes. Choose "lose weight" as your goal and the calculator will lower your calorie target. Go slowly, because a very large calorie cut is hard to keep up and can leave you tired.
Do I need to count macros forever?
No. Many people track for a few weeks to learn what proper portions look like, then ease off and eat by feel.
Are these numbers exact?
No calculator can give exact numbers. These are estimates based on standard formulas. Your real needs can shift with sleep, stress, muscle mass, and health conditions.
Keep going: more free calculators
Once you know your carb and fat targets, these tools help you fill in the rest:
- Protein Calculator to find your daily protein goal
- Calorie Calculator for a closer look at your daily energy needs
- BMR Calculator to see what your body burns at rest
- Macro Calculator for the full macro breakdown
- BMI Calculator for a quick body-size check
A quick note on health
This calculator is for general information only and isn't medical advice. If you're pregnant, managing diabetes or another health condition, or recovering from an eating disorder, please talk to a doctor or registered dietitian before changing how you eat.