Macros are the three nutrients that carry calories: protein, carbohydrates, and fat. Counting them instead of just counting calories does one useful thing: it makes sure the calories you eat are doing the jobs you want them to do, like keeping muscle while you lose fat, or fueling training while you build. Setting your targets takes about ten minutes and four steps. Here is the whole process, with the math shown. If you would rather skip the arithmetic, our free macro calculator runs these exact steps for you.
Step 1: Estimate your maintenance calories
Maintenance is the intake at which your weight roughly holds steady. Everything else is measured from it, so start here.
First estimate your basal metabolic rate (BMR), which is what your body burns at rest. The Mifflin-St Jeor equation is the standard tool for this:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Then multiply BMR by an activity factor to account for everything you do beyond lying still:
| Activity level | What it looks like | Multiplier |
|---|---|---|
| Sedentary | Desk work, little exercise | 1.2 |
| Lightly active | 1 to 3 workouts a week | 1.375 |
| Moderately active | 3 to 5 workouts a week | 1.55 |
| Very active | 6 to 7 workouts a week | 1.725 |
| Extremely active | Hard daily training or a physical job | 1.9 |
Two caveats. These equations estimate the average person with your stats, and you are not average, so expect your true maintenance to sit somewhere near the number rather than exactly on it. And almost everyone overrates their activity level. If you lift four times a week but sit for work, you are moderately active, not very active. When in doubt, pick the lower tier; you can always add calories later.
Worked example
Alex is a 30-year-old man, 5'10" (178 cm), 180 lb (81.6 kg), lifting four days a week with a desk job.
BMR = 10 × 81.6 + 6.25 × 178 − 5 × 30 + 5 = about 1,780 calories.
Maintenance = 1,780 × 1.55 = about 2,760 calories a day. That is Alex's starting estimate, to be checked against real results.
Step 2: Adjust for your goal
Cutting
To lose fat you eat below maintenance. A moderate deficit of 10 to 20 percent works well for most people. It is large enough to make progress you can measure over weeks, and small enough that you can train, sleep, and think straight while you do it. Bigger deficits exist, but they get harder to sustain and make it easier to lose muscle along with fat, which defeats the point of counting macros in the first place.
Bulking
To build muscle you eat a little above maintenance, and "a little" is the key phrase. A surplus of 5 to 15 percent supports training and recovery. Muscle is built slowly no matter what you eat; a bigger surplus mostly builds a bigger cut for later.
Maintaining
Eating at maintenance is underrated. It is where you learn what consistent eating feels like, where you hold results after a cut, and where many people perform best in the gym. If you are new to tracking, a few weeks at maintenance is a genuinely good first goal.
Worked example, continued
Alex decides to cut. A 15 percent deficit is 2,760 × 0.85 = about 2,350 calories a day. His conservative range is roughly 2,210 to 2,480.
One thing you will not find here is a promise about how fast the scale will move. Rate of change depends on your body, your consistency, and things no calculator can see. Set the target, run it for a few weeks, and let your own results tell you whether to adjust.
Step 3: Split the calories into macros
Set protein first, because it does the most structural work: it preserves muscle in a deficit, supports growth in a surplus, and keeps you full either way. A common, well-supported range is 0.7 to 1 gram per pound of body weight (about 1.5 to 2.2 g per kg) for people who train. If you carry a lot of body fat, run that range on your goal weight rather than your current weight; per pound of total weight it overshoots.
Then set fat. Your body needs it for hormones and general health, so do not crush it to zero. Somewhere between 20 and 35 percent of total calories, or roughly 0.3 to 0.45 g per pound, suits most people.
Carbs get everything that is left. They are your training fuel, so if your workouts feel flat, carbs are usually the dial to turn up first.
For the arithmetic: protein and carbs carry about 4 calories per gram, and fat carries about 9.
Worked example, continued
Alex, cutting on 2,350 calories at 180 lb:
- Protein: 0.9 g/lb × 180 = 162 g, call it 160 g (640 calories)
- Fat: 30% of calories = 705 calories ÷ 9 = about 78 g
- Carbs: the remaining 1,005 calories ÷ 4 = about 250 g
So Alex's day is roughly 2,350 calories, 160 g protein, 250 g carbs, 78 g fat. Round numbers are fine. These are targets to land near, not lines to hit exactly.
Second worked example
Jess is a 34-year-old woman, 5'5" (165 cm), 140 lb (63.5 kg), lifting three days a week with an office job. She wants to build.
BMR = 10 × 63.5 + 6.25 × 165 − 5 × 34 − 161 = about 1,335 calories. Maintenance = 1,335 × 1.55 = about 2,070. A 10 percent surplus puts her at about 2,280 calories a day.
- Protein: 0.9 g/lb × 140 = 126 g, call it 125 g (500 calories)
- Fat: 30% of calories = 684 calories ÷ 9 = about 76 g
- Carbs: the remaining 1,096 calories ÷ 4 = about 275 g
So Jess's day is roughly 2,280 calories, 125 g protein, 275 g carbs, 76 g fat. Notice the shape: her protein is 35 g lower than Alex's because she weighs 40 lb less, while her carbs are higher because she is building, not cutting. Same four steps, different numbers.
What about percentage splits?
You will also see macros given as percentages, like 30 percent protein, 40 percent carbs, 30 percent fat. Percentages are convenient and they are how most apps, including Prepwell's calculator, present presets: balanced (30/40/30), higher protein (40/30/30), and keto-leaning (30/10/60) are common starting points. The gram-first method above is slightly better tuned to your body weight, but either gets you close enough to start. Pick one, check that the protein grams land in that 0.7 to 1 g per pound range, and move on. The choice of split matters far less than hitting whatever you chose most days.
How often should you recalculate?
Less often than you would think. Your maintenance shifts as your weight changes, but slowly. Rerun the numbers when your body weight has moved by about 5 to 10 pounds, when your training changes in a lasting way, or when a long cut or bulk ends and you are setting up the next phase. Between those moments, adjust with the small 100 to 200 calorie nudges described below instead of starting from scratch.
Step 4: Run it, watch it, adjust it
The calculator gets you to the starting line; your own data does the rest. Eat at your targets for two to three weeks, weigh yourself a few times a week under the same conditions, and look at the weekly average rather than any single day, because daily weight bounces around with water and food timing.
I am the cautionary tale here, in the direction nobody warns you about. Left to my own habits, I undereat. Not on purpose, and not dramatically, just a little under every day, and the gym tells me before the scale does: the lifts stall and I cannot work out why until I add up an ordinary day and find I am short. I have to eat larger portions deliberately to make progress, and the moment I stop tracking, I drift back under within a couple of weeks. For me, structure is not a personality trait. It is the only thing that keeps the plan from evaporating.
- Cutting and the trend is flat? Take 100 to 200 calories off, mostly from carbs or fat, and give it another two weeks.
- Bulking and gaining faster than expected? Trim the surplus by a similar amount.
- Trending the way you want? Change nothing. Boring is winning.
Small, patient adjustments beat dramatic overhauls every time, mostly because you will actually stick with them.
The mistakes that cost people the most
- Overestimating activity. The most common error, and it wipes out a cut without anyone noticing. Choose the honest multiplier.
- Treating estimates as exact. Every number in this process, from the equation to the label on your oatmeal, is an estimate. Chasing single-gram precision adds stress without adding results.
- Changing targets every few days. Weight noise is not feedback. Two to three weeks of trend is.
- Picking targets you cannot live with. The best macro plan is the one you can follow on a Tuesday in week six. If a 20 percent deficit makes you miserable, a 10 percent deficit you sustain will beat it.
Do the math once, then stop doing math
So: estimate maintenance, nudge it toward your goal, set protein, fat, and carbs, then adjust based on what actually happens. Run your own numbers with the free Prepwell macro calculator, and the harder daily question, "what do I actually cook to hit these numbers?", is the one Prepwell answers.
Frequently asked questions
How accurate is the Mifflin-St Jeor estimate?
It is an estimate of the average person with your stats, and real maintenance commonly lands within about 10 percent of it in either direction. Use it as a starting point, then adjust after two weeks based on what your weight actually does.
Should I set protein by body weight or by percentage?
By body weight. Percentages move with your calories, so a cut can leave protein too low. Set protein in grams first (0.7 to 1 g per pound, on your goal weight if you carry a lot of body fat), then set fat, and let carbs fill the rest.
How often should I recalculate my macros?
When your weight changes by about 5 to 10 pounds, or when your training or goal changes. Between those points, adjust by 100 to 200 calories based on the two-week trend rather than rerunning the formula.
Do I need to hit my macros exactly every day?
No. Land within about 5 to 10 grams of protein and 100 calories most days and the weekly average does the work. Treat targets as a range, not a line.