Protein4 kcal / g
1.6 – 2.2 g / kg
Rebuilds and preserves muscle. Aim for the high end during a cutting phase or if you're a beginner trying to put on muscle quickly.
Blog · Nutrition
How to calculate macros for muscle gain. The beginner guide.
May 15, 20268 min readBy ZymFit
Wondering where to start when it comes to calculating your macros? You're right to ask. Counting calories blindly without looking at what they're made of skips half the work. Macronutrients — protein, carbs, fats — largely decide your body composition and your performance in the gym.
This guide is intentionally minimal. We lay out the four-step method, walk through the useful ranges, and show how ZymFit runs the math for you while leaving you in control. No 30-day transformation promises, just a reliable framework to get started the right way.
01 / The right angle
Why calculate macros instead of just counting calories
Calories tell you how much you eat. Macros tell you what. For a physique or performance goal, the what changes everything. Two days at 2,200 kcal can send you in opposite directions: 80 g of protein and 350 g of carbs doesn't preserve muscle the same way as 160 g of protein and 220 g of carbs.
In strength training, three levers matter: a calorie intake aligned with your goal, enough protein to preserve or build muscle, and enough carbs and fats to support training and hormones. Everything else is a secondary detail.
Counting strictly to the calorie isn't essential. Hitting the right ranges of macros, over time, matters more. That's the angle we take in this guide.
02Formula
The base formula: BMR then TDEE
BMR (Basal Metabolic Rate) is the energy your body burns just to function at rest. The most cited formula is Mifflin-St Jeor:
Mifflin-St Jeor
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age
Then add +5 for men, −161 for women.
Once you have your BMR, you get your TDEE (Total Daily Energy Expenditure) by multiplying by an activity factor:
- 1.2 — sedentary, little or no activity
- 1.375 — 1 to 3 sessions per week
- 1.55 — 3 to 5 sessions per week (most common)
- 1.725 — 6 to 7 intense sessions
- 1.9 — physical job + daily training
Example: 165 lb (75 kg), 5'10" (178 cm), 28 years old, male, 4 sessions per week. BMR ≈ 1,700 kcal. TDEE ≈ 1,700 × 1.55 ≈ 2,635 kcal. That's your reference point, not an absolute truth: 2 to 3 weeks of tracking will refine the number.
03 / Split
How much protein, carbs, fats
The simple rule: set protein first, then fats, and let carbs close the equation. That's more reliable than starting from some 40/30/30 ratio pulled off a forum.
Fats9 kcal / g
0.9 – 1.4 g / kg
Essential for hormones and vitamin absorption. Don't drop below 0.8 g/kg long-term, even on an aggressive cut.
Carbs4 kcal / g
The rest
The fuel for your training. Calculate them by subtracting protein and fat calories from your total, then divide by 4.
Back to the example: 75 kg (165 lb), TDEE 2,635 kcal, maintenance goal. Protein at 1.8 g/kg ≈ 135 g (540 kcal). Fats at 1 g/kg ≈ 75 g (675 kcal). That leaves 2,635 − 540 − 675 = 1,420 kcal of carbs, or about 355 g per day.
If you want to go deeper on protein, we break down the approach in our piece on preserving muscle during a cutting phase.
04 / Goal
Adjust based on your goal
Three main roads from your TDEE. Pick one at a time, and hold it for a few weeks before adjusting.
Cutting
TDEE − 300 to 500 kcal
A moderate deficit to lose fat while limiting muscle loss. Keep protein at the high end of the range. To go further, read how to set the right deficit for sustainable weight loss.
Go deeperMaintenance
≈ TDEE
Ideal between phases, for stabilizing and working on body recomposition. Eat around your TDEE for 4 to 8 weeks and check the scale and the mirror.
Muscle gain
TDEE + 200 to 400 kcal
A controlled surplus to build muscle without stacking fat. ZymFit defaults to +400 kcal. We break down the method to calculate your surplus for a clean lean bulk.
Go deeper05In the app
How ZymFit calculates for you (and hands the wheel back)
During onboarding, you enter your age, sex, height, weight, activity level, and goal. ZymFit calculates your BMR with Mifflin-St Jeor, derives your TDEE, and suggests a calorie target: +400 kcal for muscle gain, around TDEE for maintenance, or a moderate deficit for cutting.
The default macro split: protein at 1.8 g/kg, fats around 1 g/kg, and carbs as the adjustment variable. But nothing is fixed: you can manually edit target calories and the grams of each macro in settings, anytime.
For logging, you get three entry points: AI photo scan, barcode scan, and manual search. The photo scan is the fastest way to scan your meals to log macros without tedious data entry.
06 / Real world
Adjust based on real results
No calculator nails the right number on the first try. Your real TDEE shows up in your data. The honest method: run your plan for 2 to 3 weeks, then look at your weight trend and how your training feels.
Three simple scenarios. Weight stable when you were targeting a cut? Cut another 100 to 150 kcal of carbs. Weight dropping too fast (more than 1% per week)? Add 100 to 200 kcal back to preserve your strength. Putting on fat too fast in a surplus? Drop back to +200 kcal instead of +400.
The scale lies day to day, not week to week. Smooth your weigh-ins over 7 days rather than reacting to a single number. And if you're new to lifting, take a look at how to structure your sessions with a beginner strength training program: without structured training, calculating macros to the gram won't get you very far.
FAQ
The questions we get asked most
What is TDEE?
TDEE (Total Daily Energy Expenditure) is the estimated number of calories your body burns over 24 hours, factoring in your basal metabolic rate and your activity level. It's the reference point you use to decide whether to eat in a calorie deficit, at maintenance, or in a surplus.
What's the best formula to calculate BMR?
Mifflin-St Jeor is the most widely used formula because it's simple and reasonably accurate for most people. It's still an estimate: the real number gets dialed in by tracking your weight trend over 2 to 3 weeks.
How much protein do you need for muscle gain?
A range of 1.6 to 2.2 grams of protein per kilogram of body weight per day covers strength training needs well. During a cutting phase, aim for the upper end of the range to better preserve muscle.
Do you really need to track every day?
Not forever. Tracking daily for a few weeks calibrates your eye and teaches you what real portions look like. After that, many lifters alternate strict tracking phases with looser ones while keeping protein as the non-negotiable.
Does ZymFit calculate macros automatically?
Yes. ZymFit estimates your TDEE from your profile and suggests a calorie target tuned to your goal — for example, +400 kcal above TDEE for a clean muscle gain phase. You can override calories and macros manually anytime in settings.
Read next
Three reads to take it one step further.
Training
Beginner strength training program: where to start
The framework for a solid first routine: frequency, key exercises, loading, progression. Without overloading your week.
Tracking
Weight tracking: read the real trend, not the noise
How to smooth your weigh-ins to see the actual direction rather than the water, salt, and digestion fluctuations.
Method
RPE in strength training: dialing in intensity without guessing
Rate of Perceived Exertion explained simply, to pilot your loads without basing everything on a theoretical 1RM.
Ready to try it
Let ZymFit do the math. You stay in control.
BMR, TDEE, macros, goal-based adjustments. It's all in the app, and you can override everything by hand if you prefer.