Macros Calculator – From BMR Formulas To Daily Protein, Carbs And Fat
A macros calculator translates your calorie needs into a daily breakdown of protein, carbohydrates and fat. Instead of guessing portions, you work with numbers grounded in physiology: basal metabolic rate (BMR), total daily energy expenditure (TDEE), goal-based adjustments and macronutrient energy values. This Macros Calculator on MyTimeCalculator supports both metric and imperial units and multiple macro methods, from standard macros to athlete macros and IIFYM-style custom ratios.
Step 1: Basal Metabolic Rate (BMR) Formulas
BMR is the number of calories your body would burn in 24 hours at complete rest. The calculator uses two main BMR formulas and also mentions a classic alternative.
Mifflin–St Jeor BMR
This formula is widely used for general population estimates and underpins the standard macros tab. Weight is in kilograms, height in centimeters and age in years.
- For men: BMR = 10·weight + 6.25·height − 5·age + 5
- For women: BMR = 10·weight + 6.25·height − 5·age − 161
Harris–Benedict BMR (original version)
This is an older but still cited formula. Weight is in kilograms, height in centimeters and age in years.
- For men: BMR = 66.5 + 13.75·weight + 5.003·height − 6.755·age
- For women: BMR = 655.1 + 9.563·weight + 1.850·height − 4.676·age
Many modern calculators prefer Mifflin–St Jeor because it tends to match measured BMR more closely in typical adults.
Katch–McArdle BMR (lean body mass based)
For athletes and lifters, lean mass can be more informative than total body weight. The athlete tab uses Katch–McArdle, which depends on lean body mass (LBM) in kilograms.
- First compute LBM from body fat percentage:
LBM = weight · (1 − body_fat% / 100) - Then compute BMR:
BMR = 370 + 21.6·LBM
Because LBM excludes fat mass, this formula tends to give more goal-relevant BMR estimates for people with higher muscle mass.
Step 2: TDEE – Activity-Adjusted Calories
Once BMR is known, the total daily energy expenditure TDEE is approximated by multiplying BMR by an activity factor:
- Sedentary: TDEE ≈ BMR × 1.2
- Lightly active: TDEE ≈ BMR × 1.375
- Moderately active: TDEE ≈ BMR × 1.55
- Very active: TDEE ≈ BMR × 1.725
- Extra active: TDEE ≈ BMR × 1.9
In the calculator you choose your activity level, and the tool computes TDEE from your selected BMR formula.
Step 3: Goal-Based Calorie Targets
After approximating TDEE, the next step is to align calories with your goal: fat loss, maintenance, recomposition or muscle gain. A common approach is to use a percentage deficit or surplus relative to TDEE:
- Cutting (fat loss): Calorie target ≈ TDEE × (1 − deficit%)
- Bulking (muscle gain): Calorie target ≈ TDEE × (1 + surplus%)
- Recomposition: Calorie target near TDEE with modest adjustments
For example, if TDEE is 2 400 kcal and you choose a moderate 20% cutting deficit, the target is about 1 920 kcal per day. In the goal-based tab the calculator maps mild, moderate and aggressive levels to reasonable deficit and surplus percentages for each mode.
Step 4: Converting Calories To Macro Grams
The key idea of macros is that calories are divided between protein, carbohydrates and fat. Each macro has a defined energy content:
- Protein: 4 kcal per gram
- Carbohydrates: 4 kcal per gram
- Fat: 9 kcal per gram
If P%, C% and F% denote the macro percentages and Ctotal is total daily calories, then:
- Protein calories = Ctotal · P% / 100
- Carb calories = Ctotal · C% / 100
- Fat calories = Ctotal · F% / 100
Convert calories to grams using the energy values above:
- Protein grams = Protein calories ÷ 4
- Carb grams = Carb calories ÷ 4
- Fat grams = Fat calories ÷ 9
The standard, athlete, IIFYM and goal tabs all rely on these core relationships. When your macro percentages do not sum exactly to 100%, the calculator normalizes them to ensure the split is consistent.
Standard Macros: Mifflin–St Jeor And Macro Presets
The standard macros tab uses the Mifflin–St Jeor formula with your sex, age, height and weight. After converting imperial units (pounds and feet/inches) to metric equivalents, it computes BMR, multiplies by the chosen activity factor for TDEE and then applies a goal-based adjustment.
- Weight in kilograms from pounds: weight_kg = weight_lb · 0.45359237
- Height in centimeters from feet/inches: height_cm = (feet · 12 + inches) · 2.54
Macro presets such as 30% protein, 40% carbs and 30% fats are applied to the calorie target and converted to grams. If you pick the custom option, you can explicitly specify P%, C% and F% for your plan.
Athlete Macros: Lean Body Mass And Katch–McArdle
The athlete tab is tailored to lifters and athletes who know their body fat percentage. Using body fat percentage, the calculator first estimates lean body mass:
- LBM = weight · (1 − body_fat% / 100)
LBM feeds into the Katch–McArdle BMR formula:
- BMR = 370 + 21.6·LBM
An activity factor produces TDEE, and then goal-based adjustments are applied. Protein is often set first based on body weight or lean mass (for example about 1.8–2.2 grams per kilogram of body weight). Carbs and fats are then allocated from the remaining calories according to the goal, with cutting plans generally favoring slightly lower carbs and recomposition or bulking plans allowing higher carbs.
IIFYM Custom Macros: Any Percentages You Like
The IIFYM custom macros tab lets you choose your own standard for protein, carbs and fat percentages. The only requirement is that all percentages are non-negative and at least one is positive. The calculator then normalizes your chosen values so that the final split sums to 100%:
- P%norm = P% / (P% + C% + F%) · 100
- C%norm = C% / (P% + C% + F%) · 100
- F%norm = F% / (P% + C% + F%) · 100
Those normalized percentages are then used in the usual calorie-to-grams formulas. This makes it easy to set, for example, high-carb training days or higher-fat rest days if you manually adjust your target calories.
Goal-Based Modes: Cutting, Bulking And Recomposition
The goal-based tab focuses on what happens when you start with a known TDEE. You choose a mode and intensity and the calculator applies an appropriate multiplier:
- Cutting mild: calorie target ≈ TDEE × 0.9
- Cutting moderate: calorie target ≈ TDEE × 0.8
- Cutting aggressive: calorie target ≈ TDEE × 0.75
- Recomp mild: calorie target ≈ TDEE × 0.95
- Recomp moderate: calorie target ≈ TDEE × 1.0
- Recomp aggressive: calorie target ≈ TDEE × 1.05
- Bulking mild: calorie target ≈ TDEE × 1.05
- Bulking moderate: calorie target ≈ TDEE × 1.1
- Bulking aggressive: calorie target ≈ TDEE × 1.15
After this step, your macro percentages are applied to translate the target calories into grams. This separates the question “how aggressive should my deficit or surplus be?” from “how do I want to allocate calories among protein, carbs and fat?”
Weekly Macro Plan: Extending Daily Macros Across Seven Days
Once you are comfortable with daily macros, it is helpful to think in weekly terms. The weekly macro plan tab takes a single set of daily calories and macro grams and replicates them across the seven days of the week:
- Weekly calories = 7 · daily_calories
- Weekly protein grams = 7 · daily_protein_grams
- Weekly carb grams = 7 · daily_carb_grams
- Weekly fat grams = 7 · daily_fat_grams
Seeing a weekly total makes it easier to plan shopping, batch cooking and macro-friendly meal prep. You can also adapt the numbers if you prefer macro cycling, for example by manually increasing calories and carbs on certain days while reducing them on others.
How To Use This Macros Calculator Effectively
- Use the standard tab if you want a simple, evidence-based starting point based on Mifflin–St Jeor.
- Use the athlete tab if you know your body fat percentage and care about lean mass and performance.
- Use the IIFYM tab when you already have a calorie target and want full control over macro percentages.
- Use the goal tab if a coach or tracker has already estimated your TDEE and you want to explore different deficit or surplus levels.
- Use the weekly plan tab to translate daily macros into a bigger-picture view for seven-day planning.
The equations and values in this tool are standard in sports nutrition and fitness planning, but they are still approximations. Individual responses to calorie and macro changes vary with genetics, training, sleep, stress and health status. Treat the numbers as a structured starting point and adjust over time based on real-world feedback and, when appropriate, professional guidance.
Macros & Nutrition FAQs
Frequently Asked Questions About Macros
Quick answers to help you interpret macro numbers, calorie targets and the formulas behind this macros calculator.
No. Macros are targets, not strict rules. Being close most days is usually enough for practical progress. Many people think in weekly averages, which the weekly macro tab supports, so minor day-to-day variation is acceptable as long as your overall pattern fits your goals.
Practical ranges often fall between about 1.6 and 2.2 grams of protein per kilogram of body weight per day for active lifters. Higher protein intakes support muscle retention during cutting and muscle gain during bulking, while also helping with satiety. The athlete macros tab leans toward these higher ranges.
Both can work as long as protein and total calories are appropriate. Higher carb splits often suit people doing intense or high-volume training, while higher fat splits can feel more sustainable for lower-carb preferences. The IIFYM and goal-based tabs let you experiment with different splits while keeping calories constant.
Many people reassess macros every few weeks based on changes in body weight, performance, hunger and adherence. Rapid changes may justify slightly larger calorie adjustments, while slower, more stable progress often fits smaller, gradual changes in calorie or macro allocations.
If you have health conditions, especially those affecting metabolism, digestion or hormone balance, talk to a qualified healthcare professional before making major changes to diet or training. The calculator does not replace individualized medical or nutrition advice.