How your macros are worked out
These are the sums the Liftprep app runs. Each step uses the example filled in above: a 24-year-old man, 178 cm and 82 kg, on his feet some of the day, lifting four times a week and losing fat steadily.
Step 1: what you burn at rest
The calculator uses the Mifflin-St Jeor equation. In a 2005 review of the common equations, it was the one most likely to land within 10% of a measured resting rate.
| Sum | |
|---|---|
| Men | (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 |
| Women | (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161 |
For the example: 820 + 1,112.5 − 120 + 5 = 1,817.5 kcal.
Step 2: your day outside the gym
Your resting figure is multiplied by how active your day is.
| Day to day | Multiply by |
|---|---|
| Desk job | 1.2 |
| On my feet some of the day | 1.375 |
| Active job | 1.55 |
| Physical job | 1.725 |
For the example: 1,817.5 × 1.375 = 2,499 kcal.
Step 3: your gym sessions
Each session adds 250 kcal, spread across the week. Training stays separate from your activity level because you know exactly how many sessions you do.
For the example: 4 × 250 ÷ 7 = 143 kcal a day. That brings maintenance to 2,642 kcal, which rounds to 2,640 kcal.
Step 4: your goal
| Goal | Change from maintenance |
|---|---|
| Lose fat, steadily | −20% |
| Lose fat, gently | −12% |
| Maintain | None |
| Build muscle, lean | +10% |
| Build muscle, standard | +15% |
For the example: 2,642 × 0.8 = 2,113, which rounds to 2,110 kcal a day.
Step 5: protein
Protein is set first, from your body weight: 2.2 g per kg when you are losing fat and 1.8 g per kg otherwise. A deficit makes your body more willing to use muscle for fuel, so the target goes up. How much protein you need covers the research.
For the example: 82 × 2.2 = 180 g, which is 720 kcal at 4 kcal a gram.
Step 6: fat
Fat is the higher of 0.8 g per kg of body weight or 25% of your calories.
For the example: 0.8 × 82 = 65.6 g, and 25% of 2,110 kcal is 58.6 g. The higher figure rounds to 66 g, which is 594 kcal at 9 kcal a gram.
Step 7: carbs
Carbs take whatever calories are left, because they fuel your training and protein and fat are already covered.
For the example: (2,110 − 720 − 594) ÷ 4 = 199 g.
| Daily target | Example |
|---|---|
| Calories | 2,110 kcal |
| Protein | 180 g |
| Carbs | 199 g |
| Fat | 66 g |
Where the calculator stops
Some inputs change the answer, or stop it, because a low target can do harm:
- Calories never go below 1,500 for men or 1,200 for women, or below 65% of what you burn, whichever is higher.
- If your BMI is under 18.5, you get a suggestion to speak to a GP or dietitian in place of a target.
- If what you burn is already at the safe minimum, it won't set a fat-loss target.
- It is for adults, so anyone under 18 is pointed to a GP or school nurse.
If protein and fat don't both fit, protein drops towards 1.6 g per kg and fat stays where it is.
What to do with your numbers
Treat them as a starting point, then let your weight correct them. Weigh in a few mornings a week and compare weekly averages, because a single morning can move by a kilo on water and food alone.
When cutting, aim to lose 0.5 to 1% of your body weight a week. If the weekly average hasn't moved for two weeks, the deficit is too small. How to cut without losing muscle goes through the rest, and the best high-protein foods at a UK supermarket helps you hit the protein. Building muscle? The bulking calorie calculator covers how big your surplus should be and how fast to gain.
Common questions
What are macros?
Macros are the three nutrients that supply your calories: protein and carbs at 4 kcal a gram, and fat at 9 kcal a gram.
How accurate is a macro calculator?
It gives an estimate, because two people with the same stats can burn different amounts. Eat to the target for two weeks, check your weekly average weight, then adjust.
How much protein do I need to build muscle?
Research on people who lift points to 1.6 to 2.2 g per kg of body weight a day. This calculator uses 1.8 g per kg when you are building or maintaining and 2.2 g per kg when you are losing fat.
Are macros different for men and women?
Two things change: the last number in the resting calorie sum (+5 for men, −161 for women) and the minimum calorie floor. The protein and fat rules are the same for both.
Can I use stone and pounds?
The calculator takes kg and cm. To convert, multiply stone by 6.35 and pounds by 0.45, so 13 stone is about 82.6 kg. Multiply feet by 30.5 and inches by 2.54, so 5 ft 10 is about 178 cm.
Does the calculator save what I type?
No. The sums run in your browser and your age, height and weight stay on your device. Our website statistics record only that the calculator was used, the goal picked and the calories shown. The privacy policy has the details.
Is it free?
Yes. You don't need an account or an email address to use it.
Sources
- Mifflin MD et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51: 241–247.
- Frankenfield D, Roth-Yousey L, Compher C (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association 105: 775–789.
- Morton RW et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine 52: 376–384.
- Helms ER, Aragon AA, Fitschen PJ (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition 11: 20.