IIFYM Flexible Dieting: How to Calculate Your Macros
IIFYM, or "if it fits your macros", lets you eat any food as long as you hit your protein, carb and fat targets. Here is how to calculate yours in 5 steps.
What is IIFYM?
IIFYM stands for "if it fits your macros". Instead of banning foods or following a fixed menu, you set daily targets for protein, carbohydrates and fat, and you can eat any food that fits those numbers. It is a form of flexible dieting. The idea is that what matters most for body composition is your total calories and your protein, not whether a food is labelled good or bad.
This does not mean you should eat only treats. Most people who do well with IIFYM build about 80 percent of their diet from whole, nutritious foods and use the remaining 20 percent for foods they enjoy.
Step 1: Estimate your maintenance calories
Start with your resting burn using the Mifflin-St Jeor equation, then multiply by your activity level to get maintenance calories. The full method is in how to calculate your daily calorie needs, and what TDEE is explains the idea.
Step 2: Adjust for your goal
- To lose fat: eat about 15 to 25 percent below maintenance.
- To maintain: eat at maintenance.
- To build muscle: eat about 5 to 15 percent above maintenance. See how many calories to eat to build muscle.
Step 3: Set your protein
Protein comes first because it protects muscle and keeps you full. A common range is 1.6 to 2.2 grams per kilogram of body weight. Read how much protein athletes really need for the reasoning.
Step 4: Set your fat
Aim for about 0.7 to 1 gram of fat per kilogram of body weight, and not less than roughly 20 percent of your calories. Fat supports hormones and the absorption of some vitamins.
Step 5: Fill the rest with carbohydrates
Protein and carbohydrates provide 4 calories per gram and fat provides 9. Take your calorie target, subtract the calories from protein and fat, and divide what is left by 4 to get your carbohydrate grams.
A worked example
A woman weighing 65 kg wants to lose fat and her maintenance is about 2,100 calories.
- Target: 20 percent deficit = about 1,680 calories
- Protein: 2 g per kg = 130 g, which is 520 calories
- Fat: 0.8 g per kg = 52 g, which is 468 calories
- Carbohydrates: (1,680 - 520 - 468) / 4 = about 173 g
So her daily targets are about 1,680 calories, 130 g protein, 52 g fat and 173 g carbs. For a deeper look at the three macros, read understanding macronutrients, and for weight loss specifically, how to calculate your macros for weight loss.
How to use flexible dieting well
- Hit protein first, then fit everything else around it. Missing protein is the most costly miss.
- Allow a small range. Being within about 5 to 10 grams of each target is fine. Perfection is not needed.
- Do not ignore fibre and micronutrients. Aim for roughly 25 to 35 grams of fibre and plenty of vegetables and fruit, because calories alone do not make a diet healthy.
- Be accurate with portions. Flexible dieting only works if your tracking is honest. See how to track calories accurately.
- Look at weekly averages. Hitting your numbers across the week matters more than any one day.
Typical macro splits for common goals
Percentages are a handy way to picture a diet, though the gram based method above is more precise because it protects protein first. These are common ranges, not rules.
- Fat loss: about 30 to 35 percent protein, 25 to 35 percent fat, 30 to 45 percent carbohydrate.
- Maintenance: about 20 to 30 percent protein, 25 to 35 percent fat, 40 to 55 percent carbohydrate.
- Muscle gain: about 20 to 30 percent protein, 20 to 30 percent fat, 45 to 55 percent carbohydrate.
Endurance athletes usually need more carbohydrate, while someone who simply wants a comfortable diet may prefer a bit more fat. The best split is the one you can follow consistently and that meets your protein target.
Building a plate that fits your macros
Once you know your numbers, a plate is just a combination of foods from each group. For a meal around 500 calories with about 35 g of protein, you could pick:
- Protein: 120 g of chicken breast, a can of tuna, 3 eggs or 200 g of Greek yoghurt.
- Carbohydrate: 150 g of cooked rice, a medium potato or two slices of whole grain bread.
- Fat: a teaspoon of olive oil, a quarter of an avocado or a few nuts.
- Vegetables and fibre: as many as you like, since they add little energy.
Use the high protein foods list when you need ideas, and the balanced plate guide to keep meals nutritious.
Reading labels for macros
Packaged foods list protein, carbohydrate and fat per serving or per 100 g. Check which one you are reading, because serving sizes can be small. Two other details matter. Fibre is part of total carbohydrate but contributes fewer calories, and alcohol provides about 7 calories per gram without belonging to any macro group, so drinks must be counted separately. For a deeper guide, read reading a nutrition facts label correctly.
Flexible dieting when you eat out
Flexible dieting is easier than strict meal plans in restaurants. Look at the menu for a protein you can estimate, such as grilled chicken, fish or steak. Choose a side that fits your carbohydrate goal, and ask for sauces on the side. Log your best estimate with a buffer of about 10 to 20 percent. If the meal runs over your macros, balance it out lightly across the next day or two instead of trying to compensate immediately. See eating out without derailing your goals.
Frequently asked questions
Is IIFYM the same as counting calories? It builds on calorie counting. You still hit a calorie target, but you also set protein, carbohydrate and fat goals, which improves the quality of the diet.
Do I have to hit my macros exactly? No. A range of about 5 to 10 grams either side of each target is fine, and the weekly average matters more than any single day.
Is IIFYM healthy? It can be, if most of your food is nutritious and you meet fibre and micronutrient needs. If you eat only processed foods that fit your numbers, you may hit your macros but still feel poor.
What is the difference between IIFYM and keto? IIFYM places no limit on any food group and keeps carbohydrate flexible. Keto restricts carbohydrate heavily to push the body into ketosis.
Can I use IIFYM to gain muscle? Yes. Set a surplus of 5 to 15 percent above maintenance, keep protein high and train with weights. See how many calories to eat to build muscle.
Who should be careful
IIFYM relies on tracking food, which does not suit everyone. If counting makes you anxious or you have a history of disordered eating, choose a simpler approach and speak to a health professional. People with medical conditions, and anyone who is pregnant or breastfeeding, should get personal advice before setting macro targets.
This article is general information, not medical advice.
Common IIFYM mistakes
- Hitting macros with only processed food. You can match the numbers with pastries and protein bars, but you will likely feel hungry and low on energy. Keep most of your food whole and nutritious.
- Ignoring fibre. Fibre does not appear in the three macros, yet it affects fullness, digestion and long term health. Aim for 25 to 35 grams.
- Leaving protein to the end of the day. If you have 40 grams left at 9 pm, it is hard to reach. Plan protein into every meal.
- Never adjusting. Your targets should change as your weight, activity and goal change. Review them every few weeks.
- Obsessing over exact grams. Staying within a small range is enough. The aim is a flexible, sustainable diet, not a perfect spreadsheet.
How FiTPLATE helps with flexible dieting
- Macros calculated for you. Answer a few questions and FiTPLATE sets your daily calories, protein, carbs and fat from your own data.
- A daily log built around macros. Log foods by search, quick add or barcode, and see each macro fill up through the day.
- Meals that fit your numbers. Generate a meal from your ingredients or browse the Sports Kitchen, with the nutrition of every recipe already shown.
- Targets that adapt. Your weekly weigh-ins feed a review that suggests changes to your targets as your body changes.