π½οΈ IIFYM Calculator
Flexible dieting targets from your stats and goal.
For informational purposes only, not medical advice. Consult a healthcare professional.
IIFYM, short for If It Fits Your Macros, sets daily targets for protein, fat, and carbohydrates instead of banning foods. Hit the macro numbers and total calories, and the specific foods are up to you. It works because fat loss and muscle gain are driven by energy balance and protein intake far more than by any particular food list.
This calculator builds your targets in three steps: basal metabolic rate from the Mifflin-St Jeor equation, total daily expenditure from your activity level, then a goal adjustment of minus 20% for cutting or plus 10% for lean bulking. Protein is set per pound of body weight, fat gets a moderate share, and carbs take whatever calories remain.
How to Use This Calculator
Enter sex, age, height, and weight, then pick the activity level that honestly matches your week, including workouts. Choose your goal: lose fat, maintain, or build muscle. The calculator returns daily calories plus protein, fat, and carb grams. Weigh yourself a few times a week and adjust: if weight is not moving after two to three weeks, nudge calories by 100 to 200, not by overhauling everything.
Enter your stats and pick the activity level that matches a normal week.
Choose your goal: cutting, maintenance, or lean bulking.
Read your calorie target and the protein, fat, and carb grams.
Track food against the targets for 2 to 3 weeks, then adjust calories up or down by 100 to 200 based on the scale trend.
The Math Behind Your Macros
BMR (women) = same - 161
TDEE = BMR x activity (1.2 to 1.9)
The Mifflin-St Jeor equation is the most validated BMR formula for healthy adults, outperforming the older Harris-Benedict in most comparisons. Multiplying by an activity factor gives TDEE, your true daily burn. The goal adjustment is deliberately moderate: a 20% deficit typically yields 0.5 to 1% of body weight lost per week, fast enough to see progress and slow enough to keep muscle and sanity. Protein runs 0.8 to 1.0 grams per pound because the research consensus lands around 1.6 to 2.2 g/kg for retaining muscle in a deficit. Fat is set at 0.4 g per pound, enough for hormones without eating the carb budget. Carbs get the leftovers, which keeps training fueled.
Worked Example
A 30-year-old man, 178 cm and 82 kg, lightly active and cutting: BMR comes out near 1,788 cal, TDEE near 2,458 cal, and the 20% deficit lands at 1,966 cal per day. Protein is set at 181 g (1.0 g/lb) to protect muscle in the deficit, fat at 72 g, and carbs fill the rest at 148 g. Switch the goal to maintenance and the same stats give about 2,458 calories with protein at 0.8 g per pound.
How to Read Your Targets
Protein is the non-negotiable number: hit it daily and the diet keeps working even on imperfect days. Fat is a minimum for hormonal health, so treat it as a floor rather than a ceiling to chase. Carbs are the flexible lever; move them up on training days and down on rest days if you like, as long as the weekly average holds. Fiber matters more than most people expect: 25 to 35 grams a day keeps hunger down and digestion normal, which is half the battle on a cut.
| Goal | Calorie adjustment | Protein |
|---|---|---|
| Lose fat | TDEE minus 20% | 1.0 g/lb |
| Maintain | TDEE | 0.8 g/lb |
| Build muscle | TDEE plus 10% | 0.9 g/lb |
When Macros Are Not Enough
IIFYM handles the math of body composition, not medical nutrition therapy. Diabetes, kidney disease, pregnancy, eating disorder history, and some medications change the rules, so check with your doctor or a registered dietitian before running a deficit with those in play. Very low calorie targets (under about 1,200 for most women or 1,500 for most men) deserve professional supervision. For informational purposes only, not medical advice. Consult a healthcare professional.
Related tools: TDEE calorie calculator, protein intake calculator and net carbs calculator.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What does IIFYM stand for?
If It Fits Your Macros. The idea is that any food can fit a diet as long as your daily protein, fat, carbohydrate, and calorie totals land on target.
Is IIFYM just an excuse to eat junk?
It can be abused that way, but the math does not care about food purity. Most successful flexible dieters still eat mostly whole foods because 200 grams of protein and 30 grams of fiber are hard to hit on junk alone.
How much protein do I really need?
For active people, research converges around 1.6 to 2.2 grams per kilogram of body weight daily. This calculator uses 0.8 to 1.0 g per pound, which sits inside that range.
Should carbs or fat be lower when cutting?
Keep protein high and fat at least 0.3 to 0.4 g per pound for hormones, then cut from carbs first since they are the most flexible fuel. Very low fat diets tend to feel worse.
What if my weight stalls for two weeks?
Drop calories by 100 to 200 or add a little activity, then wait another two weeks. Plateaus of under two weeks are usually water and noise, not a broken metabolism.
Can I do IIFYM as a vegetarian?
Yes, with planning. Hit protein through dairy, eggs, soy, legumes, and powders if needed. Vegetarians often need more total protein because plant proteins digest less completely.
Do I need to hit macros exactly every day?
Weekly averages matter more than any single day. Landing within about 5 to 10 grams on protein and 10 percent on calories keeps results on track without obsession.
Is the Mifflin-St Jeor equation accurate?
It is the best-validated BMR formula for the general population, usually within 10 percent. Very muscular or very obese bodies deviate more, which is why the two-week adjustment rule exists.