🥩 Macro & Calorie Deficit Calculator
Daily protein, carb and fat targets from the Mifflin-St Jeor equation — and the only calculator that checks your split against the official IOM ranges.
How this split compares with the official ranges
| Macronutrient | Your split | Official range (adults 19+) | Verdict |
|---|---|---|---|
| Protein | 30% | 10–35% | Within range |
| Carbohydrate | 40% | 45–65% | Below the range |
| Fat | 30% | 20–35% | Within range |
1 of 3 macronutrients fall outside the Institute of Medicine's Acceptable Macronutrient Distribution Ranges. That is not automatically wrong — low-carbohydrate and ketogenic diets are deliberately outside them — but it is worth knowing you have left the range the official guidance covers.
A meta-analysis of 49 trials covering 1,863 people found that protein intakes beyond about 1.62 g/kg/day produced no further gains in fat-free mass from resistance training. The popular “one gram per pound” rule works out at roughly 2.2 g/kg — well past that point. Extra protein is not harmful for healthy kidneys, but it is calories that could have gone elsewhere.
Calculated in your browser. Nothing is stored or sent anywhere, and there is no sign-up.
What Macro & Calorie Deficit Calculator Does
Nearly every macro calculator on the first page of Google runs the same arithmetic. It estimates your resting energy expenditure with the Mifflin-St Jeor equation, multiplies by an activity factor, adds or subtracts a few hundred calories for your goal, then slices the result into percentages and divides by 4, 4 and 9. The differences between them are almost entirely presentational.
What separates them is what they want from you. This particular search result is unusually commercial: meal-delivery companies, supplement brands and coaching services occupy most of page one, and several will not show your numbers until you hand over an email address. The calculation itself is not proprietary and never has been.
Since the arithmetic is common property, the useful thing a page can add is context on where those numbers come from and how much confidence they deserve. Two pieces of that context are missing from every competing page: whether your chosen split falls inside the ranges official dietary guidance actually covers, and the point at which more protein stops doing anything measurable.
The honest summary is that the calorie figure is a hypothesis, not a measurement. The equation behind it explains about 71% of the variation between people, and the activity multiplier you select moves the answer more than the equation does. Use the output as a starting point and let two or three weeks of real weight data correct it.
How to Use Macro & Calorie Deficit Calculator
- Choose Metric (kg/cm) or Imperial (lbs/in) units and select biological gender
- Enter your age, weight, height, and weekly activity level
- Select your goal (Fat Loss, Maintenance, or Muscle Gain)
- Choose a macro distribution preset (Balanced, High-Protein, Low-Carb, Keto)
- View your total daily calories, grams of protein/carbs/fat, and per-meal portions
Formula Used by Macro & Calorie Deficit Calculator
Mifflin-St Jeor equation — resting energy expenditure
Men: REE = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 · Women: REE = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
- REE
- Resting energy expenditure — calories burned at complete rest, per day
- weight
- Body weight in kilograms
- height
- Height in centimeters
Worked example
A 28-year-old man, 75 kg, 178 cm, moderately active (×1.55), aiming for fat loss
- 10 × 75 = 750
- 6.25 × 178 = 1,112.5
- 5 × 28 = 140
- REE = 750 + 1,112.5 − 140 + 5 = 1,727.5 kcal (shown as 1,728)
- Daily expenditure = 1,727.5 × 1.55 = 2,677.6 kcal
- Fat-loss target = 2,678 − 500
Result: 2,178 kcal a day — from which the macro split is then taken
Converting percentages to grams (Atwater factors)
grams = (calories × percentage) ÷ energy per gram, where protein = 4, carbohydrate = 4, fat = 9 kcal/g
- percentage
- Share of total calories assigned to that macronutrient
- energy per gram
- Atwater factor — an average, not an exact constant
Worked example
2,178 kcal split 20% protein, 50% carbohydrate, 30% fat
- Protein: 2,178 × 0.20 = 436 kcal ÷ 4 = 109 g
- Carbohydrate: 2,178 × 0.50 = 1,089 kcal ÷ 4 = 272 g
- Fat: 2,178 × 0.30 = 653 kcal ÷ 9 = 73 g
Result: 109 g protein, 272 g carbohydrate, 73 g fat — and at 75 kg that protein figure is 1.45 g/kg
Acceptable Macronutrient Distribution Ranges
Percentage of total energy intake. Set by the Institute of Medicine and used as the basis for US dietary guidance. Note how much wider the adult protein band is than most calculators imply.
| Macronutrient | Children 1–3 | Children 4–18 | Adults 19+ |
|---|---|---|---|
| Carbohydrate | 45–65% | 45–65% | 45–65% |
| Fat | 30–40% | 25–35% | 20–35% |
| Protein | 5–20% | 10–30% | 10–35% |
| n-6 polyunsaturated (linoleic acid) | 5–10% | 5–10% | 5–10% |
| n-3 polyunsaturated (α-linolenic acid) | 0.6–1.2% | 0.6–1.2% | 0.6–1.2% |
Source: Institute of Medicine — Dietary Reference Intakes, Acceptable Macronutrient Distribution Ranges
Common macro splits against the official adult ranges
Adults 19+. "Outside" is not a verdict on whether a diet works — low-carbohydrate approaches are deliberately outside the ranges — only a note that you have left the band official guidance covers.
| Split (protein / carbs / fat) | Protein 10–35% | Carbs 45–65% | Fat 20–35% |
|---|---|---|---|
| 20 / 50 / 30 — within official ranges | Within | Within | Within |
| 30 / 40 / 30 — commonly called "balanced" | Within | Below range | Within |
| 40 / 40 / 20 — the "40-40-20 rule" | Above range | Below range | Within (at the floor) |
| 40 / 35 / 25 — high protein | Above range | Below range | Within |
| 35 / 20 / 45 — low carb | Within | Below range | Above range |
| 25 / 5 / 70 — ketogenic | Within | Below range | Above range |
What each split means for protein per kilogram
A 75 kg person on a 2,178 kcal target. The right-hand column compares against the 1.62 g/kg point beyond which added protein produced no further gain in fat-free mass.
| Split | Protein | Per kg bodyweight | Versus the plateau |
|---|---|---|---|
| 20 / 50 / 30 | 109 g | 1.45 g/kg | Below |
| 30 / 40 / 30 | 163 g | 2.17 g/kg | Above |
| 35 / 20 / 45 | 191 g | 2.55 g/kg | Above |
| 40 / 35 / 25 | 218 g | 2.91 g/kg | Above |
| "One gram per pound" rule | 165 g | 2.20 g/kg | Above |
How to Read Your Result
The activity multiplier is where the error lives
People agonize over which BMR equation to use when the choice barely matters — the common ones land within a hundred calories of each other. The activity multiplier is a different story. Moving from "lightly active" at 1.375 to "very active" at 1.725 changes a 1,728 kcal resting figure by roughly 600 calories a day, and the descriptions attached to those multipliers are vague enough that most people can talk themselves into two adjacent categories. If your results do not match the calculation after a fortnight, this is almost always why.
Why 1.62 g/kg matters more than a percentage
Percentage-based splits produce odd results because they scale protein with total calories rather than with your body. Cut calories and your protein target falls, precisely when preserving lean mass matters most. The sports-nutrition literature works in grams per kilogram for that reason, and Morton's meta-analysis of 49 trials found the benefit for fat-free mass flattening out around 1.62 g/kg per day. Setting protein in grams per kilogram first, then filling the remaining calories with carbohydrate and fat, is the more defensible order of operations.
The 40-40-20 rule, examined
This split assigns 40% of calories to carbohydrate, 40% to protein and 20% to fat, and it is one of the most searched macro questions there is. Two observations. Protein at 40% is above the 10–35% adult range, which is not a safety warning for a healthy person but does place it outside official guidance. And fat at 20% sits exactly on the lower boundary — going any lower starts to squeeze the essential fatty acids and the fat-soluble vitamins that depend on dietary fat for absorption.
Precision to the gram is theater
The Atwater factors of 4, 4 and 9 kcal per gram are population averages. Fiber delivers substantially less than 4. Food labels are permitted meaningful tolerances. Absorption varies between individuals and between foods. A target of "2,178 calories and 109 grams of protein" carries four significant figures of implied accuracy that the inputs cannot support. Round to the nearest 50 calories and the nearest 5 grams, and spend the saved effort on consistency instead.
When percentages stop being the right tool
For most people eating to a moderate goal, percentage splits work fine. They break down at the extremes. On a very low calorie intake, a percentage-based protein target can fall below what is needed to protect lean mass. For a large athlete on a high intake, the same percentage can produce a protein figure well past any measurable benefit. In both cases, anchoring protein to bodyweight and treating carbohydrate and fat as the flexible remainder gives a more sensible answer.
Limitations & Accuracy Notes
- The Mifflin-St Jeor equation was derived from 498 adults and explains about 71% of the variation in resting energy expenditure. Roughly a third of the variation between individuals is not captured, so your true requirement may sit meaningfully above or below the estimate.
- Activity multipliers are self-reported categories with no precise definition. They are the single largest source of error in any calculator of this kind, and they systematically flatter people who overestimate how active they are.
- The Acceptable Macronutrient Distribution Ranges describe intakes associated with reduced chronic disease risk in the general population. They are not targets, and sitting outside them is not automatically harmful — several established dietary approaches are outside them by design.
- The 1.62 g/kg plateau comes from resistance-training studies in healthy adults. It does not necessarily transfer to older adults, whose protein needs appear higher, to people in a severe calorie deficit, or to anyone with kidney disease, for whom protein intake is a medical question.
- This tool does not know your medical history. Anyone pregnant, managing diabetes or kidney disease, or with a history of disordered eating should get targets from a registered dietitian rather than a calculator.
Frequently Asked Questions
What is the 40-40-20 rule for macros?
Which macro calculator is most accurate?
How much protein do I actually need?
How many calories are in one gram of each macro?
Can I use this if I already know my calorie target?
How many calories are in each macronutrient?
Should I set protein by total weight or lean mass?
Do the macro ratios matter more than total calories?
Is a low-carb split better?
Do I need to hit my macros exactly?
Is this medical or dietary advice?
References & Further Reading
- Mifflin MD, St Jeor ST et al. — A new predictive equation for resting energy expenditure in healthy individuals — Am J Clin Nutr 1990;51(2):241-7 — the equation used here, derived from 498 adults (R² = 0.71)
- Institute of Medicine — Acceptable Macronutrient Distribution Ranges — The official DRI table behind the 45–65% / 20–35% / 10–35% adult ranges used throughout this page
- Morton RW et al. — Protein supplementation and resistance training: systematic review and meta-analysis — Br J Sports Med 2018;52(6):376-384 — 49 studies, 1,863 participants, and the 1.62 g/kg/day plateau