Data Source and Methodology
This calculator estimates your Basal Metabolic Rate (BMR) using the **Mifflin-St Jeor equation**, which is widely regarded by nutrition experts as one of the most accurate methods.
- Authoritative Source: "A new predictive equation for resting energy expenditure in healthy individuals."
- Citation: Frankenfield, D. C., Muth, E. R., & Rowe, W. A. (2005). Journal of the American Dietetic Association, 105(5), 775-780.
- Reference: DOI: 10.1016/j.jada.2005.02.003
Your BMR is then multiplied by an activity factor to determine your Total Daily Energy Expenditure (TDEE). All calculations are based strictly on the formulas and data provided by this source.
The Formulas Explained
The calculation is a three-step process: 1. **Calculate Basal Metabolic Rate (BMR):** The calories your body burns at complete rest.
Glossary of Variables
- Basal Metabolic Rate (BMR): The minimum number of calories your body needs to perform basic, life-sustaining functions at rest.
- Total Daily Energy Expenditure (TDEE): Your BMR plus the calories you burn from all other activities, including exercise and daily movement. This is the amount of calories you need to eat to *maintain* your current weight.
- Activity Factor: A multiplier (from 1.2 to 1.9) that represents your overall physical activity level.
- Caloric Surplus: The number of extra calories you eat *above* your TDEE to promote weight gain. A surplus of 500 calories per day typically leads to a gain of approximately 1 lb (0.5 kg) per week.
How It Works: A Step-by-Step Example
Let's calculate the target calories for a **28-year-old male** who is **180 cm** tall, weighs **75 kg**, is **moderately active**, and wants a **standard gain** (+500 kcal).
- Calculate BMR (Male):
$ \text{BMR} = (10 \times 75) + (6.25 \times 180) - (5 \times 28) + 5 $
$ \text{BMR} = 750 + 1125 - 140 + 5 = 1740 \text{ kcal/day} $ - Calculate TDEE (Moderately Active = 1.55):
$ \text{TDEE} = 1740 \times 1.55 = 2697 \text{ kcal/day} $ - Calculate Target Calories (Standard Gain = +500):
$ \text{Target} = 2697 + 500 = 3197 \text{ kcal/day} $
To achieve his goal, this individual should aim to consume approximately **3,197 calories per day**.
Frequently Asked Questions
What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy you burn in a coma—just enough to keep your organs functioning. TDEE (Total Daily Energy Expenditure) is your BMR *plus* all the energy you burn from moving, digesting food, and exercising. Your TDEE is your "maintenance" calorie number; eating this amount will keep your weight stable.
How fast should I realistically aim to gain weight?
For most people, a "Standard Gain" of 0.5 to 1.0 lb (0.25 to 0.5 kg) per week is a sustainable and healthy target. This rate minimizes fat gain and maximizes the potential for muscle growth (if combined with resistance training). Gaining faster often results in a higher percentage of fat accumulation.
Why am I not gaining weight even though I'm eating my target calories?
There are a few common reasons:
- Inaccurate Tracking: You may be underestimating your portions or forgetting to log drinks, sauces, and oils, which are calorie-dense.
- Overestimating Activity: You may have selected an activity level that is higher than your actual average, resulting in a TDEE (and target) that is too high.
- Metabolic Adaptation: Your body is an adaptive machine. As you gain weight, your BMR and TDEE will slowly increase, requiring you to eat slightly more to continue gaining at the same rate.
What about macros (protein, carbs, fat)?
This calculator focuses on total calories, which is the most important factor for weight change. However, for quality weight gain (i.e., muscle), macronutrient distribution is key. A common recommendation is:
- Protein: 1.6 - 2.2 grams per kg of body weight (or ~0.8 - 1 gram per lb).
- Fat: 20-30% of your total target calories.
- Carbohydrates: The remaining calories after protein and fat are allocated.
Mifflin-St Jeor vs. Harris-Benedict: Which is better?
The Harris-Benedict equation was created in 1919. The Mifflin-St Jeor equation was developed in 1990. Multiple modern studies, including the one cited as our source, have found the Mifflin-St Jeor equation to be significantly more accurate for today's population. We use it to provide you with the most reliable estimate possible.
Health and nutrition content verified by Dr. Evelyn Reed, RDN, LDN.
Last accuracy review:
Formula (LaTeX) + variables + units
$ \text{BMR (Men)} = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age}) + 5 $
$ \text{BMR (Women)} = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age}) - 161 $
$ \text{TDEE} = \text{BMR} \times \text{Activity Factor} $
$ \text{Target Calories} = \text{TDEE} + \text{Caloric Surplus} $
- No variables provided in audit spec.
- Home — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/ - Health & Fitness — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/health-fitness - Diet & Nutrition — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/subcategories/diet-nutrition - DOI: 10.1016/j.jada.2005.02.003 — doi.org · Accessed 2026-01-19
https://doi.org/10.1016/j.jada.2005.02.003 - TDEE Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/tdee - BMR Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/bmr - Macro Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/macro - Body Fat Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/body-fat
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.