How the TDEE calculation works
The calculator first estimates basal metabolic rate (BMR): the energy needed for basic body functions at rest. It uses the Mifflin-St Jeor equation, published in 1990 from measured resting energy expenditure in adults. The equation has separate constants for male and female physiology. It then multiplies BMR by an activity factor to estimate total daily energy expenditure (TDEE).
male BMR = 10w + 6.25h − 5a + 5
female BMR = 10w + 6.25h − 5a − 161
TDEE = BMR × activity multiplier
cut target = TDEE × 0.80; bulk target = TDEE × 1.10
w = kilograms, h = centimetres, a = yearsAn activity multiplier compresses work, training, spontaneous movement, and digestion into one broad estimate. That makes the result a starting hypothesis, not a direct measurement. Two people with the same age, height, and weight can have different maintenance needs because their movement, body composition, training volume, and individual energy adaptation differ.
Worked example
For a 30-year-old male at 175 cm and 70 kg, Mifflin-St Jeor estimates BMR at 1,648.75 kcal/day. Selecting moderate activity multiplies this by 1.55, producing maintenance of about 2,556 kcal/day. The cut setting displays about 2,044 kcal, and the bulk setting about 2,811 kcal. At 70 kg, the accompanying protein range is 112–154 grams per day, based on 1.6–2.2 g/kg.
Do not chase a single day's scale reading. Choose a target, keep food measurement reasonably consistent, and compare average body weight across at least two to four weeks. If the trend is materially different from the goal, adjust by a modest amount. Water, glycogen, sodium, digestion, and menstrual-cycle changes can obscure short-term fat or muscle change.
Activity multiplier reference
| Level | Multiplier | Practical example |
|---|---|---|
| Sedentary | 1.2 | Desk-based day; little intentional exercise |
| Light | 1.375 | Easy training or active errands 1–3 days/week |
| Moderate | 1.55 | Purposeful exercise 3–5 days/week |
| Very active | 1.725 | Hard training most days or active occupation |
| Extra active | 1.9 | Heavy physical work plus frequent intense training |
Choosing a target without false precision
A 20% deficit is a conventional moderate cut, not the correct prescription for everyone. Smaller deficits are often easier to sustain and can better support training performance; larger deficits increase fatigue and the chance that an estimate is wrong. A 10% surplus is similarly a conservative starting point, not proof that every extra calorie becomes muscle. Round the output to a practical food target and calibrate against observed change.
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Frequently asked questions
How accurate is a TDEE calculator?
It is a population-based starting estimate, not a metabolic test. Equation error and activity-factor error can easily move the result by several hundred calories. Track average intake and body-weight trend for two to four weeks, then adjust the estimate using your own data.
What calorie deficit should I use for cutting?
This tool shows a 20% deficit as a moderate reference. A smaller deficit may suit leaner people, long cuts, or demanding training; a larger deficit can raise fatigue and adherence risk. Medical conditions, pregnancy, adolescence, or eating-disorder history require qualified clinical guidance.
Which activity level should I choose?
Choose from your whole week, not your hardest workout. Consider occupation, steps, chores, and training frequency together. When between levels, start with the lower multiplier and use two to four weeks of weight and intake data to calibrate rather than repeatedly changing the dropdown.
Why does the calculator show a protein range?
The 1.6–2.2 g/kg range is a practical sports-nutrition reference for many exercising adults, with the lower end often sufficient and the upper end offering flexibility during energy restriction. It is not a medical prescription, and kidney disease or other clinical needs require professional advice.