Calorie / TDEE

How BMR and TDEE Are Calculated

Total Daily Energy Expenditure (TDEE) is roughly how many calories a day it takes to maintain your current weight, factoring in your activity level on top of the calories your body burns at rest. Enter your gender at birth, age, height, weight, and typical activity level, and this calculator estimates your TDEE, along with your Basal Metabolic Rate (BMR) and calorie targets for weight loss or gain.

BMR is the energy your body burns at complete rest just keeping itself running (breathing, circulation, cell repair). TDEE scales that up by how active you actually are day to day, since a sedentary desk job and a physically demanding one burn very different amounts of energy on top of the same BMR.

The Formula

The default BMR formula is Mifflin-St Jeor, the equation most current dietetics guidance recommends over the older Harris-Benedict equation:

$$\vE{\text{BMR}} = 10 \times \vA{\text{Weight (kg)}} + 6.25 \times \vB{\text{Height (cm)}} - 5 \times \vC{\text{Age}} + \vD{s}$$

where $\vD{s}$ is $+5$ for men and $-161$ for women — the equation was derived separately for each from population data, not a unisex average.

Two alternative formulas are also available under “BMR formula”:

• Harris-Benedict (the original, revised in 1984) — an older but still widely-recognized equation, offered mainly for comparison or if a specific plan asks for it by name.
• Katch-McArdle — skips age and gender entirely and instead calculates BMR directly from lean body mass ($370 + 21.6 \times \text{lean mass (kg)}$, where lean mass is your weight minus fat mass). This tends to be more accurate for people who know their actual body-fat percentage, especially athletes and muscular individuals the age/gender-average formulas can underestimate.

$$\vF{\text{TDEE}} = \vE{\text{BMR}} \times \text{Activity Multiplier}$$

Weight-loss calorie targets are shown at three paces — mild (~250 kcal/day deficit, roughly 0.5 lb/week), moderate (~500 kcal/day, roughly 1 lb/week — the traditional “safe and sustainable” default), and extreme (~1,000 kcal/day, roughly 2 lb/week, generally cited as the upper bound for a diet-only approach without medical supervision) — each based on the standard rule of thumb that a pound of fat corresponds to about 3,500 stored calories. None of these targets is ever allowed to drop below 1,200 calories/day, a commonly-used floor for a very-low-calorie diet; if a pace’s true deficit would go lower, the target is capped there instead and flagged as unrealistic for your numbers. The weight-gain target uses a standard ~500 calorie/day surplus, for roughly 1 lb of gain per week.

Zigzag calorie cycling (under “View a Zigzag Calorie-Cycling Schedule”) is an optional alternative way to hit the same moderate-pace weekly total: instead of eating the identical number every day, calories are higher on weekends and lower on weekdays, in a fixed 2-high/5-low pattern sized so the week’s total is arithmetically identical to eating the flat moderate target every single day. This is purely a different day-to-day distribution of the same weekly calories, not a different diet or a different total — some people simply find the variety easier to stick to.

Worked Example

A 30-year-old man, 180 cm tall, weighing 80 kg, who is moderately active:

1. BMR: $10(\vA{80}) + 6.25(\vB{180}) - 5(\vC{30}) + 5 = 800 + 1125 - 150 + 5 = \vE{1780}$ calories/day.
2. TDEE: $\vE{1780} \times 1.55 = \vF{2759}$ calories/day.
3. Weight-loss target: $\vF{2759} - 500 = 2259$ calories/day.
4. Weight-gain target: $\vF{2759} + 500 = 3259$ calories/day.

Key Factors to Consider

• These formulas estimate a population average, not your exact individual metabolism. Genetics, muscle mass, thyroid function, and other individual factors all cause real metabolic variation that no formula based on age/height/weight/gender alone can fully capture — use the result as a starting point, then adjust based on how your actual weight trends over a few weeks of real tracking.
• The 3,500-calories-per-pound rule is a widely-used approximation, not an exact physical constant. Real weight change involves water retention, glycogen stores, and other factors beyond pure fat loss, especially in the first weeks of a calorie change — don’t expect the scale to match the calculated pace exactly week to week, even if the average trend over a longer period tracks reasonably well.
• Activity level is often overestimated, which is one of the most common sources of an inaccurate TDEE. People frequently round up their own activity level, which inflates the TDEE estimate and the resulting calorie targets — being conservative about which activity tier actually matches your typical week produces a more realistic number.
• Katch-McArdle is only as accurate as the body-fat percentage entered. Since this formula relies directly on lean body mass, a body-fat percentage estimate that’s off (from an imprecise measurement method) carries that error directly into the BMR calculation — an accurate body-fat reading matters more here than for the age/gender-based formulas.

Useful to Know

Your TDEE isn’t a fixed number — it drops as you lose weight, and not only because you’re now carrying less mass. A lighter body simply burns fewer calories at rest and during activity, so the same “moderate deficit” that worked at your starting weight becomes a smaller deficit (or none at all) once you’ve lost a meaningful amount of weight, unless you recalculate against your new weight. On top of that, sustained dieting triggers some degree of metabolic adaptation — the body becomes modestly more calorie-efficient than the formula alone predicts, an effect researchers sometimes call “adaptive thermogenesis.” Neither effect means the math is wrong; it means TDEE is a snapshot of today’s numbers, not a permanent target — plan to re-run this calculator every few weeks during an extended diet or bulk, using your current weight, rather than eating to a single figure calculated once at the start.