What TDEE means, in plain English
TDEE stands for Total Daily Energy Expenditure. It’s the total number of calories (kcal) you burn over 24 hours — not just during a workout, but everything put together: keeping your heart beating, digesting lunch, walking the dog, and taking the elevator instead of the stairs. If you consistently eat right at your TDEE, your weight stays the same. Eat less and you lose; eat more and you gain.
Three things drive TDEE: your basal metabolic rate (what your body burns at rest, roughly 60–75% of the total), the thermic effect of food (the calories your body spends digesting meals, ~10%), and everything you physically do — structured exercise, incidental walking, fidgeting, standing at your desk (NEAT, ~15–30%).
How this calculator works
We use the Mifflin–St Jeor equation to estimate your BMR from your age, sex, height and weight. It’s the equation most commonly used by Canadian dietitians and sports-nutrition researchers because it tends to be more accurate than the older Harris–Benedict formula for today’s adults.
The BMR formula:
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
We then multiply BMR by an activity factor (1.2 to 1.9) to estimate your TDEE. The three result cards at the bottom of the tool show your maintenance kcal, a ~500 kcal/day deficit for sustainable fat loss, and a ~250 kcal/day surplus for a lean gain. We floor the deficit at 1,200 kcal because anything under that almost guarantees nutrient gaps and is a job for a registered dietitian, not a calculator.
Picking your activity level honestly
The most common reason TDEE estimates come out too high is people overestimate how active they are. Sedentary isn’t lazy — it just means “desk job with no structured exercise.” If you’re not sure, pick one level lower than you think and recalibrate after a few weeks.
- Sedentary (1.2): desk job, barely any walking, no workouts.
- Lightly active (1.375): desk job + 1–3 short workouts a week or a lot of walking.
- Moderately active (1.55): 3–5 dedicated workouts a week, or a non-desk job.
- Very active (1.725): 6–7 hard workouts a week, or a physically demanding job.
- Athlete (1.9): full training load plus a physical job — construction, serving, coaching.
Using TDEE to lose, gain or maintain
A pound of body fat stores roughly 3,500 kcal, so a 500 kcal/day deficit averages about half a kilo of fat loss per week. That’s a realistic, sustainable pace that most people can maintain without wrecking energy levels or hunger. For lean gain, a 200–300 kcal/day surplus paired with resistance training is the evidence-based range — more than that mostly becomes fat.
Reassess every 2–3 weeks. If the scale hasn’t moved in the direction you expected, your estimated TDEE is probably 100–200 kcal off your real number. Adjust, log a week or two, and reassess again. This is slower than most internet diets promise and more reliable than any of them.
When TDEE isn’t enough
TDEE is a screening estimate. It doesn’t account for thyroid conditions, PCOS, pregnancy, breastfeeding, specific medications, or the deep metabolic adaptations that can happen after years of restrictive dieting. If any of those apply, book a conversation with a registered dietitian — the College of Dietitians of Ontario and Dietitians of Canada both maintain searchable directories.
Frequently asked questions
What is TDEE?
TDEE stands for Total Daily Energy Expenditure — the total number of calories (kilocalories) you burn in a typical 24-hour period. It includes your resting metabolic rate (what you burn just to exist), the thermic effect of food (what it costs to digest), and all the movement you do during the day.
How is TDEE calculated?
We use the Mifflin–St Jeor equation, which is the equation most commonly recommended by dietitians and sports-nutrition researchers. It estimates your basal metabolic rate (BMR) from your sex, age, weight and height, and then multiplies that by an activity factor between 1.2 (sedentary) and 1.9 (athlete) to account for everything you do on top of just being alive.
How accurate is the Mifflin–St Jeor equation?
For most healthy adults, Mifflin–St Jeor is accurate to within about 10% of true energy needs. It tends to be less accurate at the extremes — very lean athletes, people with significant obesity, or people with medical conditions that affect metabolism. If your real-world intake doesn’t match the estimate after 2–3 weeks, adjust by 100–200 kcal/day and reassess.
Should I use TDEE to lose or gain weight?
TDEE is the maintenance number — the intake at which you’d neither lose nor gain weight. For a steady, sustainable fat loss of roughly half a kilo per week, subtract 400–500 kcal/day from your TDEE. For a lean gain of roughly a quarter kilo per week, add 200–300 kcal/day. Don’t chase faster rates than that unless you’re working with a registered dietitian — the data is clear that aggressive deficits hurt adherence and performance.
Which activity level should I choose?
"Sedentary" is a desk job with no structured exercise. "Lightly active" is a desk job plus 1–3 short workouts a week or a lot of walking. "Moderately active" is 3–5 dedicated workouts a week. "Very active" is 6–7 workouts a week or a physically demanding job like construction. "Athlete" is a full training load plus a physical job. When in doubt, pick one level lower than you think — people consistently overestimate their activity.
Is TDEE the same as BMR?
No. BMR (basal metabolic rate) is what you’d burn if you lay in bed all day, doing absolutely nothing. TDEE is BMR plus everything else — digestion, walking around, exercise, fidgeting. TDEE is always higher than BMR.
Does UnityLife store my TDEE inputs?
No. Every calculation happens entirely in your browser. Nothing you enter — age, weight, height, sex, activity level — is sent to our servers or saved anywhere. Close the tab and it’s gone.
Sources & further reading
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” American Journal of Clinical Nutrition, 1990.
- Health Canada — Dietary Reference Intakes: Energy, Carbohydrate, Fibre, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.
- Dietitians of Canada — Find a Dietitian: dietitians.ca/find-a-dietitian.