When you set up a calorie target, a number appears: maybe 1,800, maybe 2,300. It feels precise. It isn’t, and that’s okay, as long as you know where it comes from and how to use it.
This guide explains the two ideas behind most calorie targets, BMR and TDEE, and the honest limits of both.
BMR: what your body spends at rest
BMR (basal metabolic rate) is the energy your body would use in a day if you did nothing at all: breathing, circulating blood, repairing cells, keeping your temperature stable. For most people, it’s the largest share of daily energy use.
BMR isn’t something an app can measure directly. It’s estimated from a few personal details: weight, height, age, and sex. HealthTrac AI uses the Mifflin-St Jeor equation, which is widely used in nutrition practice and has been found to be one of the more reliable predictive formulas for the general population:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
TDEE: what you spend in a whole day
TDEE (total daily energy expenditure) is BMR plus everything else you do. It has four parts:
- BMR: the baseline.
- Daily movement: walking, chores, fidgeting, standing.
- Exercise: intentional workouts.
- Digestion: your body uses some energy simply processing food.
To estimate TDEE, the formula multiplies BMR by an activity factor:
Activity level | Typical description | Multiplier |
|---|---|---|
Sedentary | Desk job, little exercise | 1.2 |
Lightly active | Light exercise 1–3 days/week | 1.375 |
Moderately active | Moderate exercise 3–5 days/week | 1.55 |
Very active | Hard exercise 6–7 days/week | 1.725 |
Extremely active | Physical job plus hard training | 1.9 |
A worked example
Take a 35-year-old woman who weighs 70 kg and is 165 cm tall.
- BMR: (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 700 + 1,031 − 175 − 161 ≈ 1,395 calories
- She exercises lightly a few days a week, so we multiply by 1.375.
- TDEE: 1,395 × 1.375 ≈ 1,918 calories
That’s roughly the number of calories she’d need to maintain her current weight.
From TDEE to a daily target
Your TDEE is a maintenance estimate. Your goal adjusts it:
- Maintain weight: eat near your TDEE.
- Lose weight: eat somewhat below it. A common starting point is a modest calorie reduction chosen for your circumstances. Weight change varies over time, so a fixed reduction does not guarantee a particular weekly loss.
- Gain weight: eat somewhat above it.
Slow and modest adjustments are usually easier to sustain than aggressive ones. Very low calorie targets aren’t appropriate for most people without medical supervision.
The limits: why it’s only an estimate
Be wary of anyone, or any app, that treats a calorie number as exact. Here’s why:
- Formulas describe averages. Two people with identical stats can differ in actual BMR by a couple hundred calories a day, because of muscle mass, genetics, hormones, and medical conditions.
- Activity levels are self-reported. Most of us misjudge how active we are, often overestimating.
- Body composition isn’t included. Muscle burns more energy than fat, but the formula doesn’t know your muscle mass.
- Food logs aren’t perfectly accurate either. Portions, labels, and restaurant meals all carry error.
- Your needs change. Weight, sleep, stress, illness, and training all shift your real expenditure.
Some people shouldn’t rely on formula-based targets at all, including those who are pregnant or breastfeeding, who have a medical condition, who are under 18, or who have a history of disordered eating. If that’s you, work with a doctor or registered dietitian.
How to use your number well
- Treat it as a hypothesis. Follow it for two to four weeks.
- Check the trend. If your weight is moving in the direction you want, the estimate is working for you.
- Adjust, don’t agonize. If your weight isn’t changing as expected, review the completeness of your logs and discuss an appropriate adjustment with a registered dietitian if needed.
- Set your own target when needed. If a healthcare professional gives you a different number, use it. HealthTrac AI lets you choose your own calorie target rather than the calculated one.
The bottom line
BMR is what your body burns at rest, TDEE is what it burns across a full day, and your calorie target is just TDEE nudged toward your goal. The math is a sensible place to start, and your own real-world results are what refine it.
This article is for general education and isn’t medical advice. Talk with a healthcare professional before making significant changes to your diet.