BMR & TDEE calculator
Updated 2026-07-06
Before you can set a sensible calorie target, you need to know roughly how much energy your body uses in a day. Diet2Fit's BMR/TDEE calculator gives you that starting point in under a minute. This guide explains what the two numbers mean, how they're estimated, and the one place almost everyone gets it wrong.
BMR: your engine at idle
BMR (Basal Metabolic Rate) is the energy your body burns just to stay alive — heartbeat, breathing, brain activity, keeping warm — if you did nothing but rest all day. It's your engine idling. Even a very sedentary person burns well over a thousand calories a day this way; for most adults, BMR is the single largest share of daily calorie burn.
Diet2Fit estimates BMR using the Mifflin-St Jeor equation, a widely used formula based on your weight, height, age, and sex. It's the same equation most dietitians reach for first, because across studies it tends to be the most reliable of the standard formulas for the general population.
One thing to be clear about: this is an estimate, not a measurement. Actually measuring metabolic rate requires lab equipment. Any formula — including this one — can be off by a couple of hundred calories for a given individual, because metabolism varies with muscle mass, genetics, and more. That's fine: an estimate is exactly the right starting point, as long as you treat it as one.
TDEE: your real daily burn
TDEE (Total Daily Energy Expenditure) is your BMR plus everything else you do — walking to the metro, climbing stairs, cooking, fidgeting, and your workouts. It's calculated by multiplying your BMR by an activity multiplier:
| Activity level | Roughly means | Multiplier |
|---|---|---|
| Sedentary | Desk job, little exercise | ~1.2 |
| Lightly active | Exercise 1–3 days/week | ~1.375 |
| Moderately active | Exercise 3–5 days/week | ~1.55 |
| Very active | Hard exercise 6–7 days/week | ~1.725 |
| Extremely active | Physical job + hard training | ~1.9 |
TDEE is the number that actually matters for your goal: eat around your TDEE and your weight roughly holds; eat consistently below it and you lose; above it and you gain.
The tip: pick a lower activity level than you think
Here's the honest truth — most people overestimate their activity level, and it's the single biggest source of error in this whole calculation. Three gym sessions a week feels "very active", but if the other 165 hours of your week are spent at a desk, in a car, and on a sofa, "lightly active" is usually closer to reality. Picking one level too high can inflate your TDEE by 200–300 calories a day — enough to quietly erase months of expected progress and leave you wondering why the plan "isn't working".
Our rule of thumb: when torn between two levels, choose the lower one. If you then find yourself losing weight faster than intended, you can always adjust upward. Err the other way and you'll spend weeks confused instead.
How Diet2Fit uses these numbers
Your TDEE becomes the anchor for your daily calorie target. Depending on your goal, your target sits at a sensible margin below TDEE (for fat loss), around it (for maintenance), or above it (for muscle gain) — and your weekly meal plan is then built to land near that target while keeping meals balanced. Your weight check-ins over the following weeks are the reality check: if the trend on your Progress tab doesn't match the plan's intent after three to four weeks, the estimate gets corrected by real data, which always wins.
A necessary caveat
These calculators are general-purpose tools for healthy adults. If you're pregnant or breastfeeding, under 18, have a thyroid or other metabolic condition, or a history of disordered eating, please set calorie targets with a doctor or registered dietitian rather than a formula.
Still stuck? Email contact@diet2fit.com — a human reads every message.