Methodology
How this calculator actually works
Eight science-backed formulas, a confidence model you can trust, a 14-day calibration loop, and visible safety guardrails. No black box.
By FitnessVolt. Updated .
1. The 8 formulas we support
BMR (basal metabolic rate) is the base floor - calories your body burns at rest. TDEE is your total daily expenditure. For adults 19 and over, your TDEE comes from the 2023 DRI EER equations and the BMR shown beside it is Mifflin-St Jeor. Under 19, the calculator uses Mifflin-St Jeor. Enter your body fat percentage and the calculator switches to Katch-McArdle, which works from your lean mass: your BMR comes from it, and your TDEE is built on that BMR. Enter body fat and pick a sport under Sport / Discipline, and it uses Cunningham instead. You can compare all eight formulas side-by-side in your result.
| Formula | Best for | Needs | Year |
|---|---|---|---|
| 2023 DRI EER | Default TDEE for adults 19+. Fitted to doubly labeled water measurements of total daily expenditure. | Age, sex, weight, height, activity | 2023 |
| Mifflin-St Jeor | The BMR shown in your result. Best-tested static formula for the general population. | Age, sex, weight, height | 1990 |
| Harris-Benedict (original) | Historical reference. Tends to overestimate for modern adults. | Age, sex, weight, height | 1919 |
| Harris-Benedict (revised) | Classic clinical reference. Slightly overestimates for modern sedentary adults. | Age, sex, weight, height | 1984 |
| Katch-McArdle | Lean or muscular people who know their body fat. Used when you enter body fat and leave Sport / Discipline on General Fitness. | Weight, body fat % | 1996 |
| Cunningham | Lean, highly trained people. From a 1980 reanalysis of healthy adults; higher intercept than Katch-McArdle. Used when you enter body fat and pick a sport. | Weight, body fat % | 1980 |
| Schofield | WHO-endorsed baseline used in international nutrition standards. | Age, sex, weight | 1985 |
| Owen | Weight-only resting equations. A quick cross-check on the others. | Sex, weight | 1986-87 |
No single formula is "most accurate" for every person - each one has a population it fits best and a population it misses. The real accuracy gain comes from calibration, not from picking a different starting formula.
2. Why the 2023 DRI EER is the new default
The 2023 Dietary Reference Intakes (DRI) refresh updated the Estimated Energy Requirement (EER) equations using doubly-labeled-water (DLW) measurements - the gold standard for measuring energy expenditure in free-living humans.
DLW tracks two isotopes (deuterium and oxygen-18) as they leave the body, letting researchers back-calculate total daily energy expenditure without guessing at activity. The 2023 equations rest on a much larger DLW dataset than the 2005 EER equations they replace.
We default to DRI EER for adults 19 and older. Under 19, the calculator uses Mifflin-St Jeor instead.
National Academies of Sciences, Engineering, and Medicine (2023). Dietary Reference Intakes for Energy.
3. Confidence: Low / Medium / High
Every calorie target on your dashboard shows a confidence label. It is the single most important number to understand. Confidence grows with each weekly check-in that has at least 3 weigh-ins.
Low
Before your first check-in (days 0-6)
We have your inputs and a formula estimate, no observed data yet. Your target could be off by 300+ calories either way. Keep logging weight and calories - the number will tighten quickly.
Medium
Check-ins 1-2 (about days 7-20)
Your first check-in sets the starting point. From the second, we back-calculate an observed TDEE from your weight trend and give it 50% of the estimate, so the target can move if your trend disagrees with the formula.
High
Check-in 3 and on (about day 21+)
Your logged intake and weight trend carry 75% of the estimate at the third check-in and all of it from the fourth. The system keeps nudging the target as your body and training load change.
Confidence is earned by logging: the more weeks you log, the higher your confidence.
4. The 14-day calibration loop
The calculator does not stop after your first number. Every day you log weight and calories, two pieces of data enter a feedback loop:
-
Observed weight change over the week
We average your weigh-ins across the week (you need at least 3 entries for a valid signal - daily fluctuations mean a single reading is noise).
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Average daily calorie intake
If you logged most days, we trust the average. If you skipped days, we mark the week incomplete and wait.
-
Back-calculated observed TDEE
From those two signals we compute an observed TDEE estimate that fits the way your weight changed. That is distinct from the formula estimate. Check-ins need to be 5 to 14 days apart; a longer gap starts the count again.
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Target adjustment
If observed TDEE differs from the current target, we nudge the target - never more than 200 calories per check-in, and never below the calorie floor - so next week aligns with your goal. The dashboard shows the change and the reason.
After two weekly check-ins (about 14 days), your own trend carries half the estimate and the target can start to move. By the fourth check-in, the calibrated TDEE is based on your logged trend, not a population average.
5. Safety promise
Safety is not a marketing line - it is enforced in code. Every calorie target runs through the same guardrails before it appears on your screen.
Minimum calorie floor
The calculator never sets a daily target below the higher of your BMR x 1.2 or 1,200 kcal for women and 1,500 kcal for men, and a fat-loss deficit never goes past 25% of your TDEE or a loss of 1% of your body weight per week. If your goal rate would break either limit, the target stops at the limit and the result tells you why. For a very small or very sedentary person that minimum can sit above their TDEE; a fat-loss target then stays at TDEE, with no deficit, and the result says to talk to a doctor first.
Diet breaks on long cuts
Plan a 1-2 week diet break at maintenance every 8-12 weeks of dieting, as our weight loss guide explains. The tracker does not schedule the break for you, so put it in your plan when you start a long cut.
RED-S risk detection
Relative Energy Deficiency in Sport has 3 severity tiers. We estimate your energy availability from logged intake, logged training time and fat-free mass, and raise a visible warning with a medical disclaimer when it stays below 30 kcal per kg of fat-free mass on 3 or more days in a week.
Anti-diet-culture stance
No scale-shame copy, no "cheat day" language, no stigmatization of body size.
6. What this calculator does NOT do
Honesty about the edges is part of the product.
- It does not replace a registered dietitian or physician. For medical nutrition therapy, clinical eating-disorder care, or managed chronic conditions, please work with a licensed professional.
- It does not diagnose medical conditions. The RED-S and deficit-duration flags are risk indicators, not diagnoses.
- It does not work out energy needs for pregnancy or breastfeeding. Those change from one stage to the next, so set them with your doctor, midwife or a registered dietitian.
- It does not perform OCR on food photos or scan meals visually. You log food by search, barcode, or saved meal.
- It does not time macronutrients by the hour. Daily totals are what the science supports.
- It does not guess harder when your inputs are off - it corrects through observed weight change. Logging beats input precision.
- It does not share, sell, or advertise on your logged data. See the privacy policy.
Frequently asked questions
Which TDEE formula should I use?
For adults 19 and over, the calculator estimates TDEE with the 2023 DRI EER equations. The BMR it shows is Mifflin-St Jeor. Enter your body fat and it switches to Katch-McArdle; enter body fat and pick a sport under Sport / Discipline, and it uses Cunningham. Both work from lean mass. The bigger accuracy gain comes from calibrating with your logged weight and calories, not from picking a different formula.
What does "Low / Medium / High" confidence mean?
Low means you have not done a weekly check-in yet. Your target is a formula estimate and can be off by 300 calories or more either way. Medium comes with your first two check-ins: the first sets the starting point, and the second compares the two weeks and counts for 50% of the estimate, so your target can move from the second check-in. High starts at your third check-in (75% of the estimate) and reaches 100% from the fourth.
Why did my calorie target change?
Each weekly check-in compares your logged intake with your weight trend. If your weight moved faster or slower than the estimate predicts, your observed TDEE differs from the estimated one, and from your second check-in the target moves toward it in small steps. Your dashboard lists each change under "Why your calories changed".
Is a calorie deficit safe?
Only within limits. The calculator never sets a daily target below the higher of your BMR x 1.2 or 1,200 kcal for women and 1,500 kcal for men, and a fat-loss deficit never goes past 25% of your TDEE or a loss of 1% of your body weight per week. If your goal rate would break either limit, the target stops at the limit and the result tells you why. For a very small or very sedentary person that minimum can sit above their TDEE; a fat-loss target then stays at TDEE, with no deficit, and the result says to talk to a doctor first. It also estimates energy availability from your logged intake, logged training time and fat-free mass, and shows a warning when it looks too low.
What does this calculator NOT do?
It does not replace a doctor or dietitian, and it does not diagnose medical conditions. It does not estimate macronutrient timing down to the hour. It does not perform OCR on food photos. Activity estimates from self-reported training are approximate, so the calculator corrects them with your observed weight change. If you need medical nutrition therapy, please work with a qualified professional.
Ready to run the numbers?
Thirty seconds to your first estimate. About fourteen days until your own weight trend starts steering it.
Open the calculatorBuilt from measured metabolism research, not a generic multiplier alone.
These pages use published energy-expenditure research as the starting point, then the app improves the estimate with your logged weight and intake patterns when you calibrate.