Live Mifflin vs Harris–Benedict dual strip - so one resting equation never pretends to be measured metabolism.
Educational resting sketch. Formula ≠ metabolism. Not medical advice, lab calorimetry, or a daily calorie prescription.
By Ahmet C. Toplutaş·Site owner & editor · Health tools
Last updated May 21, 2026 · Reviewed May 21, 2026 · Planning estimates only - not tax, medical, or investment advice
01
Basal metabolic rate tools feel authoritative because they return a single neat calorie number. That number is a regression from study populations, not a metabolic cart strapped to your face. Change the published equation - keep the same age, height, weight, and sex coefficient - and the “answer” moves.
Treating one formula as destiny is how meal plans get overconfident. Mifflin–St Jeor and revised Harris–Benedict are both widely cited; they often disagree by tens to a few hundred kcal on the same body. That gap is information, not a bug.
This page’s framing is Formula ≠ metabolism. The panel runs both equations live, names Mifflin as the primary planning default, and shows the delta so “I got a BMR” is not mistaken for “I measured my resting burn in a lab.”
Coaches, clinicians-in-training, and self-trackers hit the same trap: screenshotting one calculator and arguing with another that used a different regression. Naming the equation first is the literacy skill; the arithmetic is secondary.
Decision framing: “Which resting equation am I using, and how far does its twin sit?” - not “which app gave me the number I wanted?”
02
BMR estimates the energy to keep you alive at complete rest - organs, brain, temperature control - under standardized conditions. Related terms like RMR (resting metabolic rate) are close cousins measured with slightly different protocols. For planning sketches, people often use the labels loosely; this page sticks to BMR as “resting equation output.”
BMR is not steps, not training burn, not the thermic effect of food, and not a license to eat only that number. Those layers belong to daily expenditure (TDEE) and to clinical care when needed.
Lean mass, hormones, medications, illness, and adaptive responses can push real resting burn away from any equation. When body composition matters more than scale weight, pair this page with the body fat calculator for context - still not a lab VO₂ measure.
Think of BMR as the idle power draw on a device spec sheet: useful for sizing, wrong as the only number on your electricity bill. The dual strip keeps you honest about which “spec sheet” you grabbed.
03
The unique affordance here is a side-by-side Mifflin vs Harris–Benedict strip with an explicit equation delta. Same inputs; two regressions; one gap labeled in kcal and percent. That is equation literacy - different from the TDEE page’s rest→day bridge and activity ladder, which multiply a single BMR by movement factors.
Mifflin is marked primary because many modern nutrition references prefer it for non-obese adults. Harris–Benedict remains common in older worksheets and some clinical habits. Showing both prevents silent formula-shopping.
When the delta is large relative to your goals, treat BMR as a band, not a pinpoint - then let weigh-ins and adherence edit the plan, not another random online tool.
Absolute deltas grow with body size; percent deltas tell you how loud the disagreement is relative to the primary. A 80 kcal gap on a 1,700 kcal Mifflin is a different planning story than the same gap on a much smaller estimate.
Try the Metric · adult M and Older adult presets and compare how the delta shifts with age and size.
04
Mifflin–St Jeor (1990): 10×kg + 6.25×cm − 5×age, then +5 (male coefficient) or −161 (female coefficient). Revised Harris–Benedict (1984) uses different slopes and intercepts for each coefficient set. Both expect metric kilograms and centimeters internally; the panel converts imperial inputs first.
Sex coefficients come from the published samples. They are formula knobs for this educational sketch - not a full account of gender identity, hormone therapy, or intersex variation. If that mismatch matters for your body, use clinical guidance and measured RMR when available.
Neither equation “wins” every body. Validation studies vary by age, BMI band, and ethnicity of the sample. The dual strip’s job is transparency, not crowning a permanent champion.
05
Metric and imperial toggles convert weight and height when you switch, so you are not stuck retyping. Garbage in still wins: mixing stones with pounds, or entering height in feet while the field expects inches, will invent a confident wrong BMR.
Use a recent morning weight if you track one, and a measured height. Clothing, glycogen, and sodium swing the scale; BMR equations will dutifully chase that noise if you update obsessively. Prefer weekly averages when the number is for planning, not vanity.
The per-kg line under the verdict (kcal per kilogram) is a quick intensity read - not a separate formula. It helps you notice when an input typo made BMR absurdly high or low for body size.
06
Eating at BMR long-term is usually an aggressive underfuel pattern for anyone who walks, works, or trains. Daily needs live on the TDEE calculator, which owns the BMR ≠ TDEE framing with a rest→day bridge and activity ladder. Macro splits then belong on the macro calculator.
This page deliberately stops before activity multipliers so the dual-formula story stays sharp. If you need session burn estimates instead, use calories burned.
Educational disclaimer: not medical or diet advice. Pregnancy, eating disorders, endocrine disease, and medications need qualified care. If calorie counting is distressing, stop and seek support.
For goal-oriented calorie sketches after you leave resting math behind, the related calorie calculator and TDEE tools are the next rung - still educational, still not prescriptions.
07
Example A · Metric adult F. Preset: 30y, 65 kg, 165 cm. Read Mifflin as primary, then note Harris delta - often tens of kcal, sometimes more.
Example B · Metric adult M. Preset: 35y, 82 kg, 178 cm. Larger bodies can widen absolute deltas even when percent gaps look modest.
Example C · Imperial. Preset: pounds and inches. Confirm the unit toggle before trusting the verdict - unit mistakes dwarf formula disagreements.
Example D · Older adult. Preset: age 62. Watch how age terms pull both equations down and whether the delta changes shape versus the younger presets.
After presets, enter your own stats once, share the link if you want a snapshot, and move to TDEE only when you need a full-day sketch - not because a resting number felt too low for lunch.
When two apps disagree, check which equation each used before you change your meal plan. Formula ≠ metabolism includes “formula ≠ the other website’s formula.”
08
Most “wrong BMR” fights are unit errors, diet-target confusion, or silent equation swaps - not broken algebra.
09
Share links snapshot sex coefficient, units, and body stats. Live typing never rewrites the address bar.
10
Stop here for resting-equation literacy and Formula ≠ metabolism. Hand off for daily burn, macros, composition estimates, or clinical calorimetry.
11
BMR equations are population regressions - useful sketches of resting burn, not a direct reading of your mitochondria. Two respected formulas can disagree by a meaningful kcal gap on the same body. This page’s framing is Formula ≠ metabolism so that gap stays visible instead of hidden behind one confident number.
Mifflin–St Jeor (1990) as the primary planning default, and revised Harris–Benedict (1984) as the dual-formula mirror. Both use sex-coefficient, age, height, and weight. Neither is a lab metabolic cart or doubly labeled water measurement.
It evaluates the same inputs under Mifflin and Harris–Benedict side by side and labels the delta. That equation literacy affordance is different from the TDEE page’s rest→day bridge and activity ladder, which multiply one BMR by movement factors.
No. BMR is resting burn only. Daily needs (TDEE) add activity. Using BMR alone as a diet target is usually too low. Hand off to the TDEE calculator when you need a full-day sketch.
The published regressions include sex-specific constants from the original study samples. They are formula coefficients for this educational sketch, not a clinical assessment of gender, hormones, or body composition. Athletes and people with atypical lean mass may diverge further - consider body-fat–aware tools when relevant.
No. Educational only. Pregnancy, clinical conditions, medications, and disordered eating need a qualified clinician or registered dietitian. If calorie math is distressing, step away and seek support.
No. Values hydrate from the URL on load; the address bar updates only when you use Share or Copy.
LIVE BMR · DUAL FORMULA
Formula ≠ metabolism ↓Body presets
Mifflin–St Jeor BMR (primary)
1,370 kcal
Resting sketch · ≈ 21.1 kcal / kg · not a daily diet target
MIFFLIN–ST JEOR
Primary · 1990
1,370 kcal
Active primary
HARRIS–BENEDICT
Revised · 1984
1,430 kcal
Mirror equation
EQUATION DELTA
+60 kcal(+4.4% vs Mifflin)
Same body, two regressions. Formula ≠ metabolism - pick a primary for planning, then sanity-check the gap before treating either as lab truth.
BMR ≠ daily calories
This page stops at resting burn and equation literacy. For activity multipliers and a full-day sketch, open the TDEE calculator - that page owns BMR ≠ TDEE with a rest→day bridge.
Copy the link to save or share your results.