Three BMR Formulas, One Number: Budgeting Calories That Actually Work
You run the same calculator three times and get three different numbers. The first tool tells you your baseline is 1,650, the second spits out 1,700, and the third insists on 1,740. None of them are "wrong," and all of them are frustrating. Before you throw your phone across the room, here is the truth: a 50 to 100 calorie swing between formulas is normal, expected, and genuinely not a problem for your weight plan.
Why the Formulas Disagree
Every BMR formula is a statistical shortcut. Researchers fit a line to a large group of measured people, and each team used a different sample and a different weighting of weight, height, and age. That is why Mifflin-St Jeor and Harris-Benedict land a little apart even with identical inputs. For the 30-year-old male, 175 cm, 70 kg example from our BMRScope calculator, Mifflin works out to about 1,682 kcal while the revised Harris-Benedict gives roughly 1,703 kcal. A 20-kcal gap is nothing; even at the extremes you rarely see more than 100 to 200 kcal separating common formulas.
Treat the Median as Your Baseline
Instead of trusting any single result, take the approach our methodology page recommends: run two or three formulas and average them. With Mifflin at 1,682 and Harris-Benedict at 1,703, the median sits near 1,692 kcal. That midpoint is your honest starting baseline because it smooths out each formula's individual bias. Your true resting burn almost certainly sits close to that number, give or take 5 to 10 percent.
Turn BMR Into a Daily Budget
BMR is not your calorie allowance; it is the floor your body spends while doing nothing. To budget for the day you multiply it by an activity factor. Sedentary: 1.2. Lightly active: 1.375. Moderately active: 1.55. Very active: 1.725. Athlete: 1.9. For our 1,692 kcal baseline at moderate activity, maintenance lands around 1,692 × 1.55 ≈ 2,622 kcal. That is your break-even number to stay exactly where you are.
A Worked Budget From Start to Finish
Take Maya, a 28-year-old woman, 165 cm, 60 kg, moderately active. Mifflin gives her roughly 1,364 kcal. Her maintenance budget is 1,364 × 1.55 ≈ 2,114 kcal. Want to lose about half a kilo a week? Drop 500 kcal and eat near 1,614. Want to gain slowly? Add 200 to 300 kcal on top of maintenance. The point is that the 20-kcal difference between formulas never moves the plan meaningfully; your activity factor and your tracking accuracy matter far more than which formula you chose.
The Only Number That Truly Matters
Use the median to start, set your budget from the activity multiplier, and then adjust after two to three honest weeks of tracking. If your weight drifts the way you want, keep the number. If not, nudge it by 100 to 150 kcal. That feedback loop — not the formula — is what turns a rough estimate into a personal calorie budget that actually works.
Frequently Asked Questions
Why does my BMR calculator give a different number than another website?
Because each site uses a different formula. Mifflin-St Jeor and Harris-Benedict weight the same inputs differently and use different research samples, so a 50 to 100 kcal gap is common. Run two or three formulas and use the median.
Should I use my BMR directly as my calorie target?
No. BMR is what you burn at complete rest. Your daily budget needs an activity multiplier (about 1.2 to 1.9 depending on movement). Eating exactly at BMR would leave most active people far too little energy.
How much can the formulas disagree in practice?
Usually 100 to 200 kcal at most for the same person. That gap rarely changes a weight-loss or maintenance plan, because most budgets give you room to adjust after a few weeks.
Which formula should I trust for my baseline?
For general diet planning, most dietitians prefer Mifflin-St Jeor. But the safest move is to average two or three formulas as your starting baseline, then adjust based on real-world results.