BMR Formula Comparison: Which Calculator Is Most Accurate?

The Three Main BMR Formulas

When you use a BMR calculator, it's actually using a math formula in the background. There are three main formulas that doctors and scientists use:

1. Mifflin-St Jeor Equation (1990) - The most commonly used today

2. Harris-Benedict Equation (1919, revised 1984) - The classic formula

3. Katch-McArdle Formula - For people who know their body fat percentage

Each formula gives slightly different results. Let's break down which one works best for you.

Mifflin-St Jeor: The Gold Standard

This is the formula we use in our calculator, and here's why:

It was created in 1990 after testing on modern populations, so it's more accurate for today's lifestyles than the older Harris-Benedict formula.

Research shows it's accurate within about 10% for most people. That means if it says your BMR is 1,500 calories, your real BMR is probably between 1,350 and 1,650.

It's simple to use—you only need your age, weight, height, and sex (male or female). No complicated measurements required.

The formula for men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5

The formula for women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

Don't worry about memorizing this—our calculator does the math for you instantly!

Harris-Benedict: The Original

This formula has been around since 1919 and was updated in 1984. It's still used by many calculators and doctors.

The good news: It's been tested for over 100 years and generally works well.

The downside: It tends to overestimate BMR by about 5% compared to the Mifflin-St Jeor formula. That means it might tell you that you burn more calories than you actually do.

If you're using an older calculator or app and getting numbers that seem too high, it might be using Harris-Benedict.

For most people, the Mifflin-St Jeor formula is more accurate, which is why modern calculators (including ours) prefer it.

Katch-McArdle: For The Fitness Enthusiast

This formula is special because it uses your lean body mass (how much muscle you have) instead of just your total weight.

The advantage: If you have a lot of muscle, this formula can be more accurate because muscle burns more calories than fat.

The challenge: You need to know your body fat percentage, which requires special equipment like DEXA scans, body fat calipers, or smart scales. Most people don't have this info.

Who should use it: Athletes, bodybuilders, or anyone who regularly measures their body composition.

Who shouldn't bother: Beginners or casual exercisers. The Mifflin-St Jeor formula will work just fine for you.

Which Formula Should You Use?

Here's our simple recommendation based on your situation:

For 90% of people: Use Mifflin-St Jeor (that's what our calculator uses). It's accurate, easy, and trusted by nutritionists.

If you're an athlete who tracks body fat: Try Katch-McArdle if you have accurate body fat measurements.

If you're comparing to an old calculation: Be aware that Harris-Benedict might give you a number that's 50-100 calories higher than Mifflin-St Jeor.

The honest truth: All three formulas are estimates. Your real BMR could be 10-15% different based on genetics, thyroid function, and other factors the formulas can't account for.

The best approach: Start with one formula (we recommend Mifflin-St Jeor), track your results for 2-3 weeks, and adjust based on what actually happens with your weight.

Why Estimates Are Still Useful

Even though no formula is perfect, having an estimate is way better than guessing randomly.

Think of it like a weather forecast. It might say it'll be 75 degrees, but it could actually be 72 or 78. That's still helpful information for deciding what to wear!

The same applies to BMR. Even if the calculator is off by 100-200 calories, you now have a solid starting point to work from.

After a few weeks of tracking, you'll know your true number based on real-world results, not just math.