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How do you find your BMR? Finding your true BMR is the key to weight loss that actually lasts. This post walks you through a real-world process to uncover your numbers and fuel your body right.

Finding Your True BMR: The Patient, Proven Way to Fuel Your Unique Engine

Sometimes the lessons that change everything are not in a book or an online calculator. They show up in the long grind, the months when you are paying attention. For me, that moment came during a study I was fortunate to be part of. It covered a lot, but the thing that changed me, and shined the brightest light on why weight loss is such a fight, was finally learning how to figure out my own Basal Metabolic Rate, or BMR. It’s not a magic number you look up once and file away. It is alive and it shifts all the time.

At the time I started the study I was working with a “nutrition specialist” who had me at roughly 2400 calories a day based on my weight at the time. An online calculator backed them up with a BMR estimate that looked impressive on paper, but where I ultimately landed after the study was half of what both they and the calculator claimed.

Months of tracking and testing taught me exactly why people quit. When the numbers are wrong, you burn yourself out and wonder why all your work is not getting you anywhere.

Before we dig into your bmr

A good mechanic does not guess what is wrong with the engine. They run a real diagnostic that accounts for its quirks, history, and current state. That process was one of the most valuable I have ever gone through.

Finding your true BMR is not a quick answer from a one size fits all online calculator. It is patience, observation, and precision. So stop chasing generic bullshit and learn how to get the number that is yours. This is your guide to becoming the head mechanic of your own body, learning exactly how to fuel the one car you will ever drive.

Before we get into the steps, I want you to take a breath. This process works, but it is not a sprint. It will take patience, attention, and a willingness to adjust as you go. There will be moments when you feel unsure or stuck, and that is normal. If you hit a wall or just need someone to walk through it with you, send me an email. I would rather you ask a question than give up on the process. 

Step 1: Get your body fat percentage

First, get your body fat percentage. Use a method that is accessible and measure the same way each time so you can track changes over time.

Accessible methods to get your body fat percentage

Smart scales that use BIA: Devices like smart scales and handheld sensors use bioelectrical impedance analysis (BIA). They send a weak electrical current through your body to estimate body fat percentage. Hydration affects the results, so measure at the same time of day under similar conditions.

Advanced body scans: Many gyms have sophisticated BIA devices like an InBody or Evolt scanner. These provide a quick, detailed breakdown of body composition, including muscle mass and body fat percentage by region. They are an excellent way to get a precise initial diagnostic.

DEXA scan: Considered the “gold standard” for accuracy, a DEXA, or Dual Energy X ray Absorptiometry, uses low dose X rays to provide precise measurements of body fat, bone density, and muscle mass. It is usually more expensive and found in clinical settings, but it gives the most reliable starting point.

If you have to guess your body fat percentage, here is what happens:

Your initial diagnostic is less precise: Guessing is like a mechanic giving your car a quick visual instead of a full diagnostic scan.

The custom tune up takes longer: Since your starting BMR and TDEE will be a less accurate guess, your test drive phase will likely need bigger adjustments. Instead of being off by 100 to 200 calories, you might be off by 400 to 500. You will spend more time experimenting with intake until your weight stabilizes.

The bottom line: Measured numbers are better, but a guess is not a deal breaker. The power is in the test drive and custom tune up. Those steps will correct early inaccuracies. You may just need more patience and a few extra weeks of consistent tracking before you find your true maintenance calories.

Okay, review of Step 1. Get a body fat percentage estimate. If you have this, you are ready to move on.

Step 2: Get the initial diagnostic report (BMR for your engine)

You have to start somewhere. This is the essence of the “Same Road, Different Cars” idea. A generic manual might work for a “standard sedan”, but it cannot account for your wiring, fuel economy, or whether your engine is built for power or endurance.

For a long time, I used the Harris Benedict formula as my initial guess because it is a simple, reliable starting point. Through my experience, I learned that a more specific diagnostic gives you a better head start.

We are going to use the Katch McArdle formula. It needs one extra input, your body fat percentage, which you now have. I prefer this tool because it accounts for a key part of your engine’s power, lean body mass. A BMR that factors in muscle mass is more accurate than one that only uses weight, height, and age.

We will use your weight and your body fat percentage. I am using 200 lbs and 25 percent body fat as the example. Follow the formula: you can download a simple worksheet to do the math on paper here. 

Part A: Find your engine block size (lean body mass)

Convert your body weight to kilograms.

Your weight in kg: Take your weight in pounds and multiply it by 0.4536.

For our example: 200 lbs×0.4536=90.7 kg

Next, find your Lean Body Mass, which is your total weight minus the weight of your fat. Use your body fat percentage.

Your Lean Body Mass:

For our example, with a body fat percentage of 25 percent: Lean Body Mass=90.7 kg×(1−0.25)=90.7 kg×0.75=68 kg

Your engine block weighs 68 kg. This is the core number for the next step.

Part B: Find your initial BMR

Now that you have your Lean Body Mass, use the BMR formula to find your engine’s resting power.

The formula: BMR=370+(21.6×Lean Body Mass)

Apply it to our example.

Multiply your LBM by 21.6. This number reflects the calories your muscle tissue burns at rest.

21.6×68 kg=1468.8

Add 370. The 370 is a constant that represents baseline energy needs separate from muscle mass.

370+1468.8=1838.8

Based on this initial diagnostic, your resting power is approximately 1839 calories per day. This is the best guess number you will use to begin the calibration process.

Step 3: Calculate your starting fuel budget, TDEE

Your BMR is the energy your body burns at complete rest, your engine’s idle speed. You do not spend your day idling. You are driving.

The number you need for tracking is your Total Daily Energy Expenditure, or TDEE. This is the total fuel your body needs each day for everything you do, from sleeping to exercising. Think of it as the daily fuel budget for your car. This is the number you will track in the next step.

To get this number, take the initial BMR you calculated in Step 2 and multiply it by an activity factor.

Sedentary, little to no exercise: BMR × 1.2
Lightly active, light exercise 1 to 3 days per week: BMR × 1.375
Moderately active, moderate exercise 3 to 5 days per week: BMR × 1.55
Very active, hard exercise 6 to 7 days per week: BMR × 1.725
Extra active, very hard exercise or a physical job: BMR × 1.9

For our example person with a BMR of 1839 calories, assume they are sedentary.

Their starting TDEE would be: 1839×1.2=2206.8

They would begin their tracking by eating around 2,207 calories per day. This is the number you will use for your own test drive to see how your body responds.

Step 4: Take your engine for a test drive (BMR testing)

This is where the real work, and the real learning, begins. For a few weeks, drive your car and monitor the fuel.

Fill the tank accurately: Using the TDEE number from Step 3, eat at that number of calories. This is your maintenance target. The goal is to keep the car running without gaining or losing weight.

Track your fuel: Use a food scale to measure your food and a tracking app to log every calorie. This is the crucial step. It is the only way to know how much fuel you are putting into your engine.

Check all the gauges: Look beyond the scale. Watch the whole dashboard.

The speedometer, your weight: Is your weight staying the same. If you are gaining or losing, your initial TDEE guess was off.

The engine temperature gauge, stress and mood: Are you unusually stressed, irritable, or moody. This can be a sign of metabolic stress, which affects fuel efficiency. A stressed engine is a less efficient engine.

The oil pressure gauge, sleep and energy: Are you tired and sluggish. Sleeping poorly. That is your engine light. Poor sleep and low energy can mean you are not getting enough fuel and can slow your metabolism.

Step 5: Perform the custom tune up

After a few weeks, you could have enough information to get the real numbers for your engine. For some it could take longer. For me personally? It took several months.

If your weight was stable: The average calories you consumed each day are your true TDEE. You found a reliable fuel amount for your daily drive.

If you lost weight: Your initial TDEE was too low. Your engine is more efficient than you thought. Increase daily calories slowly, for example by 100 to 200 calories, until your weight stabilizes.

If you gained weight: Your initial TDEE was too high. Your engine is conserving more than you thought. Decrease daily calories slowly until your weight stabilizes.

Once you find the number that keeps your weight stable, you have your true, custom TDEE. It is more powerful than any calculator because it is based on real world performance.

Step 6: Get your custom BMR number

Once you have completed your test drive and found the calories that keep your weight stable, your true TDEE, you can work backward to find your custom BMR.

Find your true TDEE. This is your average daily intake that kept your weight stable during the test drive.

For our example, the sedentary person found their true TDEE was 2,207 calories.

Recall your activity multiplier. This is the number you used to get your initial TDEE guess.

For our example, the activity multiplier was 1.2 for sedentary.

Divide your true TDEE by your activity multiplier. This gives your final, custom BMR.

Custom BMR = (Your True TDEE) ÷ (Your Activity Multiplier)

2207÷1.2=1839.16

Your custom BMR is approximately 1839 calories. This is your engine’s true idle speed, validated by performance on the road. It accounts for your metabolism, genetics, sleep, and stress, all of which showed up during the test drive. This is the only way to find your true BMR without a clinical lab test.

Okay, Athena, now what

This is the exciting part. You have completed a really frustrating part of any weight loss journey, finding your true numbers. Now you can move forward with confidence and a strategy.

Now that you have your numbers, the path to weight loss

You now know your fuel budget to maintain your current weight. That number is your true TDEE. It is the calories out side of the classic “calories in, calories out” equation.

Most people fail here because their calories out is a wild guess from a generic calculator. Yours is a known quantity, validated by how your body actually performs.

To lose weight, create a calorie deficit. Think of it as putting slightly less fuel in the car than it needs so it dips into reserves, your body fat, to make up the difference.

Find your calorie deficit: A safe and sustainable deficit for most people is 250 to 500 calories per day. This typically results in a loss of 0.5 to 1 pound per week, a pace that avoids shocking the engine and slowing metabolism.

Use our sedentary example with a true TDEE of 2,207 calories.

Starting TDEE: 2,207 calories
Weight loss deficit: Choose a modest deficit of 300 calories.
Daily calorie target for weight loss: 2207−300=1907 calories

Your new daily target for weight loss is 1,907 calories. This is the number you will now track.

you’re ready…

With this small, informed adjustment, you are no longer spinning your tires. You are making a precise correction that has a high probability of success and you’re giving yourself a real chance because you took the time to understand your engine.

You have the map, the numbers, and the tools. The only thing left is to keep driving and adjusting as you go. Trust the process, stay curious about what your body tells you, and remember, you are in the driver’s seat now. 

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