Let me break this down so simply that even someone who has never counted a calorie in their life can follow it. Because once these numbers click, everything else in nutrition becomes straightforward math. It really is THAT simple! I want you to trust me on that 🙏🏼

What is BMR and why does it matter?

BMR stands for Basal Metabolic Rate. It is the number of calories your body burns just to keep you alive. No exercise. No walking. No activity of any kind. Just breathing, your heart beating, your organs functioning, your body maintaining its temperature.

Think of it like the fuel your car burns just sitting in the driveway with the engine running. You have not gone anywhere yet. That is your BMR.

Knowing your BMR matters because it is the foundation of every calorie target you will ever set. Without it you are guessing. With it you have a real baseline to work from.

How is BMR calculated?

The most widely used and accurate formula is called the Mifflin-St Jeor equation. Here it is:

For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5

For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161

The only difference between the two formulas is the final constant. Men add 5, women subtract 161. Everything else is identical.

Why is the constant different for men and women? It comes down to biology. On average, male bodies carry more muscle mass and less body fat than female bodies at the same height and weight. Muscle burns significantly more calories at rest than fat does. Add in hormonal differences, testosterone vs oestrogen, and the fact that men tend to have larger organs like the heart and liver which are metabolically expensive to run, and you get a meaningfully higher resting burn on average. The 166 calorie gap between the two constants reflects that difference at a population level. Individual variation within each sex can be just as large, which is why your real world results over time matter more than any formula.

Let me plug in my actual numbers so you can see exactly how it works:

Weight: 75.3kg (as of Sunday, June 7th, 2026). Height: 185cm. Age: 32 (as of Sunday, June 7th, 2026).

BMR = (10 x 75.3) + (6.25 x 185) - (5 x 32) + 5 BMR = 753 + 1,156.25 - 160 + 5 BMR = 1,754 calories per day

That is my body's baseline burn. Just existing. Nothing else. This aligns closely with what my WHOOP estimates for me at around 1,750-1,850 calories per day.

What is TDEE and how is it different?

TDEE stands for Total Daily Energy Expenditure. This is your BMR plus every single calorie you burn through activity during the day. Training, walking, steps, even the energy cost of digesting food. Everything.

TDEE is your real total calorie burn across a full day. This is the number that actually tells you how much you need to eat to maintain your current weight.

Think of it this way. Your BMR is the engine idling. Your TDEE is the engine actually driving somewhere.

How is TDEE calculated with a formula?

The traditional method takes your BMR and multiplies it by an activity factor:

Sedentary (desk job, little to no exercise): BMR x 1.2

Lightly active (1-3 days of exercise per week): BMR x 1.375

Moderately active (3-5 days per week): BMR x 1.55

Very active (hard training 6-7 days per week): BMR x 1.725

Extremely active (twice daily training, physical job): BMR x 1.9

Using my numbers, training weights 5 days per week with Zone 2 cardio after each session, one Zone 3-4 run per week, one rest day, and 10,000-12,000 steps daily as a baseline, I sit somewhere between moderately and very active.

1,754 x 1.6 (midpoint) = approximately 2,806 calories

Here is the problem. That number feels high to me and does not match what my actual results tell me. Which brings me to the more accurate approach.

How wearables measure TDEE

Devices like WHOOP, Garmin, Apple Watch and Oura track TDEE very differently from a formula. Instead of using a fixed multiplier, they measure your actual physiological data in real time and use it to estimate your true daily burn.

Here is what each major wearable actually measures:

WHOOP tracks heart rate continuously throughout the day and night, heart rate variability, respiratory rate, and skin temperature. It breaks your daily calorie burn into resting energy (your BMR equivalent) and activity strain, then combines them into your total day strain and estimated calorie burn. It also factors in your sleep quality and recovery to give you a more complete picture of what your body is doing.

Garmin uses heart rate data, VO2 max estimates, GPS movement data and your personal stats to calculate both active and resting calories separately. It is highly accurate for outdoor activities like running and cycling where GPS adds another layer of data.

Apple Watch uses heart rate, accelerometer data and your personal stats. It separates active calories from resting calories and gives you a combined total. It tends to overestimate calorie burn on certain activities, particularly strength training, because it relies heavily on movement patterns.

Oura Ring focuses more on resting and recovery metrics than active calorie burn. It is excellent for sleep tracking and HRV but less precise for high intensity training days compared to WHOOP or Garmin.

Wearables vs formulas: pros, cons and the variance between them

Formulas are useful because they give you an instant starting point with no equipment needed. The problem is they use population averages and fixed multipliers that do not account for your individual metabolism, body composition, fitness level or day to day variation. Two people with identical stats can have meaningfully different real TDEEs. A formula will give them the same number.

In my case the Mifflin-St Jeor formula with a 1.6 activity multiplier suggests around 2,800 calories. My WHOOP consistently estimates my TDEE at 2,200-2,400 calories. That is a gap of 400-600 calories per day. Over a week that is 2,800-4,200 calories of difference. If I had eaten to the formula number I would have been in a surplus the entire time while thinking I was in a deficit. That is exactly the mistake I made for years.

The variance between formulas and wearables is typically 10-20% and sometimes more. For most people the formula overestimates because the activity multipliers assume a level of intensity and consistency that most people do not actually sustain.

Wearables are more accurate because they measure what is actually happening rather than predicting from averages. The limitation is that no wearable is perfect either. Heart rate based calorie estimates can be thrown off by caffeine, stress, heat and individual heart rate variability patterns. Strength training in particular is notoriously difficult for wearables to measure accurately because heart rate does not always spike the way it does during cardio.

What is the most accurate approach overall?

Here is my honest recommendation based on what has worked for me and what the evidence supports:

Start with the Mifflin-St Jeor formula to get your ballpark / rough BMR estimate. Use a 1.4-1.6 activity multiplier to estimate your TDEE depending on your activity level. This gives you a starting number to work from.

If you have a wearable, use it as your primary TDEE reference over the formula. WHOOP and Garmin are the most accurate for active people who train consistently. Treat the wearable number as your working estimate.

Then do this regardless of which method you use: track your food intake accurately for 2-3 weeks and compare it to your weight trend. If you are eating at your estimated TDEE and your weight is dropping, your real TDEE is higher than estimated. If your weight is increasing, it is lower. Your actual results over time are the most accurate feedback mechanism available to you. More accurate than any formula and more accurate than any wearable.

This is what finally clicked for me. I was eating to a TDEE estimate I had overestimated by 400-600 calories. Once I corrected the number and started tracking accurately, the results came quickly and I stopped wondering why nothing was working.

The formula gets you close. The wearable refines it. Your results tell you the truth.

Setting your target once you have your TDEE

Cut: eat 300-500 calories below your TDEE. My training days sit at 2,050-2,100 calories. Rest days at 1,900-2,000.

Bulk: eat 300-500 calories above your TDEE. Keep the surplus controlled so you are not gaining unnecessary fat alongside the muscle.

Recomp: eat at roughly your TDEE. Progress is slower but you can lose fat and gain muscle simultaneously.

Protein stays non-negotiable throughout

Regardless of your goal, protein is the one number that does not change. I keep mine at 170-190g per day every single day. On a cut especially, adequate protein is what preserves your muscle mass and strength while you are in a deficit. Drop the protein and you lose muscle alongside the fat, which defeats the purpose.

Get your numbers right first. Then the rest is just execution over a specific time horizon based on your personal preference.

Stay locked in.

— Nik

P.s. If you’d like to follow along the journey, give me a follow on Instagram or X.