How this BMR calculator works (step by step)

The goal of a BMR calculator is simple: estimate how many calories your body would burn if you did absolutely nothing for 24 hours — basically, “alive, resting, and existing.” That number is your Basal Metabolic Rate (BMR), usually expressed in kcal/day. In everyday terms, it’s the energy cost of running your body’s “background processes”: breathing, blood flow, nervous system activity, temperature regulation, and the constant cellular repair that happens even while you sleep.

The moment you stand up, walk, think, talk, digest food, or exercise, you burn more than BMR. That’s where TDEE (Total Daily Energy Expenditure) comes in. TDEE is the “real-life” daily number most people care about because it includes movement and activity. Most calorie plans start with:

• BMR = baseline calories at rest
• TDEE = BMR × activity factor (maintenance calories)

This calculator gives you both. Choose “Resting / BMR only” if you only want BMR, or pick an activity level to convert BMR into an estimated maintenance range. The number is a starting point — your real maintenance depends on your step count, job, training, sleep, stress, and how consistently you track intake. The best use of a BMR/TDEE estimate is to start smart, then refine with real results over 2–3 weeks.

The equations are written in metric units. If you enter inches or pounds, the calculator converts them behind the scenes: cm = inches × 2.54 and kg = pounds ÷ 2.2046226218. This matters because even small unit mistakes can create big calorie differences.

You can choose between two widely used BMR equations. Mifflin–St Jeor is commonly recommended in modern diet apps because it often performs well for contemporary populations. Harris–Benedict (revised) is also popular and appears in many classic tools. Both are estimates — the “best” formula is usually the one you use consistently, so your trends are comparable over time.

Mifflin–St Jeor:

• Men: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5
• Women: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161

Harris–Benedict (revised):

• Men: BMR = 88.362 + 13.397×weight(kg) + 4.799×height(cm) − 5.677×age
• Women: BMR = 447.593 + 9.247×weight(kg) + 3.098×height(cm) − 4.330×age

Notice the variables: weight and height increase BMR (bigger body = more energy demand) while age reduces it (because, on average, people lose some lean mass and reduce movement with age). Sex matters because, on average, men carry more lean mass at the same body weight — and lean mass is metabolically active.

If you select an activity level, we multiply BMR by an activity factor. This is a standard approach used in many diet systems. It does not “know” your exact workouts — it approximates your lifestyle:

• 1.2 sedentary: desk job, little exercise
• 1.375 light: 1–3 workouts/week or lots of casual walking
• 1.55 moderate: 3–5 workouts/week
• 1.725 very active: 6–7 workouts/week or active job
• 1.9 athlete: hard training and/or very physical work

Example: if your BMR is 1,500 kcal/day and you’re moderately active, TDEE ≈ 1,500 × 1.55 = 2,325 kcal/day. That’s your “maintenance” starting point — the intake level where your weight would likely stay roughly stable. If your weight trends down over weeks, your true maintenance might be slightly higher than the estimate; if it trends up, it might be slightly lower. That feedback loop is how you turn an estimate into a personalized number.

The little “lower → higher” meter is a share-friendly visual. It’s not a medical category. It simply maps typical adult BMR ranges (roughly 1,000 to 3,000 kcal/day) so your result is easy to understand at a glance and looks good in a screenshot.

BMR examples (with real math)

These examples show what the calculator is doing. Don’t worry if your number differs — the point is to understand how changes in weight, height, sex, and age affect the result. If you want consistency for tracking, pick one formula and stick with it.

Inputs: Male, age 30, height 180 cm, weight 80 kg (Mifflin–St Jeor)

• BMR = 10×80 + 6.25×180 − 5×30 + 5
• BMR = 800 + 1,125 − 150 + 5 = 1,780 kcal/day
• If activity = 1.55, TDEE ≈ 1,780 × 1.55 = 2,759 kcal/day

Inputs: Female, age 35, height 165 cm, weight 65 kg (Mifflin–St Jeor)

• BMR = 10×65 + 6.25×165 − 5×35 − 161
• BMR = 650 + 1,031.25 − 175 − 161 = 1,345 kcal/day (rounded)
• If activity = 1.375, TDEE ≈ 1,345 × 1.375 = 1,849 kcal/day

If you switch to Harris–Benedict, you may see a different BMR. That’s normal because each equation is a different statistical model. Use the difference as context, not confusion. Many people simply use Mifflin as a default and adjust with real-life tracking.

• Maintenance: start near TDEE for 1–2 weeks; track weight trend.
• Fat loss: subtract ~250–500 kcal/day from TDEE; keep protein high.
• Muscle gain: add ~150–300 kcal/day; lift progressively.
• Refine: adjust by ~100–200 kcal/day based on weekly averages.

The “best” calorie target is the one you can follow consistently. A perfect spreadsheet plan that you can’t stick to loses to a simple plan you execute daily.

BMR vs RMR vs TDEE (quick clarity)

People often mix up BMR, RMR, and TDEE. Here’s the clean version:

• BMR: strict resting estimate (lab-style definition)
• RMR: similar to BMR but usually slightly higher in practice
• TDEE: your total daily burn including activity and digestion

This tool gives a BMR-style estimate and optionally TDEE. If you’re dieting, it’s common to start with TDEE, run the plan for 2–3 weeks, then adjust. That “measure → adjust” loop beats guesswork.

• Lean mass differences (muscle burns more at rest than fat)
• Daily steps and fidgeting vary more than people realize
• Sleep, stress, and hunger change behavior
• Food tracking errors (very common!)
• Adaptive changes during long diets

If the calculator says your maintenance is 2,200 kcal/day but you maintain at 2,000 in reality, trust reality and use the calculator as a baseline guide going forward.

Frequently Asked Questions

• What is a “good” BMR?

  There isn’t one universal “good” number. BMR depends on body size, age, sex, and lean mass. What matters is using BMR/TDEE to create a plan that matches your goal and how your body responds.

• Is BMR the same as calories needed per day?

  No. BMR is your baseline at rest. Most people need more than BMR because they move and digest food. TDEE is the better daily “maintenance” starting point.

• Which formula is most accurate?

  Mifflin–St Jeor is commonly used in modern tools and is a strong default. Harris–Benedict is also widely used. The most useful approach is consistency (pick one) and then personal adjustment using real tracking.

• Does lifting weights increase BMR?

  Building or maintaining muscle can raise resting needs slightly and improves body composition. It also increases daily burn via activity. The bigger benefit is long-term strength, health, and adherence.

• Can I use this for medical diets or pregnancy?

  Use extra caution. Pregnancy, medical conditions, and specific clinical diets change energy needs. For medical decisions, professional guidance is best.

• Why is my BMR “low” even though I work out?

  BMR depends mostly on body size and lean mass, not workouts. Training impacts TDEE and fitness, but your baseline still tracks body mass. If you’re small, your BMR will naturally be lower — that’s normal.