Find your Basal Metabolic Rate — the calories your body burns at complete rest.
Calculate your Basal Metabolic Rate and daily calorie needs at different activity levels.
A 30-year-old man weighing 75.0kg at 178cm has a basal metabolic rate of 1718 kcal a day — the energy used at complete rest. Moderately active, that works out to about 2662 kcal a day in total.
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What the daily total is made of
Your BMR is the floor: the energy your body uses before you move at all.
Assumptions
- Mifflin–St Jeor is used, the formula most widely recommended when body composition is unknown.
- The activity multiplier (×1.55) is a broad estimate; real expenditure varies day to day.
- Predictive equations typically land within about 10% of measured resting expenditure.
- Not medical advice; discuss any significant change in intake with a clinician.
| Goal | Daily Calories | Change/week |
|---|
| Activity | Multiplier | Calories/day |
|---|
| Formula | BMR (kcal) |
|---|
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BMR facts
- What is BMR, and how is it different from TDEE?
- BMR is the energy your body uses at complete rest. TDEE adds everything you do on top. For a moderately active 30-year-old man at 75 kg and 178 cm, that is 1718 kcal rising to 2662 kcal.
- Which formula should I use?
- Mifflin–St Jeor is the usual recommendation when body composition is unknown. If you know your body fat percentage, Katch–McArdle works from lean mass instead and is generally closer.
- How much of my daily energy is just staying alive?
- Usually most of it. At a moderate activity level, BMR is about 65% of the daily total — activity accounts for the rest.
- How accurate are these formulas?
- Predictive equations typically land within about 10% of measured resting expenditure, so treat the number as a starting point and adjust from what actually happens.
What Is BMR? Basal Metabolic Rate Explained
What is BMR?
Basal Metabolic Rate is the calories your body burns at complete rest — lying still, awake, having fasted for 12 hours, in a temperature-controlled environment. It covers energy for the heart, lungs, kidneys, liver, brain, and cellular repair. For most adults BMR ranges from around 1,300 to 2,000 kcal per day and accounts for 60–75% of total daily calorie burn.
How the three formulas differ
Mifflin–St Jeor (1990) uses weight, height, age, and sex and is the most accurate for the general population (error ±10%). Harris-Benedict (revised 1984) uses the same inputs but slightly different coefficients and tends to overestimate slightly. Katch-McArdle uses lean body mass instead of total weight, making it more accurate for muscular individuals — but it requires a body fat % input to unlock.
Activity multipliers explained
Multiplying BMR by an activity factor gives your TDEE — the calories needed to maintain your current weight. The five levels used by this calculator: Sedentary (×1.2) — desk job, little movement; Lightly active (×1.375) — light exercise 1–3 days a week; Moderately active (×1.55) — moderate exercise 3–5 days; Very active (×1.725) — hard exercise 6–7 days; Extra active (×1.9) — twice-daily training or a physical job.
What affects your BMR
BMR declines by around 1–2% per decade after age 30 as muscle mass naturally decreases — muscle burns more calories at rest than fat. Males typically have a higher BMR than females of the same height and weight because of greater lean body mass. Thyroid function, genetics, body temperature, and certain medications also influence resting metabolic rate.
Worked example
Male, age 30, 75 kg, 178 cm. Mifflin–St Jeor: BMR = (10 × 75) + (6.25 × 178) − (5 × 30) + 5 = 750 + 1,112.5 − 150 + 5 = 1,807 kcal/day. Moderately active (×1.55): TDEE = 1,807 × 1.55 = 2,801 kcal/day — the calories needed to maintain current weight.
Related calculations
To turn a resting figure into a daily one you need activity: the steps calculator estimates what walking adds, and BMR vs TDEE explains how the two combine. For splitting that intake, use the macro calculator.
How to Use Your BMR for Calorie Goals and Weight Loss
Losing weight
To lose weight, eat below your TDEE. A deficit of 500 kcal per day produces roughly 0.5 kg (1 lb) per week; a 250 kcal deficit produces about 0.25 kg per week. Deficits above 750–1,000 kcal risk significant muscle loss and are hard to sustain. A rate of 0.5–1% of body weight per week is generally considered safe — the Calorie Goals table above shows exact targets for your stats.
Building muscle
Gaining muscle requires a small calorie surplus (250–500 kcal above TDEE) combined with progressive resistance training and adequate protein (1.6–2.2 g per kg of body weight). A larger surplus accelerates fat gain alongside muscle with little additional benefit. For most people, 0.5–1 kg of muscle gain per month is a realistic natural rate.
Why TDEE changes over time
As you lose weight, your BMR falls because you are carrying less mass — a common reason fat loss plateaus. Adding muscle through resistance training raises BMR over time. Prolonged calorie restriction can also trigger metabolic adaptation, where the body lowers energy output by 5–15% beyond what weight change alone explains, making further progress harder.
Accuracy and next steps
All BMR formulas are estimates derived from population averages — individual variation of ±10% is typical. Treat your TDEE as a starting point: track your weight for 2–3 weeks at that intake and adjust by 100–200 kcal in the appropriate direction based on the result. For clinical weight management or eating disorder recovery, consult a registered dietitian rather than relying on calculator estimates alone. The macro calculator translates your TDEE into protein, fat, and carbohydrate targets.
The activity multiplier trap
Selecting too high an activity level is the most common reason a calculated TDEE leads to weight gain when eaten at "maintenance." Moderately active (×1.55) genuinely requires 3–5 days of moderate-intensity exercise per week — incidental movement like walking to work or occasional shopping does not count. If unsure, choose one level lower than you think you need, eat at that figure for 2–3 weeks, and adjust by 100–200 kcal based on whether your weight moves.
How BMR changes with age
BMR falls by roughly 1–2% per decade after 30, mainly because lean muscle mass declines with age — muscle burns about three times more energy at rest than fat. This amounts to around 15–25 fewer kcal per day each decade, small on its own but cumulative over years. Hormonal changes accelerate the process: testosterone falls gradually in men from around 40; oestrogen decline at menopause can shift body composition towards fat in women. Progressive resistance training is the most effective way to offset the age-related drop in BMR.
BMR vs RMR — an important distinction
Most tools labelled "BMR calculator" — including this one — actually compute Resting Metabolic Rate (RMR). True BMR requires a strict overnight fast and 30 minutes lying still in a temperature-controlled room; RMR allows a shorter rest and produces values roughly 10–15% higher. For the practical purpose of estimating TDEE and setting calorie targets, the difference is negligible — both are multiplied by the same activity factors to produce a daily calorie goal.
Average BMR by Age and Sex
| Age group | Men | Women |
|---|---|---|
| 20–29 | 1,650–1,850 | 1,310–1,500 |
| 30–39 | 1,600–1,800 | 1,260–1,450 |
| 40–49 | 1,550–1,750 | 1,210–1,400 |
| 50–59 | 1,500–1,700 | 1,160–1,350 |
| 60–69 | 1,450–1,650 | 1,110–1,300 |
| 70+ | 1,400–1,600 | 1,060–1,250 |
Why BMR falls with age
BMR declines by roughly 1–2% per decade after age 30, primarily because lean muscle mass decreases with age (sarcopenia). Less muscle means less metabolically active tissue — the same weight at 60 requires fewer calories to maintain than at 30. Resistance training is the most effective way to slow this decline.
Why the table shows a range, not a single value
BMR at any age depends heavily on body size. The ranges above span typical adult heights (170–180 cm for men, 160–170 cm for women) at moderate body weights. A taller or heavier person at the same age will be at the upper end of the range; a shorter or lighter person at the lower end. Use the calculator above with your specific measurements for a precise figure.
Frequently Asked Questions
What is BMR and what does it measure?
Basal Metabolic Rate is the number of calories your body burns at complete rest to maintain essential functions — breathing, circulation, organ function, and cellular repair. It is the minimum energy intake required to stay alive and typically makes up 60–75% of total daily calorie expenditure.
What is the difference between BMR and TDEE?
BMR is your resting calorie burn. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to account for exercise and daily movement. TDEE is the number to use when setting calorie targets: eating at TDEE maintains weight, below it loses weight, and above it gains weight.
Which BMR formula is the most accurate?
Mifflin–St Jeor (1990) is the most accurate for the general population with an average error of around ±10%. Katch-McArdle is more accurate for lean or muscular individuals because it uses lean body mass rather than total weight — enter your body fat % in the calculator above to unlock it.
How can I increase my BMR?
The most effective way to raise BMR is to build muscle through progressive resistance training — muscle tissue burns roughly three times more calories at rest than fat tissue. Avoiding very low-calorie diets also helps, as severe restriction can trigger metabolic adaptation that lowers resting calorie burn well beyond what weight loss alone would predict.
Evidence & Methodology
How This Page Is Grounded
Method
Uses the Mifflin–St Jeor equation to estimate resting energy expenditure, then applies the selected activity factor for daily needs.
Important limitation: Population equations can differ from an individual's measured metabolism; activity factors are broad estimates.
Primary Sources
Quality Checks
Male and female equations, units and activity multipliers are checked with worked examples.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.