BMR Calculator
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Author: Moiz Ahmad | Digital Marketer & SEO Expert | moizblogger.com Last Updated: May 2026 | Reviewed: Yes
Free BMR Calculator — Calculate Basal Metabolic Rate Online (2026)
Before you can build a calorie plan for weight loss, gain, or maintenance, you need to know one foundational number: how many calories your body burns just staying alive. That number is your Basal Metabolic Rate — BMR.
SmallSEOToolsn’s free BMR calculator uses the most scientifically validated formula available (Mifflin-St Jeor) to calculate your BMR and TDEE — your Total Daily Energy Expenditure — based on your sex, age, height, and weight.
KEY TAKEAWAYS
- BMR is the number of calories your body burns at complete rest — just to keep your organs functioning.
- The Mifflin-St Jeor formula (2005) is the most accurate BMR calculation method for most people — used by SmallSEOToolsn.
- BMR × Activity Multiplier = TDEE (Total Daily Energy Expenditure) — your actual daily calorie need.
- To lose weight: eat 300–500 calories below TDEE. To gain: eat 300–500 above.
- Men and women have different BMR formulas — the calculator handles this automatically.
- No sign-up, no data stored, works on all devices.
What Is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns per day at complete rest — lying still, in a temperature-neutral environment, in a fasted state — just to maintain basic physiological functions: breathing, circulation, cell production, and organ function.
BMR represents approximately 60–75% of your total daily calorie expenditure. Even if you did nothing all day, your body would still burn this many calories.
The BMR Formulas: Which One Is Most Accurate?
Three major formulas have been used historically. Understanding the difference matters for choosing the most accurate result:
1. Harris-Benedict Formula (1919, revised 1984)
The original BMR formula. Still widely used but now considered less accurate than newer alternatives.
- 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)
2. Mifflin-St Jeor Formula (1990) ✅ RECOMMENDED
Published in the American Journal of Clinical Nutrition (1990), this formula is consistently shown to be more accurate than Harris-Benedict for modern populations.
- Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
SmallSEOToolsn uses Mifflin-St Jeor as the default because it produces results within 10% of measured resting metabolic rate for most people — the highest accuracy of any simple formula.
3. Katch-McArdle Formula
Uses lean body mass (LBM) rather than total body weight — more accurate for athletes and muscular individuals, but requires knowing your body fat percentage.
- BMR = 370 + (21.6 × LBM in kg)
From BMR to TDEE: Your Actual Daily Calorie Need
BMR is your resting calorie burn. Your Total Daily Energy Expenditure (TDEE) accounts for all physical activity throughout the day.
TDEE = BMR × Activity Multiplier
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little or no exercise |
| Lightly active | × 1.375 | Light exercise 1–3 days/week |
| Moderately active | × 1.55 | Moderate exercise 3–5 days/week |
| Very active | × 1.725 | Hard exercise 6–7 days/week |
| Extra active | × 1.9 | Physical job + hard daily exercise |
Example: A 30-year-old woman, 65 kg, 165 cm, moderately active:
- BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1031.25 − 150 − 161 = 1,370 calories/day
- TDEE = 1,370 × 1.55 = 2,124 calories/day
To lose ~0.5 kg per week: eat 2,124 − 500 = 1,624 calories/day
Calorie Targets by Goal
| Goal | Daily Calorie Target |
|---|---|
| Weight loss (slow, sustainable) | TDEE − 300 to 500 |
| Weight loss (faster) | TDEE − 500 to 750 |
| Maintenance | TDEE |
| Lean muscle gain | TDEE + 200 to 300 |
| Bulking (faster gain) | TDEE + 400 to 600 |
Important: Never eat below your BMR for extended periods. This triggers adaptive thermogenesis — your body lowers its metabolic rate in response to severe restriction, making further weight loss progressively harder.
BMR and Age: Why Metabolism Slows
A frequently asked question: does metabolism actually slow with age? The answer is yes — but not entirely for the reasons most people think.
Research published in Science (2021, Pontzer et al.) — one of the most comprehensive metabolic studies ever conducted — found:
- Metabolic rate is stable from ages 20 to 60 after controlling for body composition.
- The metabolism decline in older adults is largely explained by loss of lean muscle mass (sarcopenia) — not an inherent slowing of the metabolic machinery itself.
- After age 60, there is a genuine metabolic decline of approximately 0.7% per year.
Practical implication: Resistance training to preserve muscle mass is the single most effective strategy for maintaining metabolic rate as you age. The calories-in-calories-out equation doesn’t change — but muscle loss quietly reduces the “calories-out” side over time.
AI Overview Answer
What is a BMR calculator? A BMR (Basal Metabolic Rate) calculator estimates the number of calories your body burns per day at complete rest — just to keep organs functioning. Using the Mifflin-St Jeor formula (the most accurate standard method), it calculates BMR from your sex, age, height, and weight. Multiplying BMR by an activity factor gives your TDEE — your actual daily calorie need for weight management planning.
Frequently Asked Questions
Q: What is a normal BMR? A: BMR varies significantly by body size, age, and sex. A rough guide: most adult women have a BMR of 1,300–1,600 calories/day; most adult men have a BMR of 1,600–2,100 calories/day. Smaller, older, or less muscular individuals have lower BMRs.
Q: Can I eat at BMR to lose weight? A: Technically yes — since TDEE is always higher than BMR, eating at your BMR creates a calorie deficit. However, eating significantly below BMR (a “starvation diet”) is not recommended for extended periods as it risks nutrient deficiency and metabolic adaptation.
Q: Is Mifflin-St Jeor or Harris-Benedict more accurate? A: Multiple comparative studies have shown Mifflin-St Jeor to be more accurate for predicting measured resting metabolic rate in modern diverse populations. It is the preferred formula of the Academy of Nutrition and Dietetics.
Q: Why is my BMR different from an online calculator I used before? A: Different BMR calculators use different formulas (Harris-Benedict vs. Mifflin-St Jeor vs. Katch-McArdle). Results can differ by 100–200 calories/day between formulas. SmallSEOToolsn uses Mifflin-St Jeor — the current gold standard for general populations.
Conclusion
Knowing your BMR and TDEE transforms abstract nutrition advice into actionable numbers. Whether your goal is weight loss, muscle gain, or simply maintenance, SmallSEOToolsn’s free BMR calculator gives you the starting data you need — instantly, privately, and based on the most accurate formula available.
→ Enter your details above and calculate your BMR now.