Mifflin-St Jeor equation (step-by-step)

The Mifflin-St Jeor equation estimates how many calories you burn per day at rest. It uses weight, height, age, and a small constant that differs for males and females. The output is your estimated BMR in kcal/day.

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

If you enter US units, the calculator converts to metric behind the scenes: lb → kg (divide by 2.20462) and in → cm (multiply by 2.54). Then it runs the same formula above.

Most people care about daily maintenance calories, not just BMR. To estimate that, we multiply your BMR by an activity factor:

• Sedentary: × 1.2
• Light: × 1.375
• Moderate: × 1.55
• Very active: × 1.725
• Athlete / physical job: × 1.9

Your TDEE (Total Daily Energy Expenditure) is the approximate calorie intake that would keep your weight stable over time if nothing else changes.

Examples you can copy

Examples are the fastest way to “sanity-check” your result. Here are two realistic scenarios. (Your body is not a math equation—use these as a reference, not as a diagnosis.)

• Age: 30
• Height: 180 cm
• Weight: 80 kg
• Male BMR = 10×80 + 6.25×180 − 5×30 + 5
• = 800 + 1125 − 150 + 5 = 1780 kcal/day
• TDEE (moderate) = 1780 × 1.55 ≈ 2759 kcal/day
• Cut (−15%) ≈ 2345 · Bulk (+10%) ≈ 3035

• Age: 28
• Height: 165 cm
• Weight: 62 kg
• Female BMR = 10×62 + 6.25×165 − 5×28 − 161
• = 620 + 1031.25 − 140 − 161 = 1350 kcal/day (rounded)
• TDEE (light) = 1350 × 1.375 ≈ 1856 kcal/day
• Cut (−15%) ≈ 1578 · Bulk (+10%) ≈ 2042

If your result feels wildly off, double-check units (cm vs inches, kg vs pounds) and ensure your height entry isn’t missing a digit (e.g., 175 vs 75).

What this calculator is really doing

This tool has one job: turn your inputs into a reasonable starting estimate for calorie planning. Under the hood, it follows three simple steps:

Humans enter measurements in different unit systems. The Mifflin-St Jeor equation expects metric values, so if you use US units the calculator converts: pounds to kilograms, and feet/inches to centimeters.

The equation outputs your estimated calories burned over 24 hours at rest. This is a population-based estimate, meaning it’s tuned to “typical” adults. Your real BMR can be higher or lower depending on muscle mass, hormones, and genetics.

BMR does not include movement, work, training, or even the energy cost of digesting food. To approximate “real life,” we apply an activity factor. Finally, we compute two common planning targets:

• Cut target: about 15% below TDEE (gentle deficit).
• Bulk target: about 10% above TDEE (lean surplus).

The best practice is to treat these numbers like a testable hypothesis. Track your body weight trend for 2–3 weeks, then adjust intake up or down by 100–200 calories if progress is too fast or too slow.

How to use your result for real life

The most viral part of calorie calculators is the number—but the most valuable part is what you do next. Here’s a simple way to turn your BMR/TDEE into an actual plan.

• Start near the cut target and aim for consistency, not perfection.
• Prioritize protein and fiber so the deficit is easier to stick to.
• If your weight isn’t changing after 14–21 days, reduce 100–200 kcal/day.

• Start near the bulk target and strength train progressively.
• Gain slowly. A smaller surplus often produces better long-term results.
• If you gain too quickly, drop 100–150 kcal/day and keep training.

• Use the TDEE as your anchor, but expect small day-to-day fluctuations.
• Weekly averages matter more than single days.
• Maintenance is also a “goal” and can be useful between cutting phases.

Your body adapts. As you lose weight, your estimated TDEE usually decreases. Re-run the calculator every 4–6 weeks (or after a meaningful weight change) to keep targets realistic.

Frequently Asked Questions

• Is Mifflin-St Jeor the “best” BMR formula?

  It’s one of the most commonly used equations for adults and is often considered a solid general-purpose choice. But no formula is perfect. People with unusually high or low muscle mass (bodybuilders, very elderly adults, some medical conditions) can see larger error.

• What’s the difference between BMR and TDEE?

  BMR is what you’d burn doing nothing all day. TDEE is what you burn in real life: walking, working, training, digesting food, and everything else. TDEE is usually the number you use for dieting or bulking.

• Why does sex matter in the equation?

  The equation includes a constant that differs by sex because average body composition differs at the population level. It’s not a judgment—just a mathematical adjustment to improve average prediction.

• My result feels too high (or too low). What should I do?

  First, verify your units and inputs. Then treat the result as a starting point and validate it with your real-world trend: weigh consistently (same time of day) and look at weekly averages. Adjust intake gradually.

• Should I eat below my BMR to lose weight faster?

  Extremely aggressive deficits can be difficult to sustain and may increase fatigue, irritability, and hunger. For many adults, a moderate deficit (like ~10–20% below TDEE) is more sustainable. If you’re unsure, speak with a qualified professional.

• Does this calculator account for body fat percentage?

  No. Mifflin-St Jeor uses height, weight, age, and sex. Some other models use lean mass or body fat percentage, which can be helpful if you have accurate measurements. If you want that approach, check a lean body mass tool.

• How often should I recalculate?

  Any time your weight changes meaningfully (for many people, ~5–10 lb / 2–5 kg) or every 4–6 weeks during a cut or bulk. Calorie needs are not static.