BMR Calculator Guide: How Basal Metabolic Rate Works基础代谢率(BMR)计算器指南：BMR 是如何计算的

Most of the calories you burn each day have nothing to do with exercise. They're spent keeping you alive — your heart beating, your brain thinking, your cells regenerating, your temperature stable. That baseline is your Basal Metabolic Rate, and it typically accounts for 60% to 75% of total daily expenditure. Understanding it is the foundation of every successful diet, every accurate calorie count, and every reasonable weight-loss plan.

What Is BMR?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest in a thermoneutral environment — i.e., lying still, awake, after a 12-hour fast, at room temperature. It's the energy required to keep your organs functioning: brain, heart, liver, kidneys, lungs, and skeletal muscle.

BMR is not the same as TDEE (Total Daily Energy Expenditure). TDEE = BMR + activity calories + thermic effect of food. BMR is the floor; everything else stacks on top.

The Mifflin-St Jeor Formula

Several equations estimate BMR, but the Mifflin-St Jeor formula has been the gold standard since 1990 and is what most modern calculators use:

Worked example for a 35-year-old woman, 65 kg, 165 cm:

BMR = 10(65) + 6.25(165) − 5(35) − 161
= 650 + 1,031.25 − 175 − 161
= 1,345 calories/day

Even at complete rest — no walking, no fidgeting, no digestion — this woman burns about 1,345 calories per day. For comparison, a moderately active 35-year-old man of the same weight would burn roughly 1,700.

Why Mifflin-St Jeor Beats the Alternatives

Three older formulas are still floating around the internet:

• Harris-Benedict (1919) — overestimates BMR by 5%+ for most modern populations. Was revised in 1984 but still less accurate.
• Katch-McArdle — uses lean body mass instead of weight. More accurate if you know your body fat percentage; useless otherwise.
• Schofield — UNESCO's equation, derived from tropical populations. Tends to underestimate BMR in Western adults.

Mifflin-St Jeor is more accurate within ±10% for most adults, which is why it's the default in clinical settings.

What Affects BMR

Five factors move the number up or down:

1. Lean body mass. Muscle tissue is metabolically expensive; fat tissue isn't. Two people at the same weight can have BMRs differing by 200–300 calories based on body composition.
2. Age. BMR declines about 1%–2% per decade after age 20, mostly due to muscle loss.
3. Sex. Men typically have 5%–10% higher BMR than women at the same weight, mostly because of greater muscle mass.
4. Genetics. Some people's cells run "hotter" — there's a 20% spread in BMR between people of identical stats.
5. Hormones. Thyroid hormone is the master regulator — hyperthyroidism can raise BMR by 30%+; hypothyroidism can lower it similarly. Pregnancy raises BMR substantially.
💡 Dieting slows BMR

Long-term severe calorie restriction causes adaptive thermogenesis: BMR drops more than the formula predicts. After losing 10% of body weight, BMR may drop 15% rather than the expected 10%. This is why "calories in, calories out" isn't a complete model — your body adapts to defend its weight.

From BMR to Daily Calories

BMR alone tells you only the resting number. To estimate your total daily burn, multiply by an activity factor:

Activity level	Multiplier	Example day
Sedentary	1.2	Desk job, no exercise
Lightly active	1.375	Desk job + 1–3 workouts/week
Moderately active	1.55	Active job or 3–5 workouts/week
Very active	1.725	Physical job + daily exercise
Athlete-level	1.9	2-a-day training

For our example: 1,345 × 1.55 = ~2,085 calories/day to maintain weight at moderate activity. To lose weight, eat 300–500 calories below this; to gain, eat 300+ above.

Common BMR Mistakes

Three errors that derail most calorie-counting attempts:

• Using BMR as your daily target. BMR is the resting number. Eating at BMR level will cause weight loss, then plateau, because your TDEE is much higher. Always target TDEE minus a deficit.
• Overestimating activity. Most people think they're "moderately active" when they're actually sedentary. Be honest about how much you actually move — the difference is 400+ calories.
• Forgetting the thermic effect. Protein burns ~25% of its calories in digestion; carbs ~7%; fat ~3%. A high-protein diet modestly raises your daily burn.

Try It

Use the BMR Calculator to:

• Get your resting calorie burn from age, sex, height, and weight.
• See the difference between Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle estimates.
• Multiply by activity factors to estimate your TDEE.

For a complete daily-calorie target including activity and goals, use the companion TDEE Calculator.

你每天消耗的大部分卡路里和运动无关。它们用于维持你活着——心脏跳动、大脑思考、细胞再生、体温稳定。这个基线就是你的基础代谢率(BMR)，通常占总日消耗的 60%–75%。理解它是每个成功节食、准确卡路里计算、合理减肥计划的基础。

什么是 BMR？

BMR 是你在热中性环境中完全休息时的卡路里消耗——即静卧、清醒、空腹 12 小时后、室温下。它是维持器官运转所需的能量：脑、心、肝、肾、肺、骨骼肌。

BMR ≠ TDEE。TDEE = BMR + 活动消耗 + 食物热效应。BMR 是底线；其他都加在上面。

Mifflin-St Jeor 公式

几个公式都能估算 BMR，但 Mifflin-St Jeor 自 1990 年以来一直是金标准，也是大多数现代计算器的默认：

举例：35 岁女性、65 kg、165 cm：

BMR = 10(65) + 6.25(165) − 5(35) − 161
= 650 + 1,031.25 − 175 − 161
= 1,345 卡/天

即使完全不动——不走路、不坐立不安、不消化——这位女性每天也烧约 1,345 卡。相比之下，同体重、中等活动量的 35 岁男性约 1,700。

为什么 Mifflin-St Jeor 更准

网上还能看到三个老公式：

• Harris-Benedict(1919)——对大多数现代人高估 BMR 5%+。1984 修订过，但仍不够准。
• Katch-McArdle——用瘦体重代替总重。如果知道体脂率更准；否则无用。
• Schofield——联合国教科文组织公式，从热带人群推导。倾向低估西方成年人 BMR。

Mifflin-St Jeor 对大多数成年人误差 ±10% 内，临床默认用。

什么影响 BMR

五个因素让数字上下浮动：

1. 瘦体重。肌肉组织代谢昂贵；脂肪组织不是。同体重两人 BMR 可差 200–300 卡，取决于身体成分。
2. 年龄。20 岁后 BMR 每十年下降 1%–2%，主因是肌肉流失。
3. 性别。同体重男性 BMR 通常高 5%–10%，主因是肌肉更多。
4. 遗传。有的人细胞跑得"更热"——相同数据两人 BMR 差 20%。
5. 激素。甲状腺激素是主调节器——甲亢可提高 BMR 30%+；甲减类似降低。孕期大幅提升 BMR。

从 BMR 到每日卡路里

BMR 只告诉你休息的数字。要估算总日消耗，乘以活动系数：

活动水平	系数	举例
久坐	1.2	办公室、不运动
轻度活动	1.375	办公室 + 每周 1–3 次运动
中度活动	1.55	体力工作或每周 3–5 次运动
高度活动	1.725	体力工作 + 每日运动
运动员级	1.9	一天两练

我们的例子：1,345 × 1.55 = ~2,085 卡/天维持中度活动。减肥吃比这个少 300–500 卡；增重多 300+。

常见 BMR 误区

三个错误破坏大多数卡路里计数尝试：

• 用 BMR 当每日目标。BMR 是休息数字。按 BMR 吃会导致减肥然后平台，因为你的 TDEE 高得多。永远目标 TDEE 减缺口。
• 高估活动。多数人觉得"中度活动"实际是久坐。诚实面对你真正动了多少——差距 400+ 卡。
• 忘记食物热效应。蛋白质消化消耗约 25% 卡路里；碳水 7%；脂肪 3%。高蛋白饮食会略提升每日消耗。

动手试试

用 BMR 计算器：

• 从年龄、性别、身高、体重算休息卡路里。
• 看 Mifflin-St Jeor、Harris-Benedict、Katch-McArdle 的差异。
• 乘活动系数估算 TDEE。

要算包含活动和目标的完整每日卡路里，用配套 TDEE 计算器。