Mifflin-St Jeor BMR calculator
Get the modern clinical estimate of your resting calorie floor: with Mifflin-St Jeor, a 30-year-old man of 80 kg and 180 cm burns 1780 kcal a day at complete rest. Add your activity on top for a full budget. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Weight
- 80
- Height
- 180
- Age in whole years
- 30
- Sex
- Male
- Bmr kcal day
- 1,780 kcal/day
- Equation
- mifflin_st_jeor
- Weight (kg)
- 80
- Height (cm)
- 180
Basal metabolic rate is the energy your body burns at complete rest to keep vital systems running—breathing, circulation, cell repair and temperature control. The Mifflin-St Jeor equation is the modern clinical standard for estimating that daily calorie floor from four easy measurements: weight in kilograms, height in centimeters, age in years and biological sex.
What Mifflin-St Jeor computes and why it matters
Mifflin-St Jeor estimates basal metabolic rate in kilocalories per day from body mass, stature, chronological age and sex. For men the formula is ten times weight in kilograms plus six point two five times height in centimeters minus five times age plus five. For women the same weight, height and age terms apply, but the sex constant is minus one hundred sixty-one instead of plus five.
Those constants capture average differences in lean mass and resting expenditure observed in validation cohorts. The result is a resting energy floor, not total daily energy expenditure: it does not add exercise, NEAT, thermic effect of food or illness-related demand. Clinicians, dietitians and product teams still start here because the equation is widely cited, easy to audit and more accurate on average than older Harris-Benedict tables for contemporary adults.
Use the number as a baseline, then layer activity factors or measured intake data when you need a full calorie budget.
Where it fits in real health and product workflows
Nutrition coaching apps collect onboarding anthropometrics and need a defensible resting calorie number before suggesting macros. Clinical research coordinators batch-convert study-subject measurements into BMR for secondary analysis without spreading spreadsheet formulas that diverge by cell. Fitness platforms show members a transparent baseline next to wearable burn estimates so users understand the floor versus the daily total.
Insurance and employer wellness portals can pre-fill educational calculators without shipping proprietary engines. The browser path is free for single checks: enter eighty kilograms, one hundred eighty centimeters, age thirty, male, and confirm the classic one thousand seven hundred eighty kcal per day result.
What you can do with it
Onboarding calorie baselines
Convert weight, height, age and sex collected at signup into a Mifflin-St Jeor BMR before building a meal plan.
Wellness product transparency
Show users the exact BMR equation and kcal/day figure next to activity-adjusted totals in fitness dashboards.
FAQ
What does it cost?
The same calculation runs free in your browser on this page.
Which units does the formula expect?
Weight in kilograms, height in centimeters, age in years. Convert from pounds or inches before calling.
Is this total daily energy expenditure (TDEE)?
No. This returns basal metabolic rate only. Multiply by an activity factor yourself if you need estimated TDEE.
Why was my request rejected?
Weight and height must be positive numbers. Age must be non-negative and at most 130. Sex must be male or female (or m/f/man/woman).
How does Mifflin-St Jeor differ from Harris-Benedict?
Mifflin-St Jeor uses different coefficients and sex constants and is generally preferred for contemporary adults. This capability implements Mifflin-St Jeor only.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/bmr-mifflin \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"weight":80,"height":180,"age":30,"sex":"male"}'const res = await fetch("https://api.kit.forhosting.com/health/bmr-mifflin", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/bmr-mifflin",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/bmr-mifflin", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"weight":80,"height":180,"age":30,"sex":"male"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"weight":80,"height":180,"age":30,"sex":"male"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/bmr-mifflin", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"weight": 80,
"height": 180,
"age": 30,
"sex": "male"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.bmr_mifflin",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
This capability applies the formula exactly, with no fitness-tracker guesswork, no third-party nutrition API and no hidden activity multipliers.
How to call the API and interpret the fields
Send four required fields: weight as a positive number in kilograms, height as a positive number in centimeters, age as a non-negative number of years, and sex as male or female (short forms m, f, man and woman are accepted). There is no network hop, model call or randomness, so latency stays in the pure edge-parse band. Pair this result with your own activity multiplier (for example 1.2 sedentary through 1.9 very active) if you need estimated TDEE; this capability deliberately stops at BMR so product copy and clinical tools stay honest about what was measured. Aliases such as weight_kg, height_cm, kg, cm, years and gender map to the same parameters so existing forms wire in without renaming. Non-positive weight or height fail immediately with invalid_input and are not charged; missing or unparseable sex or age also raise invalid_input with a clear field name. A successful response returns bmr_kcal_day rounded to two decimal places, the normalized sex, the numeric inputs used, the sex_constant applied, a human-readable formula string and the unit label kcal/day.
Where it fits in real health and product workflows
Developers embed the call in CRON jobs and webhooks so every service shares one definition of Mifflin-St Jeor instead of reimplementing float-sensitive multiplies that disagree on rounding. The API path costs $0.002 per successful request and is billed per item, which keeps bulk onboarding scripts cheap while still covering edge execution.
Integration use cases
Clinical and research pipelines
Batch-compute resting energy estimates for study subjects with a single audited formula and stable JSON output.