BMR Reference for Age 21
Basal metabolic rate at age 21 is not one number — it is a range set by height and weight. This page holds the formula inputs steady at age 21 and sweeps body composition instead: four BMI levels, men at 175 cm and women at 165 cm, each estimated with both Mifflin-St Jeor and Harris-Benedict so the spread between the classic equations is visible at a glance.
Held at the same 76.6 kg, the age-20 page reads 1765 kcal against the 1760 here — 5 kcal below, which is exactly the 5 kcal the Mifflin-St Jeor age term removes per birthday. Harris-Benedict sits 75 kcal higher on that row, a 4.3% band. Across the five activity levels the same body spans 2,112 to 3,344 kcal — 1,232 kcal, against just 310 kcal that the age term strips out between 18 and 80.
BMR at age 21 by body composition
| BMI | Men (175 cm) | Women (165 cm) | ||||
|---|---|---|---|---|---|---|
| Weight | Mifflin | Harris | Weight | Mifflin | Harris | |
| 20 | 61.3 kg | 1607 kcal | 1630 kcal | 54.5 kg | 1310 kcal | 1372 kcal |
| 25 | 76.6 kg | 1760 kcal | 1835 kcal | 68.1 kg | 1446 kcal | 1498 kcal |
| 30 | 91.9 kg | 1913 kcal | 2040 kcal | 81.7 kg | 1582 kcal | 1623 kcal |
| 35 | 107.2 kg | 2066 kcal | 2245 kcal | 95.3 kg | 1718 kcal | 1749 kcal |
From BMR to daily burn: TDEE at age 21
Multiplying BMR by an activity factor gives total daily energy expenditure. The factors below are the same five levels the main calculator offers, applied to the BMI-25 man from the table (76.6 kg, BMR 1760 kcal):
| Activity level | Factor | TDEE |
|---|---|---|
| Sedentary — little or no exercise | ×1.2 | 2112 kcal/day |
| Lightly active — 1–3 days/week | ×1.375 | 2420 kcal/day |
| Moderately active — 3–5 days/week | ×1.55 | 2728 kcal/day |
| Very active — 6–7 days/week | ×1.725 | 3036 kcal/day |
| Extra active — intense daily training | ×1.9 | 3344 kcal/day |
Get your own figure
Body size matters more than any reference table can capture, so a two-minute personal estimate is usually worth more than a row of averages. Enter your numbers and the box computes the Mifflin-St Jeor result with the same coefficients used across this site:
Frequently asked questions
What is the BMR of a 21-year-old?
It depends on body size as well as age. At age 21, a 175 cm man weighing about 76.6 kg has a Mifflin-St Jeor BMR of roughly 1760 kcal per day, while a 165 cm woman at 68.1 kg lands near 1446 kcal per day. The table above shows how the estimate moves across four common body-composition levels.
Why does BMR fall as age increases?
The Mifflin-St Jeor equation subtracts 5 kcal for every year of age, so between age 20 and age 80 the estimate drops by about 300 kcal per day at the same height and weight. The coefficient is a population average: body composition, not the birthday itself, drives most of the real change.
Mifflin-St Jeor or Harris-Benedict — which should I use?
Mifflin-St Jeor is the default on this site because validation studies found it tracks measured resting energy expenditure more closely for most adults. Harris-Benedict, shown beside it in the table, runs higher for many people — often by 5 to 10 percent — so comparing the two columns is a quick way to see the uncertainty band around any single number.
Nearby ages
Want the full picture — Katch-McArdle from body-fat percentage, the age chart and TDEE in one run? Open the BMRScope calculator or browse every age page.