BMR Reference for Age 18
Basal metabolic rate at age 18 is not one number — it is a range set by height and weight. This page holds the formula inputs steady at age 18 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-19 page reads 1770 kcal against the 1775 here — 5 kcal above, which is exactly the 5 kcal the Mifflin-St Jeor age term removes per birthday. Harris-Benedict sits 77 kcal higher on that row, a 4.3% band. Across the five activity levels the same body spans 2,130 to 3,373 kcal — 1,243 kcal, against just 310 kcal that the age term strips out between 18 and 80.
BMR at age 18 by body composition
| BMI | Men (175 cm) | Women (165 cm) | ||||
|---|---|---|---|---|---|---|
| Weight | Mifflin | Harris | Weight | Mifflin | Harris | |
| 20 | 61.3 kg | 1622 kcal | 1647 kcal | 54.5 kg | 1325 kcal | 1385 kcal |
| 25 | 76.6 kg | 1775 kcal | 1852 kcal | 68.1 kg | 1461 kcal | 1511 kcal |
| 30 | 91.9 kg | 1928 kcal | 2057 kcal | 81.7 kg | 1597 kcal | 1636 kcal |
| 35 | 107.2 kg | 2081 kcal | 2262 kcal | 95.3 kg | 1733 kcal | 1762 kcal |
From BMR to daily burn: TDEE at age 18
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 1775 kcal):
| Activity level | Factor | TDEE |
|---|---|---|
| Sedentary — little or no exercise | ×1.2 | 2130 kcal/day |
| Lightly active — 1–3 days/week | ×1.375 | 2441 kcal/day |
| Moderately active — 3–5 days/week | ×1.55 | 2751 kcal/day |
| Very active — 6–7 days/week | ×1.725 | 3062 kcal/day |
| Extra active — intense daily training | ×1.9 | 3373 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 18-year-old?
It depends on body size as well as age. At age 18, a 175 cm man weighing about 76.6 kg has a Mifflin-St Jeor BMR of roughly 1775 kcal per day, while a 165 cm woman at 68.1 kg lands near 1461 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.