BMR Reference for Age 31
Basal metabolic rate at age 31 is not one number — it is a range set by height and weight. This page holds the formula inputs steady at age 31 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.
The 5 kcal-per-year age term is visible in a single comparison: at 76.6 kg this page lists 1710 kcal, while age 30 lists 1715 — 5 kcal below. The gap between Mifflin-St Jeor and Harris-Benedict on the same row is 68 kcal (4.0%), and the sedentary-to-extra-active span is 1,197 kcal against just 310 kcal of age effect across the whole adult range.
BMR at age 31 by body composition
| BMI | Men (175 cm) | Women (165 cm) | ||||
|---|---|---|---|---|---|---|
| Weight | Mifflin | Harris | Weight | Mifflin | Harris | |
| 20 | 61.3 kg | 1557 kcal | 1573 kcal | 54.5 kg | 1260 kcal | 1328 kcal |
| 25 | 76.6 kg | 1710 kcal | 1778 kcal | 68.1 kg | 1396 kcal | 1454 kcal |
| 30 | 91.9 kg | 1863 kcal | 1983 kcal | 81.7 kg | 1532 kcal | 1580 kcal |
| 35 | 107.2 kg | 2016 kcal | 2188 kcal | 95.3 kg | 1668 kcal | 1706 kcal |
From BMR to daily burn: TDEE at age 31
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 1710 kcal):
| Activity level | Factor | TDEE |
|---|---|---|
| Sedentary — little or no exercise | ×1.2 | 2052 kcal/day |
| Lightly active — 1–3 days/week | ×1.375 | 2351 kcal/day |
| Moderately active — 3–5 days/week | ×1.55 | 2651 kcal/day |
| Very active — 6–7 days/week | ×1.725 | 2950 kcal/day |
| Extra active — intense daily training | ×1.9 | 3249 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 31-year-old?
It depends on body size as well as age. At age 31, a 175 cm man weighing about 76.6 kg has a Mifflin-St Jeor BMR of roughly 1710 kcal per day, while a 165 cm woman at 68.1 kg lands near 1396 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.