Calories & Energy Needs

What is a Calorie?

A calorie is simply a unit of energy — the same way a kilometer measures distance. Your body uses that energy for everything: breathing, thinking, growing, healing, and moving. Food and drink are where that energy comes from.

Why Needs Vary So Much

There's no single "correct" calorie number — it depends on age, sex, height, activity level, and importantly, whether someone is still growing:

• Kids and teens generally need more energy relative to their size than adults, not less — growth, development, and puberty all take significant energy.
• Activity level changes needs a lot — an athlete in-season and someone recovering from an injury will have very different needs even at the same age and size.
• Needs shift constantly. A number that fits this month may not fit after a growth spurt or a change in activity.

What This Number Isn't

An estimate like this is a rough starting reference, not a target to hit exactly or a restriction to stay under. Formulas like this one were built and validated on adult populations — they're even less precise for children and teenagers, whose energy needs fluctuate with growth. This page shouldn't be used to plan restrictive eating, and if you're under 18, this is genuinely something to figure out with a parent, guardian, or doctor rather than alone.

Try an Estimate

Uses the Mifflin–St Jeor equation, a widely used adult estimation formula. Treat the result as a ballpark figure, not a precise or personal recommendation.

Sources

• Dietary Guidelines for Americans (USDA/HHS)
• CDC — Healthy Weight, Nutrition, and Physical Activity

Reviewed by the Polaris Youth editorial team. Last reviewed: July 2026.