Why age matters in health calculators
Age isn't just a number when it comes to metabolism. The Mifflin-St Jeor equation used in the TDEE and macro calculators includes age because metabolism slows roughly 1–2% per decade after 20. Heart rate zones use maximum heart rate (220 − age) as their anchor. Even protein needs shift with age — older adults generally need more to prevent muscle loss.
FAQs
Does this account for leap years?
Yes — the calculation handles leap years correctly, giving you a precise count of years, months and days.
What's the difference between chronological and biological age?
Chronological age is time since birth. Biological age is how old your body actually functions — it can be younger or older depending on lifestyle, fitness, sleep, and genetics.