Health Tools

Life expectancy has doubled since 1800 — mostly by reducing childhood death, not by people living longer in old age. Here's why historical lifespans weren't as short as averages suggest, what Blue Zones research shows, and the growing gap between total life expectancy and healthy life expectancy.

Learn how ideal body weight is calculated using the Devine, Hamwi, and Robinson formulas, what the estimates mean in practice, and their limitations for real-world weight goal setting.

Women's essential fat minimum (10-13%) is so much higher than men's (3-5%) not because of reserves or fitness level, but because the sex-specific fat deposits involved in reproductive hormone synthesis and neurological function require it. Here's the essential vs storage fat distinction, why visceral fat location matters more than total body fat percentage for metabolic health, why "athletic" body fat isn't necessarily optimal for non-athletes, and the body recomposition tracking paradox.

The ideal body weight formulas in most calculators were developed in the 1960s–70s for drug dosing — not for health or fitness goals. Here's what they actually measure, why they disagree, and what a more useful framework looks like.

Learn how to convert height between feet/inches and centimetres, with a quick reference table, real examples for medical forms and clothing sizes, and a free height converter tool.

Learn how daily water intake needs are calculated, why the 8-glasses rule falls short, how climate and activity affect hydration, and how to use a free water intake calculator for a personalised target.

"33 years, 9 months, 21 days" sounds precise — but because months have different lengths, the algorithm used to calculate the "months and days" portion involves a genuine implementation choice that can produce different results for the same two dates. Here's how the year/month/day "borrowing" algorithm works, why February 29th birthdays create a recurring ambiguity with real legal implications, and why "months" as a unit is inherently approximate.

BMI is a useful population-level tool that's routinely misapplied to individuals. Here's what it genuinely measures, where it fails, and which complementary measures give a more accurate picture of metabolic health.

Protein is the macro where most people fall short of the evidence-backed optimal amount. Here's how much you actually need, why leucine triggers muscle protein synthesis, and which foods deliver protein most efficiently per calorie.

"Drink more water" advice has a limit — exercise-associated hyponatraemia, caused by drinking more fluid than you lose during prolonged exercise, has caused documented fatalities in endurance events. Here's why thirst-based drinking is now generally preferred over fixed schedules, who's at higher risk, and what role sodium intake actually plays.