Health & Fitness Guides

Plain-English explainers for the questions our calculators answer. Built on recognized public guidelines, with the science kept honest about its limits.

Body & weight

Understanding BMI What Body Mass Index measures, where it works, and where it badly misleads.

Fitness & lifestyle

Heart Rate Zones Explained What the five training zones mean and how to train by effort. Steps & Calories What "10,000 steps" really means and how steps turn into calories. Daily Water Intake How much water you really need — and the myth of eight glasses. Sleep Cycles Explained What happens across a night and why waking time matters.

Wellbeing

Understanding Your Cycle The phases of a typical menstrual cycle and what shifts them. Managing Everyday Stress Practical, evidence-informed steps to take the edge off.