What the health numbers mean
Health calculators turn a few measurements into a number that is easier to track. Each one has limits, and knowing them stops you reading too much into a single result.
BMI is weight in kilograms divided by height in metres squared. The World Health Organization bands are under 18.5 (underweight), 18.5 to 24.9 (healthy range), 25 to 29.9 (overweight) and 30 or more (obesity). BMI does not measure fat directly, so a muscular person can score as overweight while being healthy, and it is a screening number, not a diagnosis.
BMR and calories. Basal metabolic rate is the energy your body uses at rest. The Mifflin-St Jeor equation estimates it as 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then +5 for men or −161 for women. Multiplying by an activity factor, from about 1.2 for little exercise to about 1.9 for very hard training, gives total daily energy expenditure (TDEE). Eating below it tends to lose weight and above it to gain, but the figure is an average and can be off by a few hundred calories for an individual.
Body fat. The US Navy method estimates it from neck, waist and height measurements (and hip for women). It is convenient but less precise than clinical scans, so use it to follow your own trend over time rather than to compare with other people.
Pregnancy. A due date is usually estimated as 280 days (40 weeks) from the first day of the last menstrual period. Only a small share of babies arrive exactly on that date, so treat it as the middle of a window.
Running pace. Pace is time divided by distance, so a 25-minute 5 km is 5 minutes per kilometre. Use it to plan training or set a race target.
These tools are for information and are not medical advice. If a result worries you, or you are pregnant, ill or planning a major diet change, speak to a doctor or dietitian.