Health & Fitness Calculators

Eight health and fitness calculators, plus a wellness guide: body mass index with imperial or metric inputs, daily calorie needs from the Mifflin-St Jeor equation, a protein, carbohydrate and fat split for a target, heart-rate training zones, sleep cycle timing, one-rep max estimates for lifting, body-fat percentage by the US Navy tape method, and a pregnancy due date. All of the maths runs in your browser and nothing you enter is stored.

Which calculator do you need?

• Checking where your weight sits. Start with the BMI calculator. Because BMI cannot tell muscle from fat, pair it with the body fat calculator, which uses neck, waist and (for women) hip measurements.
• Losing, gaining or maintaining weight. The calorie calculator estimates your daily energy expenditure; the macro calculator then divides a calorie target into protein, carbohydrate and fat.
• Training. The heart rate zone calculator gives beats-per-minute ranges for each of five zones, with the Karvonen method if you know your resting heart rate. The one-rep max calculator estimates a one-rep max from a lighter set using the Epley and Brzycki formulas, so you can set training loads without testing a true maximum.
• Sleep. The sleep cycle calculator works back from your alarm in 90-minute cycles, allowing time to fall asleep, and lists bedtimes for six, seven and a half and nine hours.
• Pregnancy. The pregnancy due date calculator estimates a due date and how far along a pregnancy is.

How to read the results

Every figure here comes from a population formula. Formulas like these describe the average person well and any one person less well: an athlete can score as overweight on BMI, the 220-minus-age rule for maximum heart rate can be wrong by a wide margin for an individual, and calorie estimates move with body composition and activity that a form cannot see. Treat each result as a starting estimate, track what actually happens for two or three weeks, and adjust.

Each calculator page explains its formula, shows a worked example and lists what it leaves out. These are screening and planning tools, not diagnoses. If a result worries you, or you are pregnant, managing a condition or taking medication, talk to a doctor or another qualified professional before acting on it.