Health & Fitness Calculators

BMI, ideal weight and body fat: which number to use

BMI is the quickest screen, but it only uses height and weight. The BMI Calculator shows both the standard WHO categories and the lower Asian cut-offs, where 23 marks increased risk and 27.5 high risk, because South Asian, Chinese and other Asian populations tend to carry more body fat at the same BMI. If your family is from Pakistan, India, Bangladesh or the Gulf region's South Asian community, the Asian cut-offs are the more relevant guide. It also shows waist-to-height ratio, which picks up fat around the middle that BMI misses.

The Ideal Weight Calculator compares four published formulas (Devine, Robinson, Miller and Hamwi) with your healthy BMI range. They disagree by several kilos, which is a useful reminder that ideal weight is a range, not a number.

If you train with weights, BMI can label a muscular person overweight. The Body Fat Calculator uses the US Navy tape-measure method to estimate body fat percentage and lean mass, which tells you more about body composition than weight alone.

In practice, use them together. BMI and waist-to-height ratio give a quick risk screen, body fat shows composition, and the ideal weight range gives a realistic target. If they point in different directions, that is a good question to take to your doctor.

Calories and pregnancy dates

The Calorie Calculator estimates your BMR and total daily energy expenditure (TDEE) with the Mifflin-St Jeor equation, then suggests intakes to lose or gain weight at a safe pace, with macro splits. Treat the result as a starting point: track your weight for two or three weeks and adjust, because real energy use varies from person to person.

The Pregnancy Due Date Calculator works from the first day of your last period, a known conception date or an IVF transfer date, and shows how many weeks pregnant you are and key milestones. Only a small share of babies arrive on the exact due date, and an early ultrasound dating scan is more accurate than any date calculation, so follow the date your healthcare provider gives you.

For all of these tools, accurate inputs matter more than the formula. Weigh yourself at the same time of day, measure height without shoes, and take tape measurements against the skin. Small errors in a waist or neck measurement can shift a body fat estimate noticeably.

What is a healthy BMI for South Asians?

Under the Asian cut-offs from the WHO expert consultation, a BMI of 23 or above indicates increased risk and 27.5 or above high risk, lower than the standard 25 and 30. The BMI Calculator shows both scales.

How many calories should I eat to lose weight?

Start from your TDEE and eat moderately below it. The Calorie Calculator estimates TDEE with the Mifflin-St Jeor equation and suggests safe deficits. If you have a medical condition or are pregnant, ask a doctor or dietitian first.

How accurate is a due date calculator?

It gives an estimate based on a typical cycle. Few babies are born on the exact date, and an early dating ultrasound is more accurate. Always use the due date your doctor or midwife confirms.

Is the US Navy body fat method accurate?

It is a reasonable estimate from tape measurements and is widely used, but it is less precise than methods like DEXA scans. Measure carefully and at the same time of day to track changes.

Why do ideal weight formulas give different answers?

Devine, Robinson, Miller and Hamwi were derived from different data and assumptions. The Ideal Weight Calculator shows all four alongside your healthy BMI range so you can see a sensible range rather than one figure.

Is this medical advice?

No. These calculators are informational only. They do not replace advice from a doctor, midwife or registered dietitian who knows your health history.