BMI Calculator

BMI (body mass index) is a way of checking if your weight is healthy compared to your height. For IVF patients, BMI affects hormone balance, medication response, egg and embryo quality, and live-birth rates. Both partners’ BMI matters.

BMI is calculated the same way for men and women: weight in kilograms divided by height in metres squared (kg/m²). Our calculator does the maths instantly once you enter your details.

A normal BMI (18.5 to 24.9) gives you the best chance of successful IVF using your own eggs. Implantation, clinical-pregnancy and live-birth rates are optimised, and the miscarriage risk is lower. No BMI adjustments are needed if you have a normal BMI. 

Yes. A normal BMI is optimal for semen parameters like sperm concentration, motility and DNA integrity. Both underweight and obese men can have reduced sperm quality. A 2023 systematic review confirmed that obesity significantly worsens male fertility outcomes

These groups carry metabolic health risks at lower BMIs than white populations. Our calculator adjusts the ranges accordingly, lowering the lower and upper thresholds in line with WHO ethnic-specific guidance

Yes. For a woman, being underweight can disrupt hormone balance and endometrial receptivity, lowering success rates. You may need lower medication doses and extra care during anaesthesia. Ask your doctor whether a personalised weight-gain programme is right for you

Being overweight, as a female IVF patient, can slightly reduce your chance of a live birth, raise the miscarriage risk and lower viable embryo numbers. Your clinic may adjust your protocol to try to guard against this. A 5 to 10 per cent weight reduction before treatment may help.

Many clinics delay treatment if your BMI is 35 or more (obese class 2). At this point, success rates drop sharply and anaesthesia becomes riskier. At obese class 3 (a BMI of 40+), most clinics will insist on weight reduction first. Your clinic will advise on your specific situation. 

Yes. A higher BMI can reduce egg quality, fertilisation rates and embryo quality, and raise the risk of pregnancy complications. A 2025 systematic review found that obesity significantly lowers IVF live birth rates.

Sperm DNA fragmentation can affect sperm quality. High levels can harm male fertility and negatively affect IVF success. Both underweight and obese men tend to have higher fragmentation, while a normal BMI helps keep it low.

Even a modest 5 to 10 per cent weight reduction can improve IVF outcomes for overweight women. For men, a three-month weight-loss programme can improve sperm quality in many cases. Your doctor can set a realistic, personalised target for you.

Yes. Miscarriage risk rises as BMI increases above the normal range. Overweight and obese IVF patients have higher miscarriage rates than those with a normal BMI, This is one reason why clinics encourage weight management before treatment begins.

No. BMI is one useful marker, but it doesn’t measure body composition or metabolic health. Your clinic considers it alongside hormone levels, ovarian reserve, sperm parameters and other factors when planning your IVF treatment.

Cut-offs vary. Most follow NICE guidance on overweight and obesity management, but individual clinics set their own BMI thresholds for treatment and anaesthesia safety. Always check your clinic’s specific policy.

Often, yes – though your clinic may advise weight reduction first to improve the chance of successful treatment. Some offer treatment with adjusted protocols. An honest conversation with your doctor is the best place to start. Atter all, BMI is directly linked to IVF outcomes.