Reverse BMI Calculator

What Is a Reverse BMI Calculator?

A standard BMI calculator takes your current weight and height and gives you a BMI score. A reverse BMI calculator does the opposite, it takes your height and a desired BMI score and calculates the exact weight you need to reach.

Instead of asking "what is my BMI?" it answers "what weight do I need to be?"

It is especially useful when you have a specific goal BMI in mind and want to know the actual target weight in kilograms, stone, or pounds. Rather than guessing or using rough estimates, it gives you a precise number to work towards.

How to Use This Calculator

Using the Reverse BMI Calculator takes about ten seconds:

• 1
  Enter your height in centimetres or feet and inches
• 2
  Enter your target BMI, the score you want to reach
• 3
  Select your preferred unit for the result (kg, stone, or lbs)
• 4
  Click Calculate

Your target weight appears instantly. The calculator also shows your full healthy weight range for your height based on NHS BMI guidelines, so you can see exactly where your target sits within the healthy zone.

The Reverse BMI Formula | How It Works

The standard BMI formula is:

To reverse it and find the target weight, the formula simply rearranges to:

For imperial measurements, a conversion factor of 703 is applied:

For example, if your target BMI is 22 and your height is 1.8 metres, the calculation is: 22 × (1.8 × 1.8) = 71.28 kg. That is the exact weight you would need to be to achieve a BMI of 22 at that height.

The maths is straightforward. The calculator handles it instantly so you do not need to work it out manually.

BMI Categories | Which Target Should You Aim For?

Before you pick a target BMI, it helps to know what each BMI range means. The NHS uses the following adult categories:

Your target BMI should almost always sit within the healthy weight range of 18.5 to 24.9. Setting a target below 18.5 puts you in the underweight category, which carries its own health risks including bone density loss, reduced immune function and nutritional deficiencies.

Worked Example

Say you are 5 feet 6 inches tall (167.6 cm) and your current BMI is 28. You want to reach a BMI of 22, comfortably within the healthy range.

• Height in metres: 1.676
• Target BMI: 22
• Target weight = 22 × (1.676 × 1.676) = 61.8 kg (approximately 9 stone 10 lbs)

That gives you a clear, specific number to aim for, rather than a vague goal like "lose some weight." From there, you can calculate the calorie deficit needed to reach that target at a safe, sustainable pace.

What Is a Healthy BMI Target?

According to the NHS, the healthy weight range for most adults is a BMI between 18.5 and 24.9. Individual targets may vary based on muscle mass, age, and ethnic background.

Within that range, aiming for the middle tends to give you the most room to work with. Many health professionals suggest aiming for a BMI of around 22 to 23, which sits comfortably within the healthy range and provides a buffer against natural weight fluctuations.

A BMI of exactly 18.5 or 24.9 leaves little margin. If your weight shifts slightly in either direction, you tip outside the healthy zone. Targeting 21 to 23 gives you real-world flexibility while keeping you well within a healthy range.

That said, your ideal BMI is not purely a number. Your body composition, fitness level, and personal health history all matter. The reverse BMI calculator gives you a solid starting point, your GP or a registered dietitian can help you refine it further.

UK Ethnic BMI Adjustments

Standard BMI thresholds were developed using data from white European populations. Research has since shown that people from certain ethnic backgrounds develop weight-related health risks at lower BMI levels.

Research indicates that people from South Asian, Chinese, Black African and African-Caribbean backgrounds may have a higher risk of health conditions such as type 2 diabetes at a lower BMI. The NHS suggests lower thresholds for these groups.

For example, a BMI of 23 is considered overweight rather than the standard 25.

If you are from one of these backgrounds, your healthy target BMI may be slightly lower than the standard 18.5 to 24.9 range suggests. The NHS recommends:

If this applies to you, factor it into the target BMI you enter into the calculator. Speak to your GP for personalised guidance on the most appropriate target for your background.

BMI Range | A More Flexible Approach

Rather than targeting a single BMI number, some health professionals recommend thinking in terms of a healthy weight range for your height.

For example, at 170 cm, the NHS healthy weight range (BMI 18.5 to 24.9) corresponds to a weight range of roughly 53.4 kg to 71.9 kg. Any weight within that span is medically appropriate.

This approach suits people who find a single target number too rigid, especially those whose weight naturally fluctuates with hormonal changes, training phases or seasonal habits. Setting a target range rather than a target number gives you flexibility while still keeping you on track.

Our calculator shows both: your target weight for a specific BMI and your full healthy weight range for your height.

Limitations of BMI | What It Does Not Tell You

BMI is a useful planning tool, but it has well-documented limitations. Understanding them helps you use your reverse BMI result more intelligently.

• •It does not distinguish muscle from fat. Someone with a high level of muscle mass, an athlete, a weightlifter, or a regular gym-goer, may have a BMI in the overweight range despite having a healthy or low body fat percentage. For these individuals, BMI overstates weight-related health risk.
• •It ignores where fat is stored. Visceral fat, the fat that surrounds your internal organs around the abdomen, is far more harmful than fat stored on the hips or thighs. BMI gives no information about fat distribution. Waist circumference is often a better indicator of metabolic risk than BMI alone.
• •It does not account for age. As people get older, muscle mass naturally decreases and body fat tends to increase, sometimes without any change in overall weight. An older adult with a "healthy" BMI may still carry excess fat relative to muscle.
• •It does not apply to everyone. Pregnant women, children under 18, and elite athletes should not use standard adult BMI thresholds. Children need age and sex-specific centile charts.

The healthy BMI range of 18.5 to 24.9 is associated with the lowest population-level risk of weight-related diseases including type 2 diabetes, cardiovascular disease, and several cancers, but it remains a screening tool, not a diagnostic one.

Use your reverse BMI target weight as a directional goal. Pair it with waist circumference, how you feel physically and ideally some professional input for the full picture.

What to Do Once You Know Your Target Weight

Getting your target weight from the calculator is step one. Here is how to move forward practically:

• •Work out your calorie deficit. To lose weight sustainably, you need to consume fewer calories than you burn. Use our Calorie Deficit Calculator to find the daily calorie target that will get you to your goal weight at a safe pace.
• •Track your progress over weeks, not days. Body weight fluctuates daily due to water retention, food volume, and hormonal shifts. Weigh yourself at the same time each day and track the weekly average rather than reacting to single readings.
• •Focus on body composition alongside the number. If you are doing resistance training while losing weight, you may be building muscle and losing fat simultaneously. The scales may move slowly even while your shape improves. A tape measure around your waist often tells a more honest story than the scales alone.
• •Set a realistic timeline. At a safe rate of 0.5 to 1 kg per week, reaching a target that is 10 kg away will take roughly 10 to 20 weeks. Plan for that timeframe rather than expecting fast results.

Safe Rate of Weight Loss | NHS Guidance

This is a section most reverse BMI pages skip entirely but it is crucial information for anyone using this calculator to set a weight loss goal.

The NHS commonly recommends losing no more than 0.5 kg to 1 kg, approximately 1 lb to 2 lbs, per week. Rapid dieting to hit a BMI target is rarely sustainable long-term.

Losing weight faster than this is possible but usually involves significant calorie restriction that is hard to maintain and can lead to muscle loss, nutrient deficiencies and rebound weight gain once the diet ends.

A sustainable approach looks like this:

Slower is almost always better. Losing 0.5 kg per week consistently over six months produces better long-term results than crash dieting for four weeks and regaining the weight.

If you have a significant amount of weight to lose, more than 15 to 20 kg, speaking to your GP is a good idea. NHS weight management programmes and in some cases medication, may be appropriate alongside dietary and lifestyle changes.

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