Reverse BMI Calculator

A reverse BMI calculator works backwards from the standard BMI formula to find the weight needed for a specific BMI target. THE STANDARD BMI FORMULA: BMI = Weight (kg) / Height (m)². THE REVERSE BMI FORMULA: Weight (kg) = BMI × Height (m)². For imperial units: Weight (lbs) = BMI × Height (in)² / 703. HOW IT WORKS: 1. You input your height and target BMI. 2. The calculator solves for weight. 3. You get the exact weight needed to achieve that BMI. EXAMPLE: Height: 170 cm (1.70 m). Target BMI: 22 (middle of healthy range). Weight = 22 × 1.70² = 22 × 2.89 = 63.6 kg. You need to weigh 63.6 kg (140 lbs) to have a BMI of 22 at 170 cm tall. WHY USE REVERSE BMI: Set specific, measurable weight goals. Understand what "healthy weight" means for YOUR height. Calculate how much to gain or lose. Track progress toward a concrete target.

A healthy BMI is generally between 18.5 and 24.9 according to the World Health Organization (WHO). BMI CATEGORIES: | Category | BMI Range | Health Risk |. | Severely Underweight | < 16 | High risk of health issues |. | Underweight | 16 - 18.4 | Increased risk |. | Normal Weight | 18.5 - 24.9 | Lowest health risk |. | Overweight | 25 - 29.9 | Increased risk |. | Obese Class I | 30 - 34.9 | High risk |. | Obese Class II | 35 - 39.9 | Very high risk |. | Obese Class III | ≥ 40 | Extremely high risk |. RECOMMENDED TARGET BMI: For most people: 20-23 (mid-range normal). Lower end (18.5-20): Some people naturally here. Upper end (23-24.9): Still healthy, common target. WEIGHT RANGES BY HEIGHT (Normal BMI): | Height | Healthy Weight Range |. | 160 cm (5'3") | 47 - 64 kg (104-141 lbs) |. | 170 cm (5'7") | 53 - 72 kg (118-159 lbs) |. | 180 cm (5'11") | 60 - 81 kg (132-178 lbs) |. | 190 cm (6'3") | 67 - 90 kg (147-198 lbs) |. IMPORTANT CONSIDERATIONS: BMI doesn't account for muscle mass. Athletes may have higher BMI but be healthy. Age, gender, and ethnicity affect ideal ranges. Consult healthcare providers for personalized targets.

The weight change needed to change BMI by 1 point depends on your height. The taller you are, the more weight change is needed. FORMULA: Weight change for 1 BMI point = Height (m)². WEIGHT TO LOSE/GAIN PER BMI POINT BY HEIGHT: | Height | Weight per BMI Point |. | 150 cm (4'11") | 2.25 kg (5.0 lbs) |. | 160 cm (5'3") | 2.56 kg (5.6 lbs) |. | 170 cm (5'7") | 2.89 kg (6.4 lbs) |. | 175 cm (5'9") | 3.06 kg (6.7 lbs) |. | 180 cm (5'11") | 3.24 kg (7.1 lbs) |. | 185 cm (6'1") | 3.42 kg (7.5 lbs) |. | 190 cm (6'3") | 3.61 kg (8.0 lbs) |. EXAMPLE CALCULATIONS: Person A (160 cm, BMI 28, wants BMI 24): Drop needed: 4 BMI points. Weight to lose: 4 × 2.56 kg = 10.2 kg (22.5 lbs). Person B (180 cm, BMI 28, wants BMI 24): Drop needed: 4 BMI points. Weight to lose: 4 × 3.24 kg = 13.0 kg (28.6 lbs). PRACTICAL INSIGHT: Shorter people see bigger BMI changes from small weight changes. Taller people need larger weight changes for same BMI shift. This is why weight goals should be personalized to height.

The time to reach your target weight depends on how much you need to change and the rate of safe weight loss/gain. SAFE WEIGHT CHANGE RATES: FOR WEIGHT LOSS: Recommended: 0.5 - 1 kg (1-2 lbs) per week. Maximum safe: 1 kg (2 lbs) per week. Very obese individuals: May safely lose faster initially. FOR WEIGHT GAIN: Recommended: 0.25 - 0.5 kg (0.5-1 lb) per week. Focus on muscle gain, not just any weight. Requires caloric surplus + strength training. TIME ESTIMATES FOR WEIGHT LOSS: | Weight to Lose | Time (at 0.5 kg/wk) | Time (at 1 kg/wk) |. | 5 kg (11 lbs) | 10 weeks | 5 weeks |. | 10 kg (22 lbs) | 20 weeks | 10 weeks |. | 15 kg (33 lbs) | 30 weeks | 15 weeks |. | 20 kg (44 lbs) | 40 weeks | 20 weeks |. TIME ESTIMATES FOR WEIGHT GAIN: | Weight to Gain | Time (at 0.25 kg/wk) | Time (at 0.5 kg/wk) |. | 5 kg (11 lbs) | 20 weeks | 10 weeks |. | 10 kg (22 lbs) | 40 weeks | 20 weeks |. FACTORS AFFECTING TIMELINE: Starting weight and body composition. Metabolic rate and age. Consistency with diet and exercise. Sleep quality and stress levels. Medical conditions or medications. IMPORTANT: Slow, steady progress is more sustainable. Rapid weight changes often rebound. Focus on lifestyle changes, not quick fixes.

BMI is a useful screening tool but has significant limitations that you should understand when setting weight targets. KEY LIMITATIONS OF BMI: 1. DOESN'T DISTINGUISH MUSCLE VS FAT. Muscular people: High BMI but low body fat. Example: A bodybuilder at 180 cm, 100 kg = BMI 30.9 (obese). They may actually have 10% body fat (very lean). 2. DOESN'T SHOW FAT DISTRIBUTION. Belly fat (visceral) is more dangerous. Two people with same BMI can have different health risks. Waist circumference is an important additional measure. 3. AGE AND GENDER DIFFERENCES. Women typically have more body fat than men at same BMI. Older adults may have more fat and less muscle. Children and teens need age-specific BMI charts. 4. ETHNIC VARIATIONS. Asian populations: Health risks may start at lower BMI (23+). Some ethnic groups: May be healthy at slightly higher BMI. WHO acknowledges different thresholds may be needed. 5. DOESN'T ACCOUNT FOR FRAME SIZE. People with larger bone structure. May naturally weigh more without excess fat. BETTER MEASURES TO USE ALONGSIDE BMI: Waist circumference: <102 cm (men), <88 cm (women). Waist-to-hip ratio: <0.9 (men), <0.85 (women). Body fat percentage: 10-20% (men), 20-30% (women). Blood pressure, cholesterol, blood sugar levels. BOTTOM LINE: Use BMI as ONE data point, not the only measure. Consider overall health markers. Work with healthcare providers for personalized assessment.

Setting a realistic BMI goal involves considering your body type, history, and overall health - not just picking a number. FACTORS TO CONSIDER: 1. YOUR BODY FRAME SIZE. Small frame: May do well at lower end of healthy BMI (18.5-21). Medium frame: Mid-range often ideal (21-23). Large frame: Upper healthy range may be appropriate (23-25). HOW TO ESTIMATE FRAME SIZE: Wrap thumb and finger around wrist. Touch easily = small frame. Just touch = medium frame. Don't touch = large frame. 2. YOUR WEIGHT HISTORY. Your body has a "set point" it tends to maintain. Consider your weight as a healthy young adult. Extreme dieting can disrupt metabolism. 3. YOUR ACTIVITY LEVEL AND MUSCLE MASS. Athletes: Higher BMI from muscle is fine. Sedentary: Standard BMI ranges apply. Strength trainers: May target higher BMI. 4. YOUR AGE. Under 65: Standard BMI ranges (18.5-24.9). Over 65: Slightly higher BMI (23-30) may be protective. Discuss with doctor for personalized range. GOAL-SETTING APPROACH: START CONSERVATIVELY: If BMI 32 → First target BMI 28-29. Achieve, maintain, then reassess. SET PROCESS GOALS TOO: "Exercise 3x per week" vs "Lose 20 lbs". Process goals lead to outcome goals. CONSIDER NON-SCALE VICTORIES: How clothes fit. Energy levels. Health markers (blood pressure, etc.). USE 5-10% MILESTONES: Losing 5-10% of body weight. Provides significant health benefits. More achievable than distant final goal. EXAMPLE REALISTIC PLAN: Current: BMI 30, 90 kg at 173 cm. Phase 1: Target BMI 28 (84 kg) - 6-12 months. Phase 2: Target BMI 25 (75 kg) - additional 6-12 months. Phase 3: Maintain and reassess if lower goal desired.

Yes, BMI can definitely be too low. Being underweight (BMI < 18.5) carries significant health risks that are often underestimated. HEALTH RISKS OF LOW BMI: 1. WEAKENED IMMUNE SYSTEM. Increased susceptibility to infections. Slower recovery from illness. Higher risk of complications from disease. 2. NUTRITIONAL DEFICIENCIES. Anemia (iron deficiency). Osteoporosis (calcium/vitamin D). Muscle wasting (protein deficiency). Fatigue and weakness (B vitamins). 3. FERTILITY AND HORMONAL ISSUES. Women: Irregular or stopped menstruation. Both sexes: Decreased libido. Difficulty conceiving. Complications during pregnancy. 4. BONE HEALTH. Lower bone density. Higher fracture risk. Osteoporosis at younger ages. 5. CARDIOVASCULAR CONCERNS. Low blood pressure. Heart rhythm abnormalities. Reduced heart muscle mass. 6. PSYCHOLOGICAL FACTORS. May indicate eating disorders. Depression and anxiety. Body image issues. 7. SURGICAL RISKS. Higher complication rates. Slower wound healing. Longer recovery times. WHEN LOW BMI IS A CONCERN: BMI below 18.5: Clinically underweight. BMI below 17: Moderate-severe underweight. BMI below 16: Severely underweight (high risk). WHAT TO DO IF UNDERWEIGHT: Consult a healthcare provider. Rule out underlying medical conditions. Work with a registered dietitian. Gradual weight gain is safest. Focus on nutrient-dense foods. Consider strength training for muscle mass. IMPORTANT: Some people are naturally lean and healthy at lower BMIs. The key is stable weight, good nutrition, and normal health markers.

The reverse BMI calculation is mathematically precise, but its usefulness depends on understanding what BMI can and cannot tell you. MATHEMATICAL ACCURACY: The formula Weight = BMI × Height² is exact. Given accurate height input, the calculated weight is precise. No estimation or approximation in the math. The reverse calculation is as accurate as the forward calculation. PRACTICAL ACCURACY CONSIDERATIONS: 1. HEIGHT MEASUREMENT. Must measure height correctly. Posture matters (stand straight). Time of day affects height slightly. Round to nearest centimeter is fine. 2. BMI AS A HEALTH INDICATOR. BMI is a population-level screening tool. Individual variation is significant. ~30% of "normal" BMI people may have unhealthy body fat. ~50% of "overweight" BMI people may be metabolically healthy. 3. TARGET WEIGHT VS ACTUAL HEALTH. Reaching a specific weight doesn't guarantee health. Body composition matters more than weight alone. Same BMI can mean very different body compositions. IMPROVING ACCURACY OF YOUR GOALS: MEASURE MULTIPLE METRICS: BMI: Quick screening tool. Waist circumference: Abdominal fat indicator. Body fat percentage: More accurate composition. Blood markers: Actual health indicators. USE BMI AS A GUIDE, NOT A RULE: The calculated target weight is a useful reference. Adjust based on how you feel and function. Work with healthcare providers for fine-tuning. TRACK TRENDS OVER TIME: Single measurements are snapshots. Trends tell the real story. Don't obsess over daily fluctuations. BOTTOM LINE: The math is accurate. BMI is an imperfect but useful tool. Use the calculated target as a starting point, not an absolute goal. Adjust based on real-world results and health markers.