Assess your BMI during pregnancy and understand recommended weight gain ranges based on IOM (Institute of Medicine) guidelines. Enter your height, current weight, pre-pregnancy weight, and gestational age to get personalized recommendations for a healthy pregnancy.
| Pre-Pregnancy BMI | Category | Recommended Total Gain (lbs) | Recommended Weekly Gain (2nd & 3rd Trimester) |
|---|---|---|---|
| < 18.5 | Underweight | 28 - 40 lbs | 1 - 1.3 lbs |
| 18.5 - 24.9 | Normal Weight | 25 - 35 lbs | 0.8 - 1 lbs |
| 25 - 29.9 | Overweight | 15 - 25 lbs | 0.5 - 0.7 lbs |
| ≥ 30 | Obese | 11 - 20 lbs | 0.4 - 0.6 lbs |
Scenario: A woman who is 165 cm (5'5") tall with a pre-pregnancy weight of 60 kg (132 lbs).
Calculation: BMI = 60 ÷ (1.65)² = 22.0
Category: Normal Weight
Recommended Gain: 25 - 35 lbs
Scenario: A woman who is 170 cm (5'7") tall with a pre-pregnancy weight of 50 kg (110 lbs).
Calculation: BMI = 50 ÷ (1.70)² = 17.3
Category: Underweight
Recommended Gain: 28 - 40 lbs
Scenario: A woman who is 160 cm (5'3") tall with a pre-pregnancy weight of 75 kg (165 lbs).
Calculation: BMI = 75 ÷ (1.60)² = 29.3
Category: Overweight
Recommended Gain: 15 - 25 lbs
Scenario: A woman who is 163 cm (5'4") tall with a pre-pregnancy weight of 90 kg (198 lbs).
Calculation: BMI = 90 ÷ (1.63)² = 33.9
Category: Obese
Recommended Gain: 11 - 20 lbs
Input your height in centimeters (cm) or feet and inches. You can switch between units using the unit selector. Your height is a fixed value used to calculate BMI for both pre-pregnancy and current assessments.
Input your weight before you became pregnant, in kilograms (kg) or pounds (lbs). This is the baseline used to calculate your pre-pregnancy BMI, which determines your IOM weight gain category.
Enter your current weight during pregnancy and how many weeks pregnant you are. This allows the calculator to compare your actual weight gain with the recommended range and track your progress.
See your pre-pregnancy BMI, BMI category, current BMI, weight gained so far, and the IOM-recommended weight gain range for your category. The step-by-step breakdown shows how each value is calculated.
BMI (Body Mass Index) is calculated using the following formula:
Where:
For weight in pounds: Weight (kg) = Weight (lbs) ÷ 2.20462
For height in feet/inches: Height (m) = (Feet × 12 + Inches) × 0.0254
The Institute of Medicine (IOM) provides evidence-based guidelines for weight gain during pregnancy based on pre-pregnancy BMI. These guidelines, updated in 2009, are widely adopted by healthcare providers to promote optimal outcomes for both mother and baby.
| Pre-Pregnancy BMI | Category | Total Weight Gain Range | Weekly Rate (2nd & 3rd Trimester) |
|---|---|---|---|
| < 18.5 | Underweight | 28 - 40 lbs (12.7 - 18.1 kg) | 1 - 1.3 lbs (0.45 - 0.59 kg) |
| 18.5 - 24.9 | Normal Weight | 25 - 35 lbs (11.3 - 15.9 kg) | 0.8 - 1 lbs (0.36 - 0.45 kg) |
| 25 - 29.9 | Overweight | 15 - 25 lbs (6.8 - 11.3 kg) | 0.5 - 0.7 lbs (0.23 - 0.32 kg) |
| ≥ 30 | Obese | 11 - 20 lbs (5 - 9.1 kg) | 0.4 - 0.6 lbs (0.18 - 0.27 kg) |
Note: These guidelines are for singleton pregnancies. Women with twin or multiple pregnancies may have different recommendations. Always consult with your healthcare provider for personalized advice.
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Your pre-pregnancy Body Mass Index (BMI) is a key health indicator calculated from your height and weight before pregnancy. It determines healthy weight gain goals throughout your pregnancy. The Institute of Medicine (IOM) uses pre-pregnancy BMI to establish evidence-based weight gain recommendations that optimize outcomes for mother and baby. Maintaining weight gain within these ranges reduces risks of gestational diabetes, preeclampsia, cesarean delivery, and abnormal birth weight.
Regular monitoring helps ensure you stay on track with IOM recommendations. In the first trimester (weeks 1-12), weight gain is typically minimal — about 1-5 lbs. The majority of weight gain occurs in the second and third trimesters, with rates varying by BMI category. Our calculator helps you compare your actual gain against evidence-based targets.
The IOM's recommendations are based on research showing that optimal birth outcomes occur within specific weight gain ranges by pre-pregnancy BMI. Women who are underweight need more gain to support fetal growth, while those overweight or obese already have energy reserves requiring less additional gain to reduce health risks.
Total pregnancy weight gain includes more than just the baby's weight. The average breakdown includes:
This explains why all pregnant women need to gain some weight — even those who start overweight. The key is gaining within the appropriate range for your BMI category.
Important Medical Disclaimer: This Pregnancy BMI Calculator is for informational and educational purposes only. It provides estimates based on IOM guidelines and should not replace professional medical advice. Every pregnancy is unique, and individual circumstances may require different weight gain targets. Always consult with your healthcare provider, obstetrician, or midwife for personalized guidance on weight gain during pregnancy. If you have concerns about your weight gain, diet, or any other aspect of your pregnancy, seek professional medical attention.