About this calculator
This pregnancy weight gain calculator estimates guideline-based weight gain ranges using pre-pregnancy BMI, current gestational age, current weight, and whether the pregnancy is singleton or twin. It is designed for educational prenatal tracking and for discussing patterns with an obstetric clinician.
The calculator does not diagnose whether a pregnancy is healthy, prescribe a diet, or replace prenatal care. Weight gain goals may need individual adjustment for teen pregnancy, severe nausea or vomiting, diabetes, hypertension, multiple pregnancy, eating-disorder history, fetal growth concerns, or a clinician-directed plan.
Uses Institute of Medicine/National Academies gestational weight gain ranges by pre-pregnancy BMI, including singleton total ranges and second/third trimester weekly rates. Twin total ranges are shown as guideline ranges and should be individualized by an obstetric clinician.
Activated — guideline-based educational estimate
Educational estimate; not a diagnosis or treatment plan.
Formula and method
Pre-pregnancy BMI is calculated as weight in kilograms divided by height in meters squared. For singleton pregnancy, the calculator maps BMI category to IOM/NAM total recommended gain ranges: underweight 28–40 lb, normal weight 25–35 lb, overweight 15–25 lb, and obesity 11–20 lb. For weeks beyond the first trimester, it estimates an expected current range using IOM/NAM second/third trimester rates after an assumed first-trimester gain of 1.1–4.4 lb. For twins, it displays total CDC/IOM ranges by BMI category and avoids a precise week-by-week target.
Frequently asked questions
How much weight should I gain during pregnancy?+
Recommended gain depends mainly on pre-pregnancy BMI and whether you are carrying one baby or twins. For singleton pregnancy, commonly used IOM/NAM ranges are 28–40 lb for underweight, 25–35 lb for normal weight, 15–25 lb for overweight, and 11–20 lb for obesity.
Does this calculator work for twins?+
Yes, it can show total recommended twin-pregnancy ranges by pre-pregnancy BMI. It does not provide a precise weekly twin target because multiple pregnancy needs individualized obstetric monitoring.
Is it bad if I am above or below the range today?+
Not necessarily. A single weight entry can be affected by scale differences, fluid, clothing, nausea, constipation, and normal day-to-day variation. Trends and fetal growth matter more than one number, so discuss concerns with your prenatal clinician.
Should I try to lose weight during pregnancy?+
Do not start weight loss, fasting, or restrictive dieting during pregnancy without clinician guidance. If you are losing weight because of vomiting, poor intake, or illness, contact your prenatal care team.
What if my doctor gave me a different weight gain goal?+
Follow your clinician’s plan. This calculator uses population guideline ranges, while your clinician may adjust goals based on your health, fetal growth, symptoms, pregnancy type, and medical history.