HEALTH · PREGNANCY WEIGHT GAIN
Pregnancy Weight Gain Calculator
Calculate your recommended pregnancy weight gain range by pre-pregnancy BMI using IOM 2009 guidelines. Track how much weight gain is expected each week.
Below expected range for week 20 (3.6–7.9 lb).
IOM 2009 guidelines. Week-by-week tracking is approximate — consult your healthcare provider for personalized guidance.
About This Calculator
How much weight should you gain during pregnancy? The answer depends on your pre-pregnancy body mass index (BMI). The Institute of Medicine (IOM, now the National Academies of Sciences) published evidence-based guidelines in 2009 that remain the clinical standard in the United States. This calculator uses those guidelines to show your total recommended gain range and the weekly rate for your second and third trimesters.
How It Works
Enter your pre-pregnancy height and weight. The calculator computes your BMI and places you in one of four IOM categories (underweight, normal, overweight, or obese). You can also enter your current gestational age in weeks and your weight gained so far to see whether you are on track, below, or above the expected range for this point in pregnancy.
The Formula
BMI = weight (kg) / height (m)²
- BMI
- pre-pregnancy body mass index (kg/m²)
- IOM range
- total recommended gain (lb) by BMI category (IOM 2009)
- weekly rate
- lb/wk for the 2nd and 3rd trimesters by BMI category
Frequently Asked Questions
- How much weight should I gain if I was at a normal weight before pregnancy?
- The IOM 2009 guidelines recommend 25–35 lb total for those with a normal pre-pregnancy BMI (18.5–24.9). In the second and third trimesters the typical rate is about 0.35–0.50 lb per week. First-trimester gain is small — roughly 1–4 lb for most people.
- Do twins or multiple pregnancies change the recommendation?
- Yes. The IOM 2009 guidelines include separate recommendations for twin pregnancies. For normal-weight mothers of twins, the suggested range is 37–54 lb. This calculator covers singleton pregnancies only; consult your provider if you are carrying multiples.
- Is the weekly gain target the same for every week?
- No. The IOM 2009 guidelines state that first-trimester gain is small (roughly 1–4.4 lb total) for most BMI categories, with the weekly rate applying mainly to the second and third trimesters. The calculator uses this two-phase model to estimate expected gain at any given week. Individual variation is normal — your provider will guide you based on your full clinical picture.