Find your recommended total weight gain and where you should be week-by-week, based on pre-pregnancy BMI and the 2009 Institute of Medicine guidelines.
Results update live as you type.
Total recommended gain
Pre-preg BMI
23.3
BMI category
Normal
Expected by wk 20
12 – 17 lbs
Remaining
13 – 18 lbs
| BMI category | BMI range | Single | Twins |
|---|
The Formula
We first calculate your pre-pregnancy BMI (weight in kg ÷ height in m²), then match that to the IOM 2009 guideline range. For week-by-week expected gain, we use ~1–4 lbs in the first trimester, then a roughly linear path to the total target over the remaining 27 weeks.
Twins follow a separate set of recommendations from the same IOM report — they're not available for underweight mothers, who should be evaluated case-by-case by an obstetrician.
IOM 2009 Ranges
About This Tool
A pregnancy weight gain calculator turns your pre-pregnancy weight and height into a healthy gain range for your entire pregnancy — plus a week-by-week pace so you can check progress as you go.
The targets come from the Institute of Medicine (now the National Academy of Medicine) 2009 guidelines, which set ranges based on pre-pregnancy BMI. Women starting at a healthy BMI are advised to gain more than women starting overweight, because babies need fuel and fat reserves regardless of the mother's starting size.
Gaining within range is associated with better outcomes for both mother and baby — fewer complications, healthier birth weights, and easier postpartum recovery. The calculator is a planning tool, not a diagnostic one: your OB or midwife should personalise the target if you have specific medical conditions.
Live Results
Ranges update the moment you change a value.
Singles & Twins
Separate IOM ranges for singleton and twin pregnancies.
Week-By-Week
See where your weight should be at any given week.
100% Free & Private
No account needed. All maths runs in your browser.
IOM-Backed
Ranges from the 2009 National Academy of Medicine report.
Imperial & Metric
Switch between lbs/inches and kg/cm instantly.
Four inputs turn into your full healthy-gain timeline.
Use the weight you were just before becoming pregnant — not your current weight.
Combined with weight, this gives your pre-pregnancy BMI — the key input.
Twin pregnancies have separate, higher recommendations from the IOM.
Use the week number from your pregnancy or due-date calculator.
Check your actual gain against the expected by week X band — flag a big mismatch with your provider.
Re-run the calculator each prenatal visit to stay on track for the rest of pregnancy.
Everything you need to know about healthy pregnancy weight gain.
The Institute of Medicine recommends 25–35 lbs for normal-weight women (BMI 18.5–24.9), 28–40 lbs if underweight, 15–25 lbs if overweight, and 11–20 lbs if obese. Twins fall in higher ranges.
Roughly 1–4 lbs in the first trimester, then about 1 lb per week through the second and third trimesters for women starting at a normal BMI. Overweight women aim closer to 0.6 lb/week.
Gaining outside the recommended range is associated with higher risks of gestational diabetes, large-for-age babies, or low birth weight. Flag persistent over- or under-gain with your OB; they may suggest a dietitian or extra monitoring.
Roughly: baby 7–8 lbs, placenta 1–2 lbs, amniotic fluid 2 lbs, breast tissue 2 lbs, blood volume 4 lbs, fluid/uterus 4 lbs, fat stores 5–9 lbs. Totals ~25–35 lbs for a typical pregnancy.
No. Calorie needs only increase by ~340 kcal/day in the second trimester and ~450 kcal/day in the third. Quality of food matters more than quantity.
The 2009 IOM (now National Academy of Medicine) guidelines are the most widely cited in the US. WHO and most other countries use very similar BMI-based ranges, with minor regional adjustments.