Pregnancy Weight Gain Calculator
Calculate how much weight you should gain during pregnancy based on your pre-pregnancy BMI. Uses the Institute of Medicine (IOM) 2009 guidelines — the current standard recommendation used by OBs and midwives.
Pre-pregnancy BMI
23.1
Normal weight (BMI 18.5–24.9)
Recommended Total Gain
11.5–16 kg
(25.4–35.3 lbs)
Recommended Weekly Rate (2nd–3rd tri)
0.35–0.5 kg/wk
(0.8–1.1 lbs/wk)
At week 20: Above expected range
Expected gain at week 20: 4.4–5.5 kg (9.8–12.1 lbs)
Still to gain to reach target: 5.5–10.0 kg in 22 weeks. Talk to your healthcare provider about your individual situation.
IOM 2009 pregnancy weight gain guidelines
The Institute of Medicine published updated gestational weight gain guidelines in 2009 that remain the most widely used clinical reference. Recommendations are stratified by pre-pregnancy BMI because women with different starting body compositions have different needs during pregnancy.
| Pre-Pregnancy BMI | Total Gain (kg) | Weekly Rate (kg/wk) |
|---|---|---|
| Underweight (< 18.5) | 12.5–18 | 0.44–0.58 |
| Normal weight (18.5–24.9) | 11.5–16 | 0.35–0.50 |
| Overweight (25–29.9) | 7–11.5 | 0.23–0.33 |
| Obese (≥ 30) | 5–9 | 0.17–0.27 |
Weekly rates apply to the 2nd and 3rd trimester. Most women gain 0.5–2 kg in the first trimester.
Why gestational weight gain matters
Both too little and too much weight gain during pregnancy carry risks. Insufficient gain is associated with preterm birth, low birth weight, and intrauterine growth restriction. Excessive gain is associated with gestational diabetes, hypertension, large-for-gestational-age babies, and difficulty losing weight postpartum.
These recommendations are population averages. Individual circumstances — including multiple pregnancies (twins, triplets), chronic conditions, height, and ethnicity — can affect what is appropriate. Always discuss your specific weight gain targets with your midwife or obstetrician.
Frequently asked questions
Do recommendations differ for twins?
Yes. IOM 2009 guidelines for twin pregnancies recommend higher total gains: 16.8–24.5 kg for normal-weight women, 14.1–22.7 kg for overweight, and 11.3–19.1 kg for obese women. This calculator covers singleton pregnancies only.
I am above the recommended range — should I diet?
Never intentionally diet to lose weight during pregnancy. The goal if you've gained more than recommended is to slow the rate of gain — not to lose weight. Caloric restriction during pregnancy can deprive your baby of essential nutrients. Talk to your healthcare provider about nutrition and physical activity appropriate for your situation.
