Pregnancy Weight Gain Calculator
Calculate recommended weight gain during pregnancy based on pre-pregnancy BMI and gestational week, following IOM guidelines.
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How to use this calculator
The Institute of Medicine recommends different total weight gain ranges based on pre-pregnancy BMI. Gain is minimal in the first trimester and roughly 0.3–0.5 kg/week thereafter.
- 1
Enter your pre-pregnancy weight and height to calculate your pre-pregnancy BMI.
- 2
Enter your current gestational week and current weight.
- 3
The calculator compares your actual weight gain to IOM 2009 guidelines and shows if you're on track.
Frequently asked questions
Why does pre-pregnancy BMI matter?
The amount of weight gain recommended during pregnancy varies based on your starting BMI. Underweight women need to gain more; obese women need to gain less. These ranges optimise outcomes for both mother and baby.
Is it harmful to gain too much weight during pregnancy?
Excess gestational weight gain is associated with gestational diabetes, pre-eclampsia, caesarean delivery, and higher infant birth weight. Insufficient gain is linked to preterm birth and low birth weight. Staying within recommended ranges is important for both.
Can I diet during pregnancy?
Calorie restriction diets are not recommended during pregnancy. If you are gaining faster than guidelines suggest, focus on nutrient-dense foods and light activity rather than calorie counting. Always follow your healthcare provider's personalised advice.
Pregnancy Weight Gain Calculator — IOM Guidelines
IOM 2009 pregnancy weight gain recommendations
The Institute of Medicine guidelines recommend: underweight (BMI <18.5): 12.5–18 kg; normal weight (BMI 18.5–24.9): 11.5–16 kg; overweight (BMI 25–29.9): 7–11.5 kg; obese (BMI ≥30): 5–9 kg. For twin pregnancies, recommended ranges are higher across all BMI categories.
Where does pregnancy weight gain go?
The typical 11.5–16 kg gain breaks down roughly as: baby (3–4 kg), placenta (0.7 kg), amniotic fluid (0.9 kg), uterus growth (0.9 kg), breast tissue (0.9 kg), blood volume increase (1.5 kg), extra fluid (1.8 kg), and fat stores (2.5–3.5 kg) for energy reserves and breastfeeding.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →