Find your recommended pregnancy weight-gain range from pre-pregnancy BMI, using the IOM/NASEM guidelines for a singleton or twins.
General guidance from IOM/NASEM population ranges — not medical advice. Confirm your target with your provider.
About this tool
The Pregnancy Weight Gain Calculator gives the total weight gain recommended for your pregnancy based on your pre-pregnancy body mass index (BMI), following the Institute of Medicine (IOM/NASEM 2009) guidelines. Enter your pre-pregnancy weight and height, choose metric or imperial units, and whether you are carrying one baby or twins; everything is computed locally in your browser.
BMI = weight(kg) ÷ height(m)² sorts you into a category: underweight (BMI < 18.5), normal (18.5–24.9), overweight (25–29.9) or obese (≥ 30). For a singleton the recommended total gain is 28–40 lb (underweight), 25–35 lb (normal), 15–25 lb (overweight) and 11–20 lb (obese); twin pregnancies use the higher provisional ranges. If you enter your current week, the calculator also estimates how much you should have gained so far — roughly 1–4.5 lb in the first trimester, then a steady weekly rate for your category through the rest.
Ranges are shown in your chosen units alongside your BMI and category. These are population guidelines: your own target may differ, so treat the numbers as a starting point for a conversation with your provider.
Frequently asked questions
Which guidelines does it use?
The Institute of Medicine / National Academies (IOM/NASEM 2009) ranges, keyed to pre-pregnancy BMI. Singleton: 28–40, 25–35, 15–25 and 11–20 lb for underweight, normal, overweight and obese respectively; twins use the higher provisional ranges.
How is the by-week figure estimated?
First-trimester gain is small (about 1–4.5 lb total). After week 13 it adds a steady weekly rate that depends on your BMI category (for example roughly 1 lb/week at normal weight), so the shown 'so far' range grows with the week you enter.
Why does BMI decide the range?
The evidence links healthy outcomes to gain that scales with starting weight: people who begin underweight benefit from gaining more, while those who begin with a higher BMI need less. BMI = kg ÷ m² is the standard way to classify that starting point.
Is this medical advice?
No. It is general guidance based on population averages and does not account for your individual health, twins beyond the provisional ranges, or medical conditions. Always confirm your personal target with your doctor or midwife.