Pregnancy weight gain calculator.
Enter your height and your weight before pregnancy. You will see your pre-pregnancy BMI and the total gain range the Institute of Medicine recommends for it.
This tool is educational and does not replace your midwife or doctor. Nothing you enter leaves your device.
The ranges this calculator uses
These are the 2009 Institute of Medicine (now the National Academy of Medicine) guidelines, which US obstetricians use. They are for the whole pregnancy.
| Pre-pregnancy BMI | One baby | Twins |
|---|---|---|
| Under 18.5 (underweight) | 28–40 lb · 12.5–18 kg | No guideline |
| 18.5–24.9 (healthy weight) | 25–35 lb · 11.5–16 kg | 37–54 lb · 17–25 kg |
| 25–29.9 (overweight) | 15–25 lb · 7–11.5 kg | 31–50 lb · 14–23 kg |
| 30 and over (obesity) | 11–20 lb · 5–9 kg | 25–42 lb · 11–19 kg |
How to read your result
The range is a starting point for a conversation with your midwife or doctor, not a pass or fail. The UK does not set formal targets; the NHS simply notes that most women gain 10 kg to 12.5 kg, mostly after week 20. BMI also says nothing about muscle, build or ethnicity, so your care team may advise something different.
The NHS recommends 150 minutes of moderate activity a week in pregnancy, such as walking, swimming or yoga.
Questions, answered
How much weight should I gain during pregnancy?
The US Institute of Medicine ranges depend on your BMI before pregnancy: 28 to 40 lb (12.5 to 18 kg) if underweight, 25 to 35 lb (11.5 to 16 kg) at a healthy weight, 15 to 25 lb (7 to 11.5 kg) if overweight and 11 to 20 lb (5 to 9 kg) with obesity.
How much weight do most women gain?
The NHS says most pregnant women gain between 10 kg and 12.5 kg (22 lb to 28 lb), putting on most of the weight after week 20.
How much should I gain with twins?
The Institute of Medicine's provisional ranges for twins are 37 to 54 lb (17 to 25 kg) at a healthy pre-pregnancy weight, 31 to 50 lb (14 to 23 kg) if overweight and 25 to 42 lb (11 to 19 kg) with obesity.
Should I diet while pregnant?
Do not try to lose weight during pregnancy unless your doctor or midwife has advised it. The ranges are a guide for a conversation with them, not a target to hit on your own.
Where does the weight go?
Much of it is not fat. It includes the baby, the placenta, amniotic fluid, a larger womb and breasts, and extra blood and fluid.
Sources
- Institute of Medicine (2009): Weight Gain During Pregnancy: Reexamining the Guidelines
- MedlinePlus (US National Library of Medicine): Managing your weight gain during pregnancy
- NHS: Weight gain in pregnancy
Sources last checked on 11 November 2026.