Pregnancy Weight Gain Calculator
Pick your pre-pregnancy BMI category and the week you are in. We show the weight gain that guidelines suggest by now and in total.
This calculator gives general estimates for information only. It is not medical advice and does not replace a consultation with a doctor or other qualified health professional.
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The formula
Based on Institute of Medicine (2009) guidance: total gain range by starting BMI, 1 to 4.4 lb in the first trimester, then a steady weekly rate.
The recommended ranges (one baby)
| Starting BMI | Total gain | Weekly after week 13 |
|---|---|---|
| Under 18.5 | 28 to 40 lb | 1 to 1.3 lb |
| 18.5 to 24.9 | 25 to 35 lb | 0.8 to 1 lb |
| 25 to 29.9 | 15 to 25 lb | 0.5 to 0.7 lb |
| 30 and over | 11 to 20 lb | 0.4 to 0.6 lb |
How the weight is spread
Weight gain is not only fat. It includes the baby, placenta, amniotic fluid, a bigger uterus and breasts, more blood and fluid, and some stored fat for breastfeeding. Gain is usually small in the first trimester and steadier after that.
Twins
For twins, the guidelines for starting BMI 18.5 and above are 37 to 54 lb (normal weight), 31 to 50 lb (overweight) and 25 to 42 lb (obesity). There is no official range for twins with an underweight starting BMI, so ask your midwife or doctor.
Talk to your care team
These are general guidelines. Your own plan may differ, especially with conditions such as gestational diabetes. Never try to lose weight during pregnancy unless your doctor advises it.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Normal weight (BMI 18.5 to 24.9); One baby; Current week of pregnancy (0 to 42): 20 | Expected gain by week 20: 6.6 to 11.4 lb (3 to 5.2 kg) |
| Overweight (BMI 25 to 29.9); One baby; Current week of pregnancy (0 to 42): 30 | Expected gain by week 30: 9.5 to 16.3 lb (4.3 to 7.4 kg) |
| Normal weight (BMI 18.5 to 24.9); Twins; Current week of pregnancy (0 to 42): 24 | Expected gain by week 24: 13.9 to 24.9 lb (6.3 to 11.3 kg) |
Pregnancy Weight Gain Calculator: frequently asked questions
What if I am gaining more or less than the range?
Mention it at your next check-up. Plenty of healthy pregnancies fall outside the average, and your care team looks at the full picture.
Can I rely on this result as medical advice?
No. It is a general estimate for information only. It cannot replace a check-up, and your doctor can interpret the numbers for your own situation.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026