Pregnancy Weight Gain Calculator
See the IOM recommended pregnancy weight gain for your pre-pregnancy BMI, and roughly how much gain to expect by your current week.
How it works
pre-pregnancy BMI = weight(kg) ÷ height(m)² · IOM total-gain ranges: underweight 28–40, normal 25–35, overweight 15–25, obesity 11–20 lb.
The Institute of Medicine (now the National Academy of Medicine) 2009 guidelines base recommended pregnancy weight gain on your pre-pregnancy BMI. Most of the gain is healthy and expected — the baby, placenta, fluid, extra blood and tissue — with little in the first trimester and a steadier weekly rate through the second and third. These ranges are for a single pregnancy; twins, teens and specific health conditions differ, so your provider sets your target.
Worked example
Someone 5′5″ (1.65 m) weighing 140 lb before pregnancy has a BMI of 23.3 — normal weight — so the IOM range is 25–35 lb total. By week 20, the typical pattern suggests roughly 7–11 lb gained so far.
Frequently asked questions
Is it bad to gain outside the range?
The ranges are guidance, not strict limits, and one weigh-in isn’t the whole picture. A steady trend matters more than an exact number. Discuss any concerns — too little or too much — with your provider, who tracks the pattern over time.
How much should I gain carrying twins?
More. The IOM suggests roughly 37–54 lb for a normal-weight twin pregnancy, 31–50 lb for overweight and 25–42 lb for the obesity range; there’s no formal figure for underweight. Your provider will guide you.
I’m barely gaining in the first trimester — is that normal?
Often, yes. First-trimester gain is usually small (about 1–4 lb), and nausea can even cause a slight loss. Most weight is gained later. If you’re worried, check with your provider.
Related calculators
Estimates based on standard formulas and average cycles — every pregnancy is different. This is not medical advice; your doctor or midwife, with an ultrasound, gives the accurate dates and guidance.