Pregnancy Weight Gain Calculator
Calculate the IOM-recommended total pregnancy weight gain range based on your pre-pregnancy BMI.
Most of a healthy 13.8 kg gain builds up in the second and third trimester, not the first — this shows a typical week-by-week pace for the "Normal weight" category.
- Pre-Pregnancy BMI23.6
- CategoryNormal weight
Based on Institute of Medicine (IOM) guidelines for a single pregnancy — twins/multiples have higher targets. Always follow your provider's specific guidance.
About the Pregnancy Weight Gain Calculator
Weight gain guidance during pregnancy isn't one-size-fits-all — how much is considered healthy depends heavily on the weight you started at. This calculator takes your pre-pregnancy height and weight, works out your pre-pregnancy BMI category, and returns the Institute of Medicine (IOM)'s recommended total gain range for that category, plus a rough week-by-week pacing curve.
These ranges are population-level guidelines, not a target you need to hit exactly. Real pregnancies vary — nausea, appetite changes, activity level, and the pregnancy itself (twins gain differently than a single baby) all move the number, and a provider tracking your specific pregnancy is a better authority than any calculator on what's healthy for you.
It's mainly useful early on, when you're trying to understand what a 'normal' trajectory even looks like, or partway through when you want to sanity-check whether your gain so far is roughly on pace — without having to dig up the IOM tables yourself.
Pre-pregnancy weight is sensitive information a lot of people would rather not type into a random web form. This one never leaves your device — no account, no server, no record of what you entered.
How it’s calculated
The IOM bases its recommended range on your pre-pregnancy BMI category — underweight, normal weight, overweight, or obese — because starting from a higher or lower BMI changes how much additional weight is considered healthy for both parent and baby.
The week-by-week curve isn't linear: it assumes most of the gain happens in the second and third trimester rather than the first, since first-trimester gain is typically minimal (sometimes even a loss, if nausea is significant) and the pace usually picks up notably after week 13.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI — the IOM recommends roughly 25-35 lb (11.5-16 kg) for a normal-weight BMI, more for underweight, and less for overweight or obese starting points, all for a single pregnancy.
Is it normal to gain weight unevenly across pregnancy?
Yes — most people gain very little in the first trimester and gain faster through the second and third, so a flat month-by-month pace isn't the expected pattern.
Do twins change the recommended weight gain range?
Yes, considerably — multiples come with higher IOM-recommended ranges than this single-pregnancy calculator shows, so treat this tool as inapplicable if you're carrying more than one baby and ask your provider for the multiples-specific range.
What if I'm gaining more or less than the recommended range?
A single measurement outside the range isn't automatically a problem — trends over time matter more than any one weigh-in, and your prenatal provider is best placed to say whether your specific pattern needs attention.
Does pre-pregnancy BMI actually matter for a healthy pregnancy?
It's one factor providers use to individualize weight-gain guidance, since both too little and too much gain relative to starting BMI are associated with different pregnancy risks — it isn't the only factor, but it's why the recommended range isn't the same for everyone.
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