Find your recommended weight-gain range based on the Institute of Medicine's 2009 guidelines — the global standard. Track progress by week if you want.
Written and reviewed by the babybumpkit editorial team, drawing on IOM, ACOG, CDC, and Mayo Clinic.
How the recommendations work
The recommended total pregnancy weight-gain range depends on your pre-pregnancy BMI — not your current weight. The Institute of Medicine (IOM) published the current ranges in 2009 after re-examining decades of pregnancy outcome data. They've been adopted by ACOG, the CDC, and most international guidelines.
Singleton ranges by pre-pregnancy BMI:
Underweight (BMI < 18.5): 28–40 lb (12.5–18 kg)
Normal weight (BMI 18.5–24.9): 25–35 lb (11.5–16 kg)
Overweight (BMI 25–29.9): 15–25 lb (7–11.5 kg)
Obese (BMI ≥ 30): 11–20 lb (5–9 kg)
Lower pre-pregnancy BMI = higher recommended gain. Higher pre-pregnancy BMI = lower recommended gain. The ranges aren't about appearance — they're associated with the lowest rates of pregnancy complications and the best outcomes for both parent and baby.
First trimester vs. second and third
Pregnancy weight gain isn't linear across the whole 40 weeks. The IOM breaks it into two phases:
First trimester (weeks 1–13): total gain of just 1–4 lb (0.5–2 kg) is typical, regardless of BMI category. Many people gain very little or even lose a small amount due to morning sickness — that's normal.
Second and third trimesters (weeks 14–40): most of pregnancy weight is gained here, at a roughly steady weekly pace. For normal-BMI singleton pregnancies that's about 1 lb (0.4–0.5 kg) per week; less for overweight or obese categories, slightly more for underweight.
The calculator above shows your cumulative target at any given week so you can sanity-check progress, not just total gain at delivery.
Twin pregnancies
Twin pregnancies need more weight gain. The IOM's provisional twin ranges:
Normal weight: 37–54 lb (17–25 kg)
Overweight: 31–50 lb (14–23 kg)
Obese: 25–42 lb (11–19 kg)
The IOM didn't issue a firm range for underweight twin pregnancies; clinical literature commonly suggests 50–62 lb (23–28 kg). Triplet pregnancies need even more — work with your provider on a specific plan.
When weight gain becomes a concern
Gaining too quickly isn't automatically a problem, but it's worth raising at your next prenatal visit. Sudden gain — multiple pounds in a single week — can indicate fluid retention from pre-eclampsia, especially if paired with high blood pressure, sudden swelling in hands or face, or visual changes. Sustained over-range gain is associated with gestational diabetes, delivery complications, and a larger baby.
Gaining too slowly is normal in the first trimester (especially with morning sickness) and concerning if sustained through the second and third. Persistently low gain is associated with low birth weight and preterm birth. If you're struggling to gain, talk to your provider about calorie needs and any conditions affecting appetite or absorption.
Dieting during pregnancy isn't recommended even for those who started at a higher BMI — the IOM ranges already reflect lower targets. Focus on the quality of food (vegetables, lean protein, whole grains) and gentle consistent activity, rather than calorie restriction.
A note on body and pregnancy
Pregnancy changes bodies. The IOM ranges describe what's associated with the lowest medical risk — they aren't a standard for how you should feel about your body or what you should look like. Whatever you weigh before, during, or after pregnancy, you're not the calculator's output. Use the numbers for your provider, not for your self-image.
Frequently asked questions
The Institute of Medicine (IOM) recommends a total weight gain range based on your pre-pregnancy BMI: 28–40 lb (12.5–18 kg) if underweight, 25–35 lb (11.5–16 kg) if normal weight, 15–25 lb (7–11.5 kg) if overweight, and 11–20 lb (5–9 kg) if obese. These ranges are for singleton pregnancies; twin pregnancies have higher targets. Your provider may adjust based on your specific circumstances.
Pregnancy weight-gain BMI uses your weight before pregnancy — not your current weight. Calculate it as weight in kilograms divided by height in meters squared, or use the calculator above. BMI categories: under 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is obese. These thresholds drive the IOM gain recommendations.
People with lower pre-pregnancy BMI tend to need more gain to support a healthy pregnancy and adequate fetal growth. People with higher pre-pregnancy BMI typically have more energy reserves available, so the recommended additional gain is smaller. Both ends of the spectrum carry risks if gain is too low or too high: too little gain is associated with low birth weight; too much with gestational diabetes, hypertension, and a larger baby.
Most pregnancy weight gain happens in the second and third trimesters at roughly a consistent pace. The first trimester typically adds only about 1–4 lb (0.5–2 kg) total. From week 14 onward, average weekly gain is about 1 lb (0.5 kg) for normal-weight people, less for higher-BMI people, and slightly more for underweight people. Sudden large jumps in a single week can signal fluid retention and should be mentioned to your provider.
Gaining faster than the IOM range isn't automatically a problem, but it's worth flagging to your provider. They'll want to rule out fluid retention (which can indicate pre-eclampsia, especially with high blood pressure or sudden swelling), gestational diabetes, or larger-than-expected fetal growth. Often it's just natural variation. A sustained pace well above the range is associated with delivery complications and a higher baby birth weight.
Slow gain in the first trimester is normal — many people gain very little or even lose a small amount due to morning sickness. Sustained slow gain in the second and third trimesters is more concerning because it's associated with low birth weight and preterm birth. Talk to your provider about your nutrition, calorie intake, and any conditions (like hyperemesis or thyroid problems) that might be limiting gain.
Yes — twin pregnancies require more total gain. IOM recommendations for twins: 37–54 lb (17–25 kg) if normal weight, 31–50 lb (14–23 kg) if overweight, and 25–42 lb (11–19 kg) if obese. The IOM didn't issue a firm range for underweight twin mothers, but clinical literature commonly recommends 50–62 lb (23–28 kg). Triplet pregnancies require even more.
An average newborn weighs 7–8 lb (3.2–3.6 kg). The rest of typical pregnancy weight gain breaks down roughly as: placenta 1–2 lb, amniotic fluid 2 lb, increased blood volume 3–4 lb, increased breast tissue 1–3 lb, larger uterus 2 lb, and stored fat and protein 5–8 lb. Most of this normalizes within months postpartum, though body composition often changes long-term.
Active calorie-restriction dieting is not recommended during pregnancy, even for people who started at a higher BMI. The IOM ranges already reflect lower gains for higher BMI categories. If you're concerned about gain, focus on the quality of what you eat (vegetables, lean protein, whole grains) and consistent gentle activity, rather than cutting calories. Your provider or a registered dietitian can help tailor nutrition without restriction.
The math itself is well-established (BMI plus IOM tables), so the recommended ranges are accurate to the guideline. What the calculator can't do is account for individual variation — your provider knows your specific pregnancy and may have reasons to recommend a different target. Use the calculator as a baseline expectation, not a hard target. Wide individual variation within the IOM range is normal and healthy.
Sources and medical references
The ranges and weekly targets come from the IOM's 2009 guidance and corroborating sources.