Pregnancy weight gain calculator

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

Sources and medical references

The ranges and weekly targets come from the IOM's 2009 guidance and corroborating sources.

• Institute of Medicine (National Academies) — Weight Gain During Pregnancy: Reexamining the Guidelines (2009)
• ACOG — Weight Gain During Pregnancy — Committee Opinion
• CDC — Weight Gain During Pregnancy
• Mayo Clinic — Pregnancy weight gain: What's healthy?