Pregnancy Weight Gain Calculator — IOM Ranges by Week
Find your recommended total pregnancy weight gain from your pre-pregnancy BMI using the Institute of Medicine guidelines endorsed by ACOG, see the typical weekly rate, and check how your gain so far compares.
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Target Gain by Week
Cumulative gain range: first-trimester gain, then a steady path to the IOM total range at 40 weeks.
| Week | Gain So Far | Weight Range |
|---|
How this calculator works
Pre-pregnancy BMI = weight (kg) ÷ height (m)². The Institute of Medicine (IOM) 2009 guidelines, endorsed by ACOG, then set the total gain:
| Pre-pregnancy BMI | One baby | Weekly (2nd–3rd tri.) | Twins (provisional) |
|---|---|---|---|
| Underweight (<18.5) | 28–40 lb (12.5–18 kg) | 1–1.3 lb (0.44–0.58 kg) | No recommendation |
| Normal (18.5–24.9) | 25–35 lb (11.5–16 kg) | 0.8–1 lb (0.35–0.50 kg) | 37–54 lb (17–25 kg) |
| Overweight (25–29.9) | 15–25 lb (7–11.5 kg) | 0.5–0.7 lb (0.23–0.33 kg) | 31–50 lb (14–23 kg) |
| Obese (≥30) | 11–20 lb (5–9 kg) | 0.4–0.6 lb (0.17–0.27 kg) | 25–42 lb (11–19 kg) |
The week-by-week path assumes about 1.1–4.4 lb (0.5–2 kg) in the first trimester, as the IOM report does, then a steady rise to the total range at 40 weeks.
By Suhaib Hassan · Reviewed 28 September 2026 against the IOM 2009 report and ACOG Committee Opinion 548 · How CalculatePilot verifies formulas →
A worked example
At 5′5″ (1.651 m) and 140 lb (63.5 kg) before pregnancy, BMI = 63.5 ÷ 1.651² = 23.3 — normal weight — so the recommended total gain is 25–35 lb, a final weight of about 165–175 lb. At 20 weeks, the path suggests a gain of roughly 7–12 lb so far.
Why it matters
Gaining within the recommended range is linked with fewer complications for mother and baby. Gaining too much raises the chance of gestational diabetes, a large baby and keeping weight on after birth; too little is linked with preterm birth and low birth weight. The IOM did not set a twin range for underweight women because of limited evidence. This is information, not medical advice — your care team may set a different target for you.
Sources
- Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press, 2009.
- ACOG Committee Opinion No. 548 — Weight Gain During Pregnancy (2013, reaffirmed)
Common mistakes when tracking pregnancy weight gain
- Using today's weight to find your range. The IOM ranges depend on your pre-pregnancy BMI, not your BMI now.
- Applying the single-baby range to twins. Twin pregnancies have separate, higher provisional ranges.
- Chasing a weekly number. Gain is uneven from week to week. Look at the trend across several weeks, not one weigh-in.
- Weighing under different conditions. Time of day, clothing and the scale itself move the number by a pound or more. Use the same scale at the same time.
- Dieting to stay under the range. The ranges are targets for a healthy pregnancy, not a limit to push below.
When to talk to your care team
Call your midwife or doctor if you are gaining well outside the range for several weeks, if you are losing weight, or if you notice sudden weight gain together with swelling in the face or hands, a severe headache or changes in vision. Those can be signs of high blood pressure conditions such as preeclampsia and need prompt medical advice.
Read the guide: How much weight should you gain during pregnancy, week by week?
Frequently asked questions
How much weight should I gain in the first trimester?
The IOM report assumes a small first-trimester gain of about 1.1–4.4 lb (0.5–2 kg). Most of the gain comes in the second and third trimesters.
Why are twin ranges higher?
Carrying two babies needs more weight gain to support their growth. The IOM twin ranges are provisional, and no range was set for underweight women because the evidence was too limited.
What if I'm gaining more or less than the range?
Weight gain varies week to week. If you're consistently above or below the range, talk to your care team — they can look at your diet, activity and health and suggest changes safely.
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