How to Track Pregnancy Weight Gain — Free IOM Calculator (2026)

Track recommended pregnancy weight gain based on your pre-pregnancy BMI with the brevio Pregnancy Weight Gain Calculator — free, no signup, runs entirely in your browser. Enter your pre-pregnancy weight, height, and current week to see the IOM-recommended range for your BMI category.

How much weight to gain during pregnancy depends on your pre-pregnancy body mass index (BMI). The Institute of Medicine (IOM) published updated guidelines in 2009 that remain the standard recommendation used by OBs and midwives worldwide.

How to Use the Tool

1. Select your unit system — metric (kg and cm) or imperial (lbs and ft/in).
2. Enter your pre-pregnancy weight and height. These are used to calculate your pre-pregnancy BMI.
3. Enter your current week of pregnancy (1–42).
4. Click Calculate to see your BMI category, total recommended gain range, and expected gain so far for your current week.

IOM Pregnancy Weight Gain Guidelines

The 2009 IOM recommendations by pre-pregnancy BMI:

• Underweight (BMI < 18.5): 28–40 lbs (12.5–18 kg) total
• Normal weight (BMI 18.5–24.9): 25–35 lbs (11.5–16 kg) total
• Overweight (BMI 25–29.9): 15–25 lbs (7–11.5 kg) total
• Obese (BMI ≥ 30): 11–20 lbs (5–9 kg) total

Weight gain is not linear throughout pregnancy. During the first trimester, gain is typically minimal (1–5 lbs total). Most weight gain occurs in the second and third trimesters at a rate of roughly 0.5–1 lb per week for normal-weight individuals.

Gaining within the recommended range is associated with better outcomes for both mother and baby, including lower risk of preterm birth, gestational diabetes, and cesarean delivery.

Frequently Asked Questions

What if I am carrying twins?

The IOM has separate guidelines for twin pregnancies: normal weight mothers carrying twins should gain 37–54 lbs; overweight mothers 31–50 lbs; obese mothers 25–42 lbs. This calculator covers singleton pregnancies only.

Does where the weight goes matter?

Yes. Not all pregnancy weight is fat — it includes the baby (7–8 lbs), placenta (1.5 lbs), amniotic fluid (2 lbs), uterus growth (2 lbs), breast tissue (2 lbs), blood volume increase (4 lbs), and fluid in maternal tissues (4 lbs). The fat reserve accounts for roughly 7 lbs in a typical 25–35 lb gain.

Should I try to restrict weight gain during pregnancy?

Restricting calories significantly during pregnancy is not recommended. If you are gaining more than the guidelines suggest, discuss dietary adjustments with your healthcare provider rather than self-restricting. Adequate nutrition is essential for fetal development.

Related tools: Pregnancy Due Date Calculator · BMI Calculator