Calculators Fit
● Pregnancy & wellness

Gestational Weight Gain recommended by week.

Find out how much weight is recommended during pregnancy based on your pre-pregnancy BMI — using the IOM 2009 guidelines — and track where you stand today.

🤰
Gestational Weight Gain
IOM 2009 recommendations by pre-pregnancy BMI category
✏️

Your data

lb
in
wk
lb
📊

Your result

—
Pre-pregnancy BMI
Total recommended gainIOM 2009 range—
Expected gain at week —mid-range estimate—
Enter your data above
Advertisement
Display · data-ad-format="auto"

How it's calculated

IOM 2009 guidelines: weight gain by BMI category

The Gestational Weight Gain calculator uses the Institute of Medicine (IOM) 2009 recommendations. Your pre-pregnancy BMI determines the target range: underweight (<18.5) should gain 12.5–18 kg; normal weight (18.5–24.9) should gain 11.5–16 kg; overweight (25–29.9) should gain 7–11.5 kg; and obese (≥30) should gain 5–9 kg for a singleton pregnancy.

First, your pre-pregnancy BMI is computed from weight and height. The BMI category then determines the recommended total weight gain range for the full 40 weeks. To estimate expected gain at your current gestational week, the calculator applies the IOM model: approximately 0.5–2 kg in the first trimester (weeks 1–12), then a steady weekly rate based on the midpoint of the recommendation from week 13 onward.

BMI = weight (kg) ÷ height (m)²
Expected gain (wk ≥13) = T1 gain + weekly rate × (week − 12)
Weekly rate = (total midpoint − T1 gain) ÷ 28
  1. 1
    Convert inputs and compute pre-pregnancy BMI
    —
  2. 2
    Look up IOM 2009 recommended range for your BMI category
    —
  3. 3
    Estimate expected weight gain at your gestational week
    —
  4. 4
    Compare your current gain to the expected range (if provided)
    —

Understand the terms

IOM Guidelines (2009)
Recommendations from the Institute of Medicine (now National Academy of Medicine) specifying gestational weight gain ranges for singleton pregnancies by pre-pregnancy BMI category.
Pre-pregnancy BMI
Body Mass Index calculated from your weight and height before conception. It classifies nutritional status (underweight, normal, overweight, obese) and drives the recommended gain range.
Gestational weight gain
Total weight gained from conception to delivery. It includes the baby, placenta, amniotic fluid, uterine enlargement, breast tissue, blood volume, and maternal fat stores.
Macrosomia
A condition where a baby is larger than average (birth weight >4 kg / 8 lb 13 oz), often linked to excessive gestational weight gain and gestational diabetes. Associated with higher risk of birth complications.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes, based on IOM 2009 guidelines for singleton pregnancies. Actual recommendations depend on your individual case, multiple gestation status, and healthcare provider's assessment. This tool does not substitute prenatal medical care or advice from your OB-GYN or midwife.
Advertisement
In-article · data-ad-layout="in-article"

Frequently asked questions — Gestational Weight Gain

How much weight should I gain during pregnancy?
According to the IOM 2009 guidelines, the recommended range depends on your pre-pregnancy BMI: underweight (<18.5) should gain 12.5–18 kg (28–40 lb); normal weight (18.5–24.9) should gain 11.5–16 kg (25–35 lb); overweight (25–29.9) should gain 7–11.5 kg (15–25 lb); and obese (≥30) should gain 5–9 kg (11–20 lb).
What is pre-pregnancy BMI and why does it matter?
Pre-pregnancy BMI is your body mass index calculated before becoming pregnant. It determines which IOM weight-gain category applies to you, since optimal gestational weight gain varies significantly based on your starting nutritional status. Starting underweight requires a larger gain; starting obese requires a more modest gain.
How is expected weekly weight gain distributed during pregnancy?
For most women with a normal BMI, minimal weight gain (about 1–2 kg) occurs in the first trimester. From weeks 13–40, a steady gain of about 0.35–0.5 kg per week is typical. This calculator estimates the expected gain at any week using the IOM midpoint rate after week 12.
What happens if I gain too much or too little weight during pregnancy?
Excessive gestational weight gain is linked to macrosomia (large-for-gestational-age babies), caesarean delivery, gestational diabetes, and postpartum weight retention. Insufficient gain is associated with preterm birth, low birth weight, and nutrient deficiencies. Always discuss your individual target with your OB-GYN or midwife.
Does the calculator work for twin pregnancies?
No. This calculator follows the IOM 2009 guidelines for singleton pregnancies only. Twin and multiple pregnancies have different weight-gain recommendations and higher total targets. For multiple gestations, consult your healthcare provider or midwife for individualised guidance.

📚 Learn more — official sources

📋 Guideline IOM 2009 — Weight Gain During Pregnancy: Reexamining the Guidelines The foundational report by the Institute of Medicine setting gestational weight gain ranges by pre-pregnancy BMI for singleton pregnancies, still the primary clinical reference. See official source → 🏛️ Organization ACOG Committee Opinion — Weight Gain During Pregnancy American College of Obstetricians and Gynecologists clinical guidance endorsing IOM recommendations and providing practical advice for clinicians and patients. See official source → 🏛️ Organization CDC — Gestational Weight Gain Centers for Disease Control and Prevention overview of recommended pregnancy weight gain, health implications, and surveillance data on US pregnancy outcomes. See official source → 🏛️ Organization WHO — Maternal health and nutrition World Health Organization guidance on maternal nutrition, healthy pregnancy, and evidence-based antenatal care recommendations for improving pregnancy outcomes globally. See official source →

About the Gestational Weight Gain Calculator

This calculator applies the Institute of Medicine (IOM) 2009 guidelines — the primary clinical reference for recommended weight gain during singleton pregnancies. The guidelines set ranges by pre-pregnancy BMI to optimize outcomes for both mother and baby, balancing the risks of gaining too little (preterm birth, low birth weight) against gaining too much (macrosomia, gestational diabetes, caesarean delivery).

The weight gain curve chart gives a visual reference of where your gain sits relative to the expected range at your current gestational week. Note that individual circumstances — including multiple gestations, maternal age, pre-existing conditions and clinical history — may justify different targets. Always consult your healthcare provider for personalized advice.

Advertisement
Multiplex · data-ad-format="autorelaxed"