Home › Health › Women's Health › Pregnancy Weight Gain

Pregnancy Weight Gain Calculator

IOM-based recommendations by pre-pregnancy BMI — track your week-by-week progress and compare singleton vs multiples.

Your Information

lbs
Week 1Week 42
Recommended Total Weight Gain
-- to -- lbs
Enter your information above
Pre-Pregnancy BMI
—
BMI Category
—
Current Week
—
Expected Gain by Now
—
Actual Gain
—
Difference
—
Wkly Rate (T2/T3)
—
Gain at Term
—
IOM 2009 Guidelines BMI = kg / m² Trimester-paced gain

IOM Weight Gain Curve

Chart: iom weight gain curve.

My Weight Log

Log your actual weight each week to track against your IOM target range. Your data stays in your browser.

0 entries logged

Actual vs Recommended

Chart: actual vs recommended.

Twin & Multiples Comparison

Compare IOM weight gain recommendations for singleton vs twin/triplet pregnancies based on your BMI category.

Singleton vs Multiples Gain Curves

Chart: singleton vs multiples gain curves.

Milestone Comparison

Week Trimester Singleton Range Multiples Range

Twin Pregnancy

  • Average delivery: ~37 weeks
  • Higher calorie needs (+600 kcal/day)
  • More frequent prenatal visits
  • Weight gain typically 37-54 lbs (normal BMI)

Triplet Pregnancy

  • Average delivery: ~34 weeks
  • Higher calorie needs (+900 kcal/day)
  • Specialist care recommended
  • Weight gain typically 50-65 lbs (normal BMI)
📋

How to Use This Calculator

1

Enter Pre-Pregnancy Info

Input your height, pre-pregnancy weight, and current gestational week.

2

View Your IOM Range

See the recommended total weight gain and weekly rate for your BMI category.

3

Track Week by Week

Log weigh-ins in the Tracker tab and compare your actual gain vs the recommended curve.

4

Compare Multiples

Switch to Twin/Multiples Mode to see adjusted guidelines for twin or triplet pregnancies.

❓

Frequently Asked Questions

Basics How much weight should I gain in the first trimester?
Most women gain only 1-5 pounds during the first trimester. Some women lose weight due to morning sickness, which is generally not a concern unless severe. The majority of pregnancy weight gain occurs in the second and third trimesters when the baby grows most rapidly.
Basics Is it safe to lose weight during pregnancy?
Intentional weight loss during pregnancy is generally not recommended. However, for women with a pre-pregnancy BMI over 30, modest weight gain (11-20 lbs) is the guideline, and some may gain less without concern. Focus on nutrient-dense foods rather than calorie restriction. Always discuss weight management with your healthcare provider.
Basics What happens if I gain too much weight during pregnancy?
Excessive weight gain increases the risk of gestational diabetes, preeclampsia, cesarean delivery, and having a larger baby (macrosomia). It can also make postpartum weight loss more difficult. If your gain exceeds the recommended range, talk to your provider about dietary adjustments and safe physical activity.
Basics Are the weight gain guidelines different for twins?
Yes. For twin pregnancies, the IOM recommends higher total weight gain: 37-54 lbs for normal BMI, 31-50 lbs for overweight, and 25-42 lbs for obese. Underweight women carrying twins should work with their provider for individualized targets. Use the Twin/Multiples tab to see the full comparison chart.
Basics Where does all the pregnancy weight go?
A typical 30 lb weight gain breaks down approximately as: baby (7-8 lbs), placenta (1.5 lbs), amniotic fluid (2 lbs), uterine growth (2 lbs), breast tissue (1-3 lbs), increased blood volume (3-4 lbs), body fluid retention (2-3 lbs), and maternal fat stores (6-8 lbs). Most of this weight is lost within weeks of delivery.
Advanced How is the weight log data stored?
All weight log data is stored locally in your browser using localStorage. It never leaves your device and is not sent to any server. You can export it as a CSV file or clear it at any time from the Week-by-Week Tracker tab.
⚡

Formula & Methodology

BMI Classification

BMI = Weight (kg) / Height (m)²

Pre-pregnancy BMI determines recommended weight gain range per IOM 2009 guidelines.

Weekly Gain Rate

2nd/3rd Trimester: 0.5–1.0 lbs/week depending on BMI

Most weight gain occurs in the second and third trimesters when the baby grows most rapidly.

Twin Adjustment

Twin total = Singleton total × 1.3–1.5

Twin pregnancies require significantly more weight gain, with delivery typically at ~37 weeks.

📖

Key Terms Explained

IOM Guidelines — Institute of Medicine recommendations for total pregnancy weight gain based on pre-pregnancy BMI category.
Gestational Weight Gain — Total weight gained during pregnancy, including baby, placenta, amniotic fluid, blood volume, and maternal fat stores.
Pre-Pregnancy BMI — Body Mass Index calculated from pre-pregnancy weight and height, used to determine weight gain recommendations.
Trimester — Pregnancy divided into three stages: T1 (weeks 1-13), T2 (weeks 14-27), and T3 (weeks 28-40).
Macrosomia — A newborn with excessive birth weight (over 8 lbs 13 oz), associated with excessive maternal weight gain.
👥

Real-World Examples

👩

Sarah, 29 — Normal BMI, Singleton (Week 20)

Tracking mid-pregnancy gain against her IOM target range

Pre-pregnancy Weight
135 lbs
Height
5’5”
Pre-pregnancy BMI
22.5 — Normal
Gestational Week
Week 20
IOM Target Range (Total)
25–35 lbs — On Track at +10 lbs
Current Weight
145 lbs (+10 lbs)
Expected at Week 20
~10 lbs
2nd/3rd Tri Rate
~1.0 lb/week
Projected Final Gain
~30 lbs

Sarah is exactly on pace. IOM recommends 1–4.4 lbs in the first trimester, then ~1.0 lb/week thereafter. At week 20, ~10 lbs is right at the midpoint. Continuing at 1.0 lb/week for 20 more weeks puts her at ~30 lbs total — well within the 25–35 lb target.

📄

Healthy Weight Gain During Pregnancy

Where the Weight Goes

A full-term pregnancy adds approximately: baby (7.5 lbs), placenta (1.5 lbs), amniotic fluid (2 lbs), uterus (2 lbs), breast tissue (2 lbs), blood volume (4 lbs), fluid retention (4 lbs), and maternal fat stores (5-9 lbs).

First Trimester Expectations

Most women gain only 1-5 lbs in the first trimester. Some lose weight due to nausea. This is normal. The bulk of healthy weight gain occurs in the second and third trimesters when the baby grows most rapidly.

Gaining Too Much or Too Little

Excessive gain increases risks of gestational diabetes, preeclampsia, and cesarean delivery. Insufficient gain is associated with preterm birth and low birth weight. If your gain is outside the recommended range, discuss nutrition strategies with your provider.

Multiple Pregnancies

Twin and triplet pregnancies require significantly more weight gain. The IOM recommends 37-54 lbs for normal-weight women carrying twins. Twins typically deliver at ~37 weeks, and triplets at ~34 weeks, so the gain curve is steeper and compressed into fewer weeks.

⚕ Pregnancy weight gain recommendations vary by individual. Consult your OB/GYN or registered dietitian for personalized guidance throughout your pregnancy.