Pregnancy Weight Gain Calculator – Recommended Gain by BMI & Trimester

  • Adam
  • November 1, 2025

Free pregnancy weight gain calculator using Institute of Medicine guidelines. Calculate recommended weight gain by pre-pregnancy BMI for single and twin pregnancies. Track your progress weekly.

⚖️ 🤰 ⚖️

Pregnancy Weight Gain Calculator

Calculate your recommended pregnancy weight gain based on Institute of Medicine guidelines. Track your progress for a healthy pregnancy.

📋 Quick Navigation

⚖️ Calculate your recommended pregnancy weight gain! 🤰
kg/m² or use calculator method
1-40 weeks
in kg
in kg
in cm
in kg
in kg
1-40 weeks
Total Recommended Weight Gain
25-35 lbs
based on your pre-pregnancy BMI

BMI Category

Normal
pre-pregnancy

Weight Gained

5
lbs so far

Remaining

20-30
lbs to gain

Weekly Target

1
lbs/week

📊 Weight Gain Breakdown

Trimester Weeks Recommended Gain Average/Week Notes
First 1-12 1-4 lbs 0.1-0.3 lbs/week Minimal weight gain
Second 13-26 10-14 lbs ~1 lb/week Steady weight gain
Third 27-40 10-14 lbs ~1 lb/week Continued steady gain
TOTAL 1-40 25-35 lbs Overall pregnancy weight gain

📋 Institute of Medicine Guidelines

Weight Gain Recommendations by BMI

Pre-Pregnancy BMI Category Single Pregnancy Twin Pregnancy
<18.5 Underweight 28-40 lbs 37-54 lbs
18.5-24.9 Normal Weight 25-35 lbs 37-54 lbs
25.0-29.9 Overweight 15-25 lbs 31-50 lbs
≥30.0 Obese 11-20 lbs 25-42 lbs

First Trimester (Weeks 1-12)

Weight gain is minimal during the first trimester: 1-4 pounds total. This is because the baby is still very small. Most people don't "show" until around week 12-14. Nausea and morning sickness may actually prevent weight gain in the first trimester.

Second & Third Trimester (Weeks 13-40)

Weight gain accelerates in the second and third trimesters, averaging about 1 pound per week for women with normal pre-pregnancy BMI. This equals approximately 10-14 pounds per trimester. The rate may vary based on pre-pregnancy BMI category.

Why Weight Gain Matters

Adequate weight gain supports healthy fetal development, reduces risk of preterm birth, low birth weight, and gestational complications. Insufficient weight gain increases risks. Excess weight gain increases risk of gestational diabetes and preeclampsia. Working with your healthcare provider ensures appropriate gains for your specific situation.

💡 Note: These are guidelines, not absolute rules. Individual variation is normal and expected. Your healthcare provider should monitor your specific needs based on your health, pre-pregnancy weight, and pregnancy progression.

📊 Where Pregnancy Weight Goes

Weight Gain Breakdown

Component Weight Notes
Baby 7-8 lbs The fetus itself
Placenta 1-1.5 lbs Organ that nourishes baby
Amniotic Fluid 2 lbs Fluid surrounding baby
Enlarged Breast 1-3 lbs Preparation for breastfeeding
Enlarged Uterus 2 lbs Muscles stretch and expand
Extra Blood 4 lbs Volume increases 40-50%
Extra Water/Fluid 2-3 lbs In tissues and cells
Fat Stores 5-9 lbs Energy reserves for breastfeeding
TOTAL 25-35 lbs Average single pregnancy

What Doesn't Leave Immediately After Birth

Baby leaves: 7-8 lbs. Placenta & amniotic fluid leave: 3-4 lbs. Remaining after delivery: 15-20 lbs is typical immediately postpartum. Extra blood gradually decreases. Extra water is shed through sweating and urination. Fat stores are mobilized during breastfeeding.

Postpartum Weight Loss Timeline

Immediately after birth: 10-15 lbs lost. First 2 weeks: Additional 5-10 lbs through fluid loss. By 6 weeks: Many women back to pre-pregnancy weight if exclusively breastfeeding. 6-12 months: Remaining fat typically lost with breastfeeding and appropriate diet/exercise.

📌 Important: It takes 9 months to gain the weight, so allow 9+ months for it to come off postpartum. Breastfeeding accelerates weight loss through calorie expenditure. Patience and healthy habits are key for postpartum recovery.

🧮 Calculation Formulas

BMI Calculation

BMI = Weight (kg) / Height (m)²

Or with inches and pounds:
BMI = [Weight (lbs) / Height (inches)²] × 703

Example: 60 kg person, 165 cm tall
Height in meters = 165 / 100 = 1.65 m
BMI = 60 / (1.65)² = 60 / 2.72 = 22.1 kg/m²

Weight Gain Based on Week

For Weeks 1-12 (First Trimester):
Target Gain = 1-4 lbs total

For Weeks 13-40 (Second + Third Trimester):
Target Gain = (Week − 12) × 1 lb/week

Example: Week 20
Gain by week 20 = (20 − 12) × 1 = 8 lbs
Total expected = 4 + 8 = 12 lbs at week 20

Remaining Weight to Gain

Remaining = Maximum Gain − Current Gain

Example: Target 25-35 lbs, gained 12 lbs at week 20
Remaining = 25-35 − 12 = 13-23 lbs left to gain
Weeks left = 40 − 20 = 20 weeks
Rate = 13-23 / 20 = 0.65-1.15 lbs/week

Weekly Target Rate

For Normal BMI: ~1 lb/week in 2nd & 3rd trimester
Underweight: ~1.2 lbs/week
Overweight: ~0.6 lbs/week
Obese: ~0.5 lbs/week

For Twin Pregnancies: Add 0.5-1 lb/week to single rates

Caloric Needs During Pregnancy

Extra Calories Needed (after first trimester):
First Trimester: No extra calories needed
Second Trimester: +300 calories/day
Third Trimester: +300-500 calories/day

To gain 1 lb/week: Need 500 extra calories/day
(Since 3,500 calories = 1 pound, 3,500/7 = 500/day)

❓ Frequently Asked Questions

I'm overweight. Should I lose weight during pregnancy? +
No, pregnancy is not the time for weight loss. Even overweight and obese women should follow guidelines for weight gain (15-25 lbs for overweight, 11-20 lbs for obese). Weight loss during pregnancy can harm fetal development. Talk to your healthcare provider about safe exercise and nutrition during pregnancy and after delivery.
What if I'm not gaining enough weight? +
Inadequate weight gain can increase risk of preterm birth and low birth weight. If you're not gaining enough, discuss with your healthcare provider. You may need to eat more nutrient-dense foods, address morning sickness, or check for underlying issues. Eating an extra 300-500 calories daily helps reach targets.
What if I'm gaining too much weight? +
Excessive weight gain increases risk of gestational diabetes, preeclampsia, and difficult labor. If gaining too much, discuss with your healthcare provider. Don't diet, but focus on nutrient-dense foods, appropriate portions, and safe exercise. Your provider may refer you to a dietitian for personalized guidance.
Can I exercise to control weight gain? +
Yes! Regular exercise during pregnancy (as approved by your healthcare provider) helps manage weight gain and offers many benefits: improved energy, better sleep, reduced complications risk. Safe exercises include walking, swimming, prenatal yoga, and modified strength training. Always consult your provider before starting or continuing exercise programs.
Do I really need 300 extra calories per day? +
The 300-calorie recommendation is an average guideline. Individual needs vary based on activity level, metabolism, and whether it's single or multiple pregnancy. Some women need more, others less. Focus on healthy foods like proteins, whole grains, fruits, vegetables, and dairy rather than counting calories strictly. Your provider can advise your specific needs.
When do I lose the pregnancy weight? +
About 50% of weight is lost in the first month postpartum through fluid loss, baby, and placenta. The remaining 50% typically takes 6-12 months to lose through breastfeeding and healthy diet/exercise. Breastfeeding women often lose weight faster as milk production burns 300-500 calories daily.
Are these guidelines different for twins? +
Yes, twin pregnancies have higher weight gain recommendations: Underweight: 37-54 lbs. Normal weight: 37-54 lbs. Overweight: 31-50 lbs. Obese: 25-42 lbs. The higher gains account for two babies, two placentas, and increased maternal needs. Consult your healthcare provider for personalized guidance for your specific situation.

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