Free Pregnancy Weight Gain Calculator

See exactly what healthy weight gain looks like for your unique body and situation!

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  By: Tali Ditye, Ph.D., Co-founder

  Updated: October 23, 2025

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Whether you're just starting your pregnancy journey or tracking your progress week by week, our interactive calculator provides personalized weight gain curves with percentile ranges, helping you understand what's healthy for you and your baby.

Our Pregnancy Weight Gain Calculator

Our interactive calculator provides a personalized, week-by-week weight gain trajectory based on your pre-pregnancy BMI.

Simply enter your pre-pregnancy height and weight, how many babies you're expecting (single, twins, triplets), and click "Calculate my Trajectory."

Be sure to print or email the results to yourself!

Pregnancy Weight Gain: A Complete Week-by-Week Guide

Healthy weight gain during pregnancy is one of the most common concerns for expectant mothers.

While every pregnancy is unique, medical guidelines provide valuable benchmarks to help ensure both maternal and fetal health throughout the nine-month journey.

We explain how much weight you should gain during pregnancy, when you'll gain it, and what factors influence healthy weight gain patterns.

How Much Weight Should I Gain During Pregnancy?

The amount of weight you should gain during pregnancy depends primarily on your pre-pregnancy body mass index (BMI).

The Institute of Medicine (IOM) established evidence-based guidelines in 2009 that remain the gold standard for pregnancy weight gain recommendations used by obstetricians and midwives worldwide.

These are below:

Recommended Weight Gain by Pre-Pregnancy BMI

Singleton Pregnancy (One Baby)

Twin Pregnancy (Two Babies)

Triplet Pregnancy (Three Babies)

Special considerations: Specific guidelines vary significantly based on individual circumstances, and close monitoring by a maternal-fetal medicine specialist is essential. Always consult your healthcare provider for personalized recommendations, especially for higher-order multiple pregnancies.

Understanding Week-by-Week Weight Gain Patterns

Weight gain during pregnancy doesn't happen uniformly. The pattern follows a predictable curve that varies by trimester.

First Trimester (Weeks 1-13): The Slow Start

During the first trimester of pregnancy, weight gain is typically minimal, ranging from 1 to 5 pounds total for the entire 13-week period. Many women experience little to no weight gain, and some may even lose weight due to morning sickness and nausea.

This limited weight gain is completely normal and expected. The developing baby is still very small during this stage, weighing only about 1-2 ounces by the end of the first trimester. Most of the early pregnancy changes involve hormonal shifts and other internal adaptations rather than significant weight increases.

What to expect in the first trimester:

• Weeks 1-4: Minimal to no weight change
• Weeks 5-8: 0-2 pounds gained (or possibly weight loss from nausea)
• Weeks 9-13: 1-3 additional pounds
• Total first trimester gain: 1-5 pounds

Second Trimester (Weeks 14-27): Steady Growth

The second trimester of pregnancy marks the beginning of consistent, steady weight gain. This is when most women start to "show" and notice significant changes in their body. Morning sickness typically subsides, appetite returns, and the baby enters a rapid growth phase.

Weight gain during this period follows a more predictable weekly rate based on your BMI category. For women with a normal pre-pregnancy BMI, expect to gain approximately 1 pound per week, totaling about 12-14 pounds during the second trimester.

What to expect in the second trimester:

• Consistent weekly weight gain begins
• Baby bump becomes visible
• Increased appetite and energy levels
• Baby grows from 3 ounces to about 2 pounds

Third Trimester (Weeks 28-40): Final Push

The third trimester of pregnancy continues the steady weight gain pattern established in the second trimester. The baby gains most of their birth weight during these final weeks, and your body prepares for labor and breastfeeding by storing additional nutrients and increasing blood volume.

Weight gain typically continues at the same weekly rate until around week 37, when it may slow slightly or plateau as the body prepares for delivery. Some women notice they stop gaining weight or even lose a pound or two in the final week or two before labor begins.

What to expect in the third trimester:

• Continued steady weight gain through week 36-37
• Possible plateau or slight decrease in the final weeks
• Baby gains approximately 5 pounds during this trimester
• Increased swelling may affect weight measurements

Where Does the Weight Go?

Many expectant mothers wonder where all the pregnancy weight actually goes, especially since a full-term baby typically weighs only 7-8 pounds.

The answer reveals the remarkable complexity of pregnancy physiology:

Distribution of a 30-pound pregnancy weight gain:

• Baby: 7-8 pounds
• Placenta: 1-2 pounds
• Amniotic fluid: 2 pounds
• Uterus enlargement: 2 pounds
• Breast tissue: 1-2 pounds
• Blood volume increase: 3-4 pounds
• Fluid retention: 2-3 pounds
• Maternal fat stores: 6-8 pounds

The maternal fat stores serve an important purpose: providing energy reserves for breastfeeding after delivery.

Your body naturally prepares to nourish your baby, even after birth!

Why Healthy Weight Gain Matters

Gaining the appropriate amount of weight during pregnancy significantly impacts both maternal and fetal outcomes.

Both inadequate and excessive weight gain can pose risks.

Risks of Insufficient Weight Gain

Not gaining enough weight during pregnancy can lead to:

• Low birth weight baby (less than 5.5 pounds)
• Preterm delivery
• Developmental delays
• Difficulty breastfeeding due to inadequate milk supply
• Weakened maternal immune system

Risks of Excessive Weight Gain

Gaining too much weight during pregnancy increases the risk of:

• Gestational diabetes
• High blood pressure and preeclampsia
• Cesarean delivery
• Macrosomia (baby larger than 9 pounds)
• Postpartum weight retention
• Childhood obesity in the baby
• Difficulty losing weight after delivery

Factors That Influence Pregnancy Weight Gain

While the IOM guidelines provide excellent benchmarks, several factors can influence your individual weight gain pattern:

Age

Younger mothers (especially teenagers) may need to gain more weight to support both their own continued growth and the baby's development.

Older mothers may have different metabolic patterns that affect weight gain.

Pre-Pregnancy Nutritional Status

Women who were undernourished before pregnancy may need to gain more weight, while those who were well-nourished may gain at the lower end of the recommended range.

Activity Level

Regular exercise during pregnancy can help manage weight gain while providing numerous health benefits.

Women who maintain active lifestyles may gain weight differently than sedentary mothers.

Genetics

Family history and genetic factors play a role in how your body responds to pregnancy.

Some women naturally gain more fluid or retain weight differently based on their genetic makeup. When in doubt, ask your mom and aunt about their experiences!

Multiple Pregnancies

Carrying twins, triplets, or more requires significantly more weight gain to support multiple babies and placentas.

Twin pregnancies typically require 37-54 pounds of weight gain for normal BMI mothers.

Morning Sickness Severity

Severe nausea and vomiting (hyperemesis gravidarum) can prevent adequate weight gain in early pregnancy and may require medical intervention.

How Our Pregnancy Weight Gain Calculator Works

Our calculator uses the same medical framework employed by obstetricians and healthcare providers worldwide.

Here's what makes it unique and valuable:

Based on IOM 2009 Guidelines

The calculator implements the Institute of Medicine's 2009 Weight Gain During Pregnancy guidelines, which represent the most current evidence-based recommendations.

These guidelines were developed through comprehensive review of pregnancy outcomes research and are endorsed by the American College of Obstetricians and Gynecologists (ACOG).

Percentile Curves Like Growth Charts

Just as pediatricians use growth charts to track your baby's development after birth, our calculator provides percentile curves (10th, 25th, 50th, 75th, and 90th) to show the healthy range of weight gain throughout pregnancy.

The shaded "healthy zone" represents where most healthy pregnancies fall, giving you context for your individual journey.

Realistic Week-by-Week Modeling

Unlike simple calculators that just provide a total target number, our tool models the actual pattern of pregnancy weight gain:

• First trimester sigmoid curve: We use a mathematical sigmoid (S-curve) function to model the slow start of weight gain typical in early pregnancy, accounting for the minimal gain or possible loss from morning sickness.
• Linear second and third trimester progression: From week 14 onward, the calculator uses consistent weekly rates based on your BMI category, matching the steady growth pattern observed in healthy pregnancies.

Personalized to Your BMI and Number of Expected Babies

The calculator automatically determines your BMI category and adjusts all recommendations accordingly. A woman who starts pregnancy underweight has different nutritional needs than someone who begins at a higher weight, and the calculator reflects these differences in every calculation.

The calculator is also personalized to whether you're expecting a single baby, twins, or triplets.

Tips for Healthy Weight Gain During Pregnancy

Focus on Nutrition Quality, Not Quantity

Pregnancy is not the time to "eat for two" in terms of calories. During the first trimester, you need virtually no additional calories. In the second and third trimesters, you only need about 300-500 extra calories per day (the equivalent of a snack like yogurt with fruit and nuts).

Instead, focus on nutrient-dense foods:

• Lean proteins: Chicken, fish, beans, eggs, tofu
• Whole grains: Oatmeal, quinoa, whole wheat bread, brown rice
• Colorful fruits and vegetables: Aim for a rainbow of colors
• Healthy fats: Avocados, nuts, olive oil, fatty fish
• Calcium-rich foods: Dairy products, fortified plant milks, leafy greens
• Iron sources: Red meat, spinach, legumes, fortified cereals

Stay Active

Unless your healthcare provider advises otherwise, aim for 150 minutes of moderate exercise per week. Safe pregnancy exercises include:

• Walking
• Swimming
• Prenatal yoga
• Stationary cycling
• Low-impact aerobics
• Strength training with modifications

Exercise helps manage weight gain, reduces pregnancy discomforts, improves mood, and may lead to easier labor and delivery.

Monitor Your Weight Regularly

Weigh yourself weekly at the same time of day, preferably in the morning after using the bathroom and before eating.

Use the same scale for consistency. Track your weight in a journal or app to identify patterns.

Stay Hydrated

Drink at least 8-10 glasses of water daily. Adequate hydration supports increased blood volume, prevents constipation, reduces swelling, and helps distinguish between true hunger and thirst.

Listen to Your Body

Eat when you're hungry and stop when you're satisfied. Pregnancy hormones can affect hunger cues, but tuning into your body's signals helps maintain healthy eating patterns.

Manage Cravings Wisely

Cravings are normal, but they don't need to derail your nutrition.

If you're craving something unhealthy, try to satisfy it with a smaller portion or find a healthier alternative.

If you're craving ice cream, try Greek yogurt with fruit. If you're craving chips, try roasted chickpeas!

When to Talk to Your Doctor About Weight Gain

Schedule a conversation with your healthcare provider if you experience:

• Sudden weight gain: More than 3-5 pounds in a week, which could indicate preeclampsia or excessive fluid retention
• No weight gain: Failing to gain weight by the second trimester
• Excessive vomiting: Inability to keep food down, which may require medical intervention
• Rapid weight gain: Gaining significantly more than recommended in any trimester
• Weight loss: Losing weight in the second or third trimester
• Concerns about eating: Disordered eating thoughts or behaviors

What If I'm Not Gaining According to Guidelines?

First, remember that guidelines are ranges, not rigid rules. Some variation is completely normal and healthy.

However, if you're significantly outside the recommended range, here's what to consider:

Gaining Too Little

If you're not gaining enough weight:

• Eat more frequent, smaller meals throughout the day
• Add healthy calorie-dense foods like nuts, nut butters, avocados, and olive oil
• Drink smoothies or protein shakes between meals
• Reduce exercise intensity if you're very active
• Work with a registered dietitian for personalized meal planning
• Rule out medical conditions affecting appetite or absorption

Gaining Too Much

If you're gaining more than recommended:

• Review your portion sizes and eating frequency
• Reduce consumption of empty-calorie foods (sweets, fried foods, sugary drinks)
• Increase physical activity within safe limits
• Ensure you're drinking enough water, not liquid calories
• Keep a food diary to identify patterns
• Never restrict calories or diet during pregnancy without medical supervision

Important: Never try to lose weight during pregnancy. Even if you're gaining more than recommended, the goal is to slow the rate of gain, not to lose weight.

Postpartum Weight Loss

After delivery, you'll immediately lose approximately 12-14 pounds from the baby, placenta, and amniotic fluid. Over the following weeks, you'll lose additional weight from decreased blood volume and fluid loss.

Most women return to their pre-pregnancy weight within 6-12 months, though this timeline varies significantly. Breastfeeding burns approximately 300-500 calories per day and can help with postpartum weight loss, though it's not a guarantee.

Give yourself grace and patience. Your body accomplished the remarkable feat of growing and birthing a human. Weight loss should be gradual and healthy, focusing on nutritious eating and gentle exercise once cleared by your healthcare provider.

Special Considerations

Gestational Diabetes

If you develop gestational diabetes, your healthcare provider may adjust your weight gain goals and provide specific dietary guidelines. Managing blood sugar becomes the primary focus, which may naturally affect weight gain patterns.

Preeclampsia Risk

Sudden, rapid weight gain accompanied by swelling, headaches, or vision changes requires immediate medical attention as these can be signs of preeclampsia, a serious pregnancy complication.

Eating Disorders History

If you have a history of eating disorders, pregnancy weight gain can be emotionally challenging. Work closely with both your obstetric provider and a mental health professional experienced in perinatal care.

Multiple Pregnancies

Twin, triplet, and higher-order multiple pregnancies require significantly more weight gain. For twins, women with normal BMI should gain 37-54 pounds. Your healthcare provider will give you specific recommendations based on your situation.

The Bottom Line

Healthy pregnancy weight gain is essential for both you and your baby's well-being. While the IOM guidelines provide valuable benchmarks, remember that every pregnancy is unique. Only your healthcare provider knows your individual medical history, risk factors, and circumstances and can provide personalized guidance.

Use our pregnancy weight gain calculator as an educational tool only, to understand what healthy weight gain might look like for your body. Track your progress, maintain good nutrition and activity habits, and communicate openly with your healthcare team about any concerns.

Most importantly, approach pregnancy weight gain with self-compassion. Your body is performing an incredible task, and those extra pounds serve important purposes in supporting your growing baby and preparing for the demands of motherhood.

Frequently Asked Questions

Q: Can I diet during pregnancy if I'm overweight?

A: No, pregnancy is not the time to try to lose weight, even if you began pregnancy overweight. However, your healthcare provider may recommend gaining at the lower end of the range for your BMI category and focusing on nutrient-dense foods while limiting empty calories.

Q: Is it normal to gain most of my weight in the third trimester?

A: Weight gain should be fairly consistent in the second and third trimesters. If you're gaining most of your weight in the third trimester, discuss this pattern with your healthcare provider to ensure there are no underlying concerns.

Q: I lost weight in my first trimester due to morning sickness. Is this harmful?

A: Mild weight loss (up to 5 pounds) in the first trimester due to morning sickness is common and typically not harmful. However, severe or prolonged weight loss requires medical attention. Most women catch up on weight gain in the second trimester.

Q: How often should I weigh myself during pregnancy?

A: Weekly weighing at home is sufficient for most women. Weigh yourself at the same time of day, preferably in the morning, for the most consistent tracking. Your healthcare provider will also weigh you at each prenatal appointment.

Q: Do I need to gain more weight if I'm having a boy versus a girl?

A: No, the baby's sex doesn't significantly affect weight gain recommendations. The same guidelines apply regardless of whether you're carrying a boy or girl.

Q: What if I'm pregnant with twins?

A: Twin pregnancies require more weight gain. Women with normal pre-pregnancy BMI carrying twins should gain 37-54 pounds. Your healthcare provider will give you specific recommendations based on your BMI and the number of babies.

Q: Can I use this calculator if I'm using IVF or had fertility treatments?

A: Yes, the weight gain guidelines are the same regardless of how you conceived. The calculator works for all singleton pregnancies based on your pre-pregnancy BMI.

Q: My weight gain is below the 10th percentile. Should I be worried?

A: Not necessarily. The percentiles represent a range of healthy outcomes. If you're slightly below the 10th percentile but your baby is growing well and you feel healthy, this may be normal for you. However, discuss any concerns with your healthcare provider.

Medical References

This article and calculator are based on the following authoritative medical sources:

1. Institute of Medicine (US) and National Research Council (US) Committee to Reexamine IOM Pregnancy Weight Guidelines. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington (DC): National Academies Press (US); 2009.
2. American College of Obstetricians and Gynecologists. "Weight Gain During Pregnancy." Committee Opinion No. 548. Obstet Gynecol. 2013;121:210-2.
3. Centers for Disease Control and Prevention. "Weight Gain During Pregnancy." 
4. Diouf, I., et al. (2012). Specific role of maternal weight change in the first trimester of pregnancy on birth size. Maternal & Child Nutrition.
5. Herring, S. J., et al. (2011). Optimizing weight gain in pregnancy to prevent obesity in women and children. Diabetes, Obestity, and Metabolism.
6. Hutcheon, J. A., et al. (2018). Good practices for observational studies of maternal weight and weight gain in pregnancy. Paediatric and Perinatal Epidemiology.