Pregnancy Weight Gain Calculator — Free IOM-Based Tool

How to Use the Pregnancy Weight Gain Calculator

1. Select your unit system: Choose between Imperial (pounds, feet/inches) or Metric (kilograms, centimeters). The calculator adjusts all input fields and results to your chosen unit system. You can switch between systems at any time.
2. Enter your pre-pregnancy weight and height: Enter the weight you were before becoming pregnant and your height. These values are used to calculate your pre-pregnancy BMI, which determines which weight gain category applies to you. Use your weight from around the time of conception or your first prenatal visit.
3. Enter your current week of pregnancy: Enter which week of pregnancy you are currently in (1 to 42). The calculator prorates the total recommended gain to show how much you should have gained by this point. Results update instantly as you change the week.
4. Review your recommended weight gain: The results show your recommended cumulative weight gain range at your current week, your pre-pregnancy BMI and category, the total recommended gain for the full pregnancy, and the recommended weekly rate of gain. A progress bar shows how far along you are in your pregnancy.

These recommendations are based on IOM guidelines for singleton pregnancies. Twin and higher-order pregnancies have different targets. Your healthcare provider will set personalized weight gain goals based on your individual health circumstances, so use this calculator as a general reference rather than a strict target.

Weight Gain Calculation Formula

Variables Explained

• Pre-Pregnancy BMI: Calculated from your weight and height before pregnancy. This determines which IOM weight gain category applies: underweight (BMI below 18.5), normal weight (BMI 18.5-24.9), overweight (BMI 25.0-29.9), or obese (BMI 30.0+).
• Total Recommended Range: The IOM-recommended total weight gain for the entire 40-week pregnancy, based on BMI category. This range accounts for the baby, placenta, amniotic fluid, increased blood volume, breast tissue growth, uterine growth, and maternal fat stores.
• Current Week / 40: A progress fraction that prorates the total recommended gain to your current gestational week. At week 20, the fraction is 0.50, suggesting you should have gained about half the total recommended amount.
• Weekly Rate: The total recommended range divided by 40 weeks gives the average weekly gain rate. In practice, first trimester gain is slower, and second/third trimester gain is faster, but the linear approximation provides a useful baseline.

Step-by-Step Example

Calculate recommended weight gain for someone who is 5'4" (162.5 cm), 135 lbs (61.2 kg) pre-pregnancy, currently at week 24:

1. BMI: 61.2 / (1.625)² = 61.2 / 2.641 = 23.2
2. BMI Category: Normal Weight (18.5-24.9)
3. Total recommended: 25-35 lbs (11.5-16.0 kg)
4. Progress fraction: 24 / 40 = 0.60
5. Recommended at week 24: 11.5 x 0.60 to 16.0 x 0.60 = 6.9 - 9.6 kg (15.2 - 21.2 lbs)
6. Weekly rate: 11.5/40 to 16.0/40 = 0.29 - 0.40 kg/week (0.6 - 0.9 lbs/week)

Practical Examples

Example 1: Hannah at Normal Weight

Hannah, 31, is 5'6" (167.5 cm) and weighed 145 lbs (65.8 kg) before pregnancy. She is now at week 28 and has gained 18 pounds so far.

• Pre-pregnancy BMI: 65.8 / (1.675)² = 23.5 (Normal Weight)
• Total recommended: 25-35 lbs (11.5-16.0 kg)
• Recommended at week 28: 11.5 x 0.70 to 16.0 x 0.70 = 8.1-11.2 kg (17.8-24.7 lbs)
• Actual gain: 18 lbs (8.2 kg)
• Status: Within recommended range

Hannah's weight gain of 18 pounds at week 28 falls right within the recommended range. At her current rate of about 0.64 lbs per week, she is on track for a total gain of approximately 26 to 28 pounds by full term, which is well within the 25 to 35 pound target for her BMI category.

Example 2: Jessica at Higher BMI

Jessica, 34, is 5'3" (160 cm) and weighed 185 lbs (83.9 kg) before pregnancy. She is at week 20 and wants to know her target.

• Pre-pregnancy BMI: 83.9 / (1.60)² = 32.8 (Obese)
• Total recommended: 11-20 lbs (5.0-9.0 kg)
• Recommended at week 20: 5.0 x 0.50 to 9.0 x 0.50 = 2.5-4.5 kg (5.5-9.9 lbs)
• Weekly rate target: 0.3-0.5 lbs per week

Jessica's lower weight gain target reflects research showing that individuals with higher pre-pregnancy BMI already have adequate energy stores. Her healthcare provider emphasizes that this is not about restriction but about optimizing outcomes. Jessica focuses on nutrient-dense foods with adequate protein, fiber, and micronutrients rather than calorie counting. The BMI calculator provided her pre-pregnancy BMI baseline.

Example 3: Mia Who Is Underweight

Mia, 27, is 5'7" (170 cm) and weighed 115 lbs (52.2 kg) before pregnancy. She is at week 16 and concerned about gaining enough weight.

• Pre-pregnancy BMI: 52.2 / (1.70)² = 18.1 (Underweight)
• Total recommended: 28-40 lbs (12.5-18.0 kg)
• Recommended at week 16: 12.5 x 0.40 to 18.0 x 0.40 = 5.0-7.2 kg (11.0-15.9 lbs)
• Weekly rate target: 0.7-1.0 lbs per week

Mia's higher weight gain target reflects the need for her to build adequate energy reserves for the baby and for breastfeeding. Her provider recommends nutrient-dense, calorie-rich snacks between meals and tracks her weight gain closely. Mia adds about 300 extra calories per day in the second trimester and 450 in the third trimester. She and her nutritionist monitor both total gain and rate of gain to ensure healthy fetal growth.

IOM Weight Gain Recommendations

Tips and Complete Guide to Pregnancy Weight Management

Nutrition for Healthy Weight Gain

Focus on nutrient-dense foods rather than simply eating more. During the first trimester, no additional calories are typically needed. In the second trimester, add approximately 340 calories per day, and in the third trimester, add about 450 calories per day above your pre-pregnancy needs. These extra calories should come from protein (lean meats, beans, nuts, dairy), whole grains, fruits, vegetables, and healthy fats. Key nutrients during pregnancy include folic acid (600 mcg daily), iron (27 mg daily), calcium (1,000 mg daily), DHA omega-3 (200-300 mg daily), and vitamin D (600 IU daily). Our calorie calculator can help establish your baseline caloric needs.

Exercise During Pregnancy

Regular physical activity during pregnancy is safe and beneficial for most individuals. The American College of Obstetricians and Gynecologists recommends at least 150 minutes of moderate-intensity aerobic activity per week throughout pregnancy. Walking, swimming, stationary cycling, and prenatal yoga are excellent choices. Exercise helps manage healthy weight gain, reduces the risk of gestational diabetes, may shorten labor duration, improves mood and sleep, and aids postpartum recovery. Always get clearance from your healthcare provider before starting or continuing an exercise program during pregnancy.

Monitoring Weight Gain Patterns

Weight fluctuations of 1 to 2 pounds from day to day are normal during pregnancy due to fluid retention, meal timing, and bowel habits. Weigh yourself at the same time each week (ideally in the morning, after using the bathroom, in similar clothing) for consistent tracking. Plot your weight over time to identify trends rather than focusing on any single measurement. A sudden gain of more than 5 pounds in a week could indicate fluid retention and should be reported to your healthcare provider, as it may be a sign of preeclampsia.

Postpartum Weight Loss Expectations

Immediately after delivery, expect to lose about 10 to 15 pounds (the baby, placenta, and amniotic fluid). Over the next 6 weeks, additional fluid weight and blood volume normalize. Breastfeeding burns approximately 400 to 500 calories per day, which can support gradual weight loss. Most healthcare providers recommend waiting at least 6 weeks postpartum before beginning any structured weight loss program. A healthy rate of postpartum weight loss is 1 to 2 pounds per week. About 75% of individuals return to within 10 pounds of their pre-pregnancy weight within 12 months.

Common Mistakes to Avoid

• Eating for two in the literal sense: Pregnancy requires only 300 to 450 additional calories per day in the second and third trimesters — roughly an extra snack, not double portions.
• Restricting calories to limit weight gain: Undereating during pregnancy can deprive the baby of essential nutrients. Focus on quality over quantity rather than restricting intake.
• Weighing yourself daily and worrying about fluctuations: Daily weight varies by 1 to 2 pounds due to fluid and food. Track weekly trends instead of daily numbers.
• Comparing your weight gain to others: Recommended gain varies significantly based on pre-pregnancy BMI. Someone starting underweight needs to gain more than someone starting overweight.
• Ignoring rapid or sudden weight gain: A gain of more than 5 pounds in a single week may indicate fluid retention from preeclampsia — report this to your healthcare provider promptly.

Frequently Asked Questions