Your guide to healthy weight gain during pregnancy based on your unique needs.
Pregnancy Weight Gain Calculator
Enter your weight before you became pregnant.
Feet
Inches
First Trimester (Weeks 1-13)
Second Trimester (Weeks 14-27)
Third Trimester (Weeks 28-40)
Select your current stage of pregnancy.
Your Recommended Pregnancy Weight Gain
—
Pre-Pregnancy BMI:—
Recommended Total Gain (lbs):—
Recommended Gain This Trimester (lbs):—
Weight gain recommendations are based on pre-pregnancy BMI categories defined by the Institute of Medicine (IOM).
BMI is calculated using your height and weight. Total recommended gain varies by BMI, and rate of gain increases in the second and third trimesters.
Recommended RangeYour Target Gain
Weight Gain Progress Over Pregnancy
BMI Category
Pre-Pregnancy BMI Range
Recommended Total Weight Gain (lbs)
Recommended Rate (2nd/3rd Trimester)
Underweight
< 18.5
28-40
~1 lb/week
Normal Weight
18.5 – 24.9
25-35
~1 lb/week
Overweight
25.0 – 29.9
15-25
~0.5 lb/week
Obese
≥ 30.0
11-20
~0.5 lb/week
Recommended Pregnancy Weight Gain Guidelines by BMI
What is the American Pregnancy Weight Gain Calculator?
The American Pregnancy Weight Gain Calculator is a tool designed to help expectant mothers in the United States understand the recommended amount of weight they should gain throughout their pregnancy. This recommendation is not arbitrary; it is based on established guidelines from health organizations like the Institute of Medicine (IOM) and the American College of Obstetricians and Gynecologists (ACOG). These guidelines consider your Body Mass Index (BMI) before pregnancy, as this is a key indicator of your body's composition and metabolic state.
This calculator is essential for women who are pregnant or planning to become pregnant. It takes into account your individual starting point – your pre-pregnancy weight and height – to calculate your BMI. Based on your BMI category (underweight, normal weight, overweight, or obese), it then provides a target range for total weight gain during pregnancy and suggests a healthy rate of gain, particularly during the second and third trimesters when the baby grows most rapidly.
A common misconception is that pregnant women should "eat for two" and gain as much weight as possible. However, current medical advice emphasizes healthy, intentional weight gain. Gaining too little or too much weight can pose risks to both the mother and the baby. Another misconception is that the weight gain recommendation is uniform for all pregnancies; in reality, it's highly individualized based on pre-pregnancy BMI, which this calculator helps to determine.
Pregnancy Weight Gain Formula and Mathematical Explanation
The core of the American Pregnancy Weight Gain Calculator involves two main calculations: determining the pre-pregnancy Body Mass Index (BMI) and then using that BMI to establish recommended weight gain ranges.
1. Calculating Pre-Pregnancy BMI
BMI is a measure of body fat based on height and weight. For adults, the formula is:
BMI = (Weight in pounds / (Height in inches)²) * 703
Where:
Weight in pounds: Your weight before pregnancy in pounds.
Height in inches: Your height converted entirely into inches.
703: A conversion factor to adjust for the imperial system (pounds and inches).
To get height in inches:
Total Inches = (Feet * 12) + Inches
2. Determining Recommended Weight Gain
Once the pre-pregnancy BMI is calculated, it falls into one of four categories, each with specific weight gain recommendations set by the IOM:
Underweight: BMI less than 18.5. Recommended total gain: 28-40 lbs.
Normal Weight: BMI between 18.5 and 24.9. Recommended total gain: 25-35 lbs.
Overweight: BMI between 25.0 and 29.9. Recommended total gain: 15-25 lbs.
Obese: BMI of 30.0 or greater. Recommended total gain: 11-20 lbs.
The calculator also estimates the recommended gain for the current trimester. While the first trimester usually involves a gain of 1-4 lbs, the second and third trimesters see a more significant and steady increase. The approximate rate for the second and third trimesters is:
Normal weight & Underweight: ~1 lb per week.
Overweight & Obese: ~0.5 lb per week.
Variables Table:
Variable
Meaning
Unit
Typical Range
Pre-Pregnancy Weight
Maternal weight before conception
lbs
100 – 300+
Height
Maternal height
Feet & Inches
4'8″ – 6'2″+
Total Inches
Height converted to inches
Inches
56 – 74+
BMI
Body Mass Index
kg/m² (calculated)
< 18.5 (Underweight) to 30+ (Obese)
Trimester
Stage of pregnancy
Ordinal (1, 2, 3)
1, 2, 3
Recommended Total Gain
Target overall weight gain for pregnancy
lbs
11 – 40
Recommended Trimester Gain
Target gain for the current period
lbs
Calculated based on trimester and BMI
Variables Used in Pregnancy Weight Gain Calculation
Practical Examples (Real-World Use Cases)
Understanding how the calculator works is best illustrated with examples:
Recommended Gain This Trimester: ~13 lbs (assuming start of 2nd trimester, ~13 weeks * 1 lb/week)
Interpretation: Sarah falls into the normal BMI range. She should aim for a total weight gain of 25 to 35 pounds throughout her pregnancy. In her second trimester, gaining about one pound per week is generally recommended.
Recommended Gain This Trimester: ~6.5 lbs (assuming start of 3rd trimester, ~13 weeks * 0.5 lb/week)
Interpretation: Maria's BMI places her in the overweight category. Her target is to gain 15 to 25 pounds in total. During her third trimester, a gain of about half a pound per week is suggested.
How to Use This American Pregnancy Weight Gain Calculator
Using the American Pregnancy Weight Gain Calculator is straightforward and takes just a few moments.
Enter Pre-Pregnancy Weight: Input your weight in pounds from before you conceived.
Enter Height: Provide your height in feet and inches. The calculator will convert this to inches for the BMI calculation.
Select Current Trimester: Choose the trimester you are currently in (First, Second, or Third). This helps tailor the gain rate estimate.
Click 'Calculate': The tool will process your inputs and display the results.
How to Read Results:
Pre-Pregnancy BMI: This number indicates your weight status before pregnancy and categorizes you (Underweight, Normal, Overweight, Obese).
Recommended Total Gain: This is the target range of pounds you should aim to gain over the entire pregnancy.
Recommended Gain This Trimester: This provides a guideline for how much weight gain is appropriate for your current stage of pregnancy, based on the recommended weekly gain rate.
Decision-Making Guidance:
The results from this calculator are a guideline, not a strict rule. Always discuss your weight gain with your healthcare provider. They can offer personalized advice based on your specific health conditions, the baby's growth, and any other factors relevant to your pregnancy. This calculator empowers you with information to have more informed conversations with your doctor and to make conscious choices about nutrition and activity.
Key Factors That Affect Pregnancy Weight Gain Results
While the calculator provides a standard recommendation based on BMI, several other factors can influence individual pregnancy weight gain:
Maternal Age: Younger mothers might have different metabolic rates or nutritional needs compared to older mothers, potentially affecting ideal weight gain.
Multiple Gestation: Carrying twins, triplets, or more significantly increases the recommended weight gain. The calculator is designed for singleton pregnancies.
Previous Pregnancy History: If you gained significantly more or less than recommended in a previous pregnancy, your body might respond differently this time.
Underlying Health Conditions: Conditions like gestational diabetes, pre-existing diabetes, thyroid issues, or kidney disease can necessitate specific weight gain targets set by your medical team.
Nutritional Intake Quality: It's not just about the quantity of calories but the quality. A diet rich in nutrients supports healthy fetal development and appropriate maternal weight gain, whereas a diet high in empty calories can lead to excessive, unhealthy weight gain.
Physical Activity Levels: Regular, appropriate exercise during pregnancy helps manage weight gain, improves cardiovascular health, and can contribute to a healthier outcome for both mother and baby.
Socioeconomic Factors: Access to healthy foods, safe environments for exercise, and reliable healthcare can significantly impact a woman's ability to achieve recommended weight gain.
Rate of Weight Gain: Rapid weight gain, especially in the first trimester, can sometimes be a sign of fluid retention or excessive calorie intake, while slow gain might indicate insufficient nutrition. The focus should be on consistent, appropriate gain throughout the pregnancy.
Frequently Asked Questions (FAQ)
What if my pre-pregnancy weight was very low?
If your BMI was less than 18.5 (underweight), the recommendation is for a higher total weight gain (28-40 lbs). This ensures adequate nutrition for both you and your developing baby, supporting healthy growth and reducing risks associated with low birth weight.
Do I need to gain weight in the first trimester?
Weight gain in the first trimester is typically minimal, often between 1-4 pounds. Some women may even lose weight due to nausea and vomiting (morning sickness). The primary focus for growth is during the second and third trimesters.
Is gaining weight too fast a problem?
Yes, gaining weight too rapidly can increase risks such as excessive fetal growth (macrosomia), gestational diabetes, high blood pressure (preeclampsia), and difficulties with labor and delivery. It can also make postpartum weight loss more challenging.
What if I'm struggling to gain enough weight?
Consult your healthcare provider. They might recommend increasing your intake of nutrient-dense foods, adding healthy snacks between meals, or addressing underlying medical issues that could be hindering weight gain.
Does ethnicity affect weight gain recommendations?
While the BMI categories are generally standardized, some research suggests that certain health risks associated with specific BMI ranges might appear at different BMI levels for different ethnic groups. However, the core IOM recommendations based on BMI are the standard in the US. Always discuss individual concerns with your doctor.
How much of the weight gain is the baby?
The baby itself typically accounts for about 7-8 pounds of the total weight gain. The rest is made up of the placenta, amniotic fluid, increased blood volume, larger breasts, uterine growth, and maternal fat stores.
What are the risks of gaining too little weight?
Gaining too little weight can lead to a low birth weight baby, preterm birth, and developmental issues for the infant. It may also indicate insufficient calorie or nutrient intake for the mother's increased needs during pregnancy.
Should I track my weight gain daily?
While daily tracking isn't usually necessary, regular monitoring (e.g., weekly) can be helpful to ensure you are staying within your recommended range. Focus on trends over time rather than daily fluctuations. Discuss a tracking schedule with your healthcare provider.