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Pregnancy Weight Gain Calculator

Healthy weight gain during pregnancy supports your baby's development and your own well-being. The Institute of Medicine (IOM) provides evidence-based guidelines for total and weekly weight gain based on your pre-pregnancy Body Mass Index (BMI). This calculator estimates your recommended weight gain range for your current week of pregnancy.

Quick Answer

Recommended pregnancy weight gain is 25–35 lbs for normal-weight women (BMI 18.5–24.9) according to IOM guidelines.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter your pre-pregnancy weight, height, and current week above to calculate your recommended weight gain.

How the Formula Works

  1. Calculate your pre-pregnancy BMI from your height and weight.

    BMI = weight (kg) / height (m)^2

  2. Determine your BMI category: Underweight (< 18.5), Normal (18.5-24.9), Overweight (25.0-29.9), or Obese (>= 30.0).

    Category determines total gain range

  3. Look up the IOM recommended total weight gain range for your BMI category.

    e.g. Normal weight: 25-35 lbs total

  4. For the first trimester (weeks 1-13), the recommended total gain is 1-4.4 lbs.

    First trimester gain is relatively small

  5. For weeks 14-40, calculate current recommended gain using the weekly rate for your BMI category.

    Current gain = 1st trimester base + weekly rate x weeks past 13

How to Interpret Your Results

Weight gain recommendations are based on your pre-pregnancy BMI category. These ranges represent the total weight gain recommended across the entire pregnancy. Individual needs may vary, especially for those carrying multiples.

Underweight (BMI < 18.5)
28–40 — Recommended total gain: 28-40 lbs. About 1 lb/week in 2nd and 3rd trimesters.
Normal Weight (BMI 18.5-24.9)
25–35 — Recommended total gain: 25-35 lbs. About 1 lb/week in 2nd and 3rd trimesters.
Overweight (BMI 25.0-29.9)
15–25 — Recommended total gain: 15-25 lbs. About 0.6 lb/week in 2nd and 3rd trimesters.
Obese (BMI >= 30.0)
11–20 — Recommended total gain: 11-20 lbs. About 0.5 lb/week in 2nd and 3rd trimesters.

Limitations

  • These guidelines are for singleton pregnancies only. Women carrying twins or multiples have different recommended weight gain ranges.
  • IOM guidelines are population-level recommendations and may not account for individual medical conditions, nutritional needs, or complications.
  • The calculator uses pre-pregnancy BMI, which has known limitations and does not distinguish between muscle mass and fat.
  • Weight gain during pregnancy is not always linear. Some women gain more in certain trimesters than others, and this is often normal.
  • This tool is for informational purposes only and should not replace prenatal care or guidance from your healthcare provider.

Frequently Asked Questions

How much weight should I gain during pregnancy?
The recommended total weight gain depends on your pre-pregnancy BMI. For normal-weight women (BMI 18.5-24.9), the IOM recommends 25-35 lbs. Underweight women should gain 28-40 lbs, overweight women 15-25 lbs, and obese women 11-20 lbs.
When does most pregnancy weight gain occur?
Most weight gain occurs during the second and third trimesters. During the first trimester, only 1-4.4 lbs of gain is typical. After week 13, weight gain tends to be more steady at the recommended weekly rate for your BMI category.
Is it safe to lose weight during pregnancy?
Intentional weight loss during pregnancy is generally not recommended. If you are concerned about your weight, speak with your healthcare provider. They can help you develop a safe nutrition and activity plan tailored to your situation.
What if I am gaining more or less than recommended?
Minor variations from the recommended range are common and usually not a concern. However, significant deviations may warrant a conversation with your healthcare provider, who can assess whether any adjustments to diet or activity are needed.
Do IOM guidelines apply to twin pregnancies?
No. The IOM has separate guidelines for twin pregnancies with higher recommended weight gain ranges. This calculator is designed for singleton pregnancies only. Consult your provider for twin-specific guidance.

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