Health July 13, 2026 · 8 Min Read

Pregnancy Weight Gain by Week – Guide & Formulas

Track and plan healthy maternal weight gain throughout pregnancy based on your pre-pregnancy BMI and current gestational week.

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Put these formulas into practice with our instant, step-by-step Pregnancy Weight Gain by Week.

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Track and plan healthy **pregnancy weight gain** throughout all three trimesters using our comprehensive **gestational weight gain calculator**. Maternal weight gain is a natural and necessary part of pregnancy, supporting the growing fetus, placenta, amniotic fluid, and increased maternal blood volume. This **pregnancy weight gain by week** calculator provides healthy, personalized weekly weight gain trajectories based on guidelines from the **Institute of Medicine (IOM)** and **American College of Obstetricians and Gynecologists (ACOG)**. Whether you need to track weight gain during the **first trimester**, **second trimester**, or **third trimester**, our calculator helps you understand how much weight to gain based on your pre-pregnancy BMI category and whether you are carrying a single baby or twins.

Key Takeaway

Use the free Pregnancy Weight Gain by Week to track and plan healthy maternal weight gain throughout pregnancy based on your pre-pregnancy bmi and current gestational week. Get instant results with step-by-step explanations.

How to Use the Pregnancy Weight Gain by Week

  1. Enter your pre-pregnancy height and weight to calculate your baseline BMI category.
  2. Enter your current week of pregnancy (1 to 40 weeks) to see your recommended weight gain range.
  3. Choose whether you are expecting a single baby or twins for personalized recommendations.
  4. Review your recommended cumulative weight gain range for your current gestational week.
  5. Compare your actual weight gain against the recommended range to identify any concerns.

The Formula

Recommended Gain (Weeks 13-40) = 1.1 to 4.4 lbs (Trimester 1) + (Current Week - 12) * Weekly Rate (based on BMI category)

Variable Definitions

  • First Trimester Gain: Standard initial adjustment gain during weeks 1-12 (typically 1.1 to 4.4 pounds total)
  • Weekly Rate: Optimal weight gain rate per week in the 2nd and 3rd trimesters (0.5 to 1.3 lbs/week depending on pre-pregnancy BMI)
  • BMI Category: Body Mass Index classification: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese (30+)
  • Total Recommended Gain: The total cumulative weight gain recommended for an entire pregnancy based on BMI category

Maternal Weight Gain Target

A woman with a normal pre-pregnancy BMI (21.5) is currently in gestational week 24.

  1. Step 1: Normal pre-pregnancy BMI target range is 25 to 35 lbs total gain for the entire pregnancy.
  2. Step 2: Allocate 3 lbs for the first trimester (Weeks 1-12) as recommended by IOM guidelines.
  3. Step 3: Calculate weeks in the 2nd trimester: 24 - 12 = 12 weeks of 2nd/3rd trimester.
  4. Step 4: Multiply by the normal BMI weekly rate: 12 weeks × 1.0 lb/week = 12 lbs.
  5. Step 5: Target weight gain by week 24 is 3 + 12 = 15 lbs (acceptable range: 13.5 to 17.5 lbs).

Financial Advisory Notice

This calculator provides general guidance based on IOM/ACOG guidelines and is not a substitute for personalized medical advice. Always consult your obstetrician or healthcare provider for pregnancy weight management. Individual recommendations may vary based on medical history, pregnancy complications, and specific health conditions.

Frequently Asked Questions