Fetal Weight Estimator
Estimate fetal weight using the Hadlock formula or gestational age percentile lookup. Track your baby's growth throughout pregnancy.
Pregnancy Weight Gain Range Calculator
Find your recommended total and weekly pregnancy weight gain based on pre-pregnancy BMI. Uses IOM guidelines for all BMI categories.
in
lbs
Pre-Pregnancy BMI⧉
22.3
Normal Weight
Recommended Total Gain⧉
25–35 lbs
11.3–15.9 kg
Weekly Rate (2nd & 3rd Trimester)⧉
0.8–1 lbs/wk
0.36–0.45 kg/wk
BMI Category: Normal Weight
BMI 22.3 falls in the normal weight category. Recommended total weight gain is 25–35 lbs.
Trimester-by-Trimester Gains
| Trimester | Min Gain (lbs) | Max Gain (lbs) | Weeks |
|---|---|---|---|
| Trimester 1 | 10.4 | 13 | ~13 weeks |
| Trimester 2 | 20.8 | 26 | ~13 weeks |
| Trimester 3 | 31.2 | 39 | ~13 weeks |
BMI Categories & Recommendations
| BMI Category | BMI Range | Total Gain (lbs) | Weekly Rate (T2/T3) |
|---|---|---|---|
| Underweight | < 18.5 | 28–40 | 1.0–1.3 |
| Normal Weight | 18.5–24.9 | 25–35 | 0.8–1.0 |
| Overweight | 25–29.9 | 15–25 | 0.5–0.7 |
| Obese | ≥ 30 | 11–20 | 0.4–0.6 |
Weight Gain Visualization
Trimester 110.4–13 lbs
Trimester 220.8–26 lbs
Trimester 331.2–39 lbs
Planning notes, formulas, and examples
About the Pregnancy Weight Gain Range Calculator
This calculator uses your pre-pregnancy height and weight to estimate BMI and then show the recommended total pregnancy weight-gain range and the usual weekly pace used for the second and third trimesters.
The goal is not to create a rigid weekly scoreboard. It is to give you a reasonable range to discuss with your provider so you can interpret weigh-ins in context instead of guessing whether you are far above, below, or roughly on track.
That is especially helpful early in pregnancy, when many people want a simple reference point before symptoms, appetite, nausea, and activity changes start moving weight up or down.
When This Page Helps
Weight-gain guidance is tied to starting BMI, so one general rule does not fit every pregnancy. A range-based estimate helps you set expectations early, make sense of later weigh-ins, and have a more specific conversation with your provider about nutrition, nausea, swelling, twins, or other factors that can change the picture.
How to Use the Inputs
- Enter your height in inches.
- Enter your pre-pregnancy weight in pounds.
- View your BMI category and recommended weight gain ranges.
- Note the weekly target for the second and third trimesters.
- Share these targets with your healthcare provider.
Formula used
BMI = (weight_lbs / height_in² ) × 703
IOM Recommendations by BMI:
Underweight (< 18.5): 28-40 lbs total, 1.0-1.3 lbs/week
Normal (18.5-24.9): 25-35 lbs total, 0.8-1.0 lbs/week
Overweight (25-29.9): 15-25 lbs total, 0.5-0.7 lbs/week
Obese (≥ 30): 11-20 lbs total, 0.4-0.6 lbs/weekExample Calculation
Result: BMI 22.3 (Normal) — Gain 25-35 lbs total
At 5'4" and 130 lbs, the pre-pregnancy BMI is 22.3, which falls in the normal category. The recommended total gain is 25-35 lbs. During the second and third trimesters, the target is 0.8-1.0 lbs per week. In kilograms, that is 11.5-16 kg total and 0.36-0.45 kg per week.
Tips & Best Practices
- Calculate your BMI before conception or at the first prenatal visit for the most accurate recommendation.
- The first trimester accounts for only about 1-4.4 lbs of total gain.
- Obese women still need to gain weight — the guidelines call for 11-20 lbs, not zero.
- For twin pregnancies, add approximately 12-15 lbs to each range.
- Focus on the quality of food rather than quantity — aim for nutrient-dense choices.
- Regular prenatal visits help you stay on track with provider-guided adjustments.
BMI Categories and Pregnancy
Pre-pregnancy BMI is classified as underweight (< 18.5), normal (18.5-24.9), overweight (25-29.9), or obese (≥ 30). Each category has a specific recommended weight gain range that balances fetal growth needs with maternal health considerations.
Weekly vs. Total Gain
Total weight gain is the headline number, but weekly gain rate is more actionable for day-to-day management. The weekly rates apply primarily to the second and third trimesters, when fetal growth is most rapid. First-trimester gain is minimal and highly variable.
Setting Realistic Goals
Discuss your weight gain target with your provider at the first prenatal visit. Write it down. At each subsequent visit, your provider will track your actual gain against the target. If you fall outside the range, dietary counseling or additional monitoring may be recommended.
Sources & Methodology
Last updated:
Frequently Asked Questions
Women with different starting BMIs have different metabolic needs and risks. Underweight women benefit from more weight gain to support the baby, while obese women already have energy reserves and excessive gain adds risk for complications like gestational diabetes.
If your BMI is near a boundary (e.g., 24.8 or 25.1), discuss with your provider. They may recommend a target in between the two ranges based on your overall health profile.
The IOM guidelines were published in 2009 and have been widely validated. Some researchers suggest adjustments for higher BMI categories, but as of 2026, these remain the official recommendations endorsed by ACOG.
The IOM uses a single category for all BMI ≥ 30. Some providers recommend lower targets (10-15 lbs) for very obese women. This should be individualized with your care team.
Divide pounds by 2.2 to get kilograms. For example, 25 lbs is about 11.3 kg and 35 lbs is about 15.9 kg. The calculator shows both units.
Exercise is encouraged during pregnancy and may help you gain within the recommended range. It does not change the target itself, but it improves cardiovascular fitness, mood, and postpartum recovery.
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