What guidelines does this calculator use?

This tool follows the 2009 Institute of Medicine (IOM) / National Academies gestational weight gain guidelines, which are the standard reference used by OB-GYNs and midwives in the United States.

How is my BMI category determined?

BMI is calculated from your pre-pregnancy height and weight. Underweight is below 18.5, normal weight is 18.5–24.9, overweight is 25–29.9, and obese is 30 or higher. Each category has its own recommended total gain range.

What are the IOM weight gain recommendations?

For a singleton pregnancy: underweight women should gain 28–40 lb, normal weight 25–35 lb, overweight 15–25 lb, and obese 11–20 lb. Twin pregnancies have higher targets: normal weight 37–54 lb, overweight 31–50 lb, obese 25–42 lb.

How is weight gain distributed across trimesters?

The first trimester (weeks 1–12) typically accounts for only 1–4.5 lb (0.5–2 kg) of total gain. The second and third trimesters involve a steady weekly gain — roughly 0.5 lb/week for obese women up to about 1 lb/week for underweight women.

Does this replace advice from my doctor?

No. This tool is for educational reference only. Every pregnancy is unique. Always discuss your specific weight gain goals and nutritional needs with your healthcare provider.

What if I am already partway through my pregnancy?

Enter your current gestational week in the progress tracker section. The calculator shows how much you should have gained by now and how much remains, so you can compare against your actual weight.

Pregnancy Weight Gain Calculator

Name: Pregnancy Weight Gain Calculator
Availability: InStock
Author: Nham Vu

Enter your pre-pregnancy height and weight to get personalized total and weekly weight gain targets based on IOM guidelines.

Pre-Pregnancy Information

Unit System

Height

Pre-Pregnancy Weight lb

Carrying twins / multiples

Current Gestational Week (optional, 1–40)

Enter your details and click Calculate to see your personalized weight gain targets.

Summary

Enter your pre-pregnancy height and weight to get personalized total and weekly weight gain targets based on IOM guidelines.

How it works

Select your unit system (imperial or metric).
Enter your pre-pregnancy height and weight.
If carrying twins, check the multiple pregnancy box.
Click "Calculate" to see your BMI category and recommended weight gain ranges.
Review the trimester breakdown and current progress tracker.

Use cases

Understand how much weight is healthy to gain during your pregnancy.
Track whether your current weight gain is within recommended ranges.
Plan nutrition goals for each trimester.
Discuss personalized targets with your OB-GYN or midwife.
Compare singleton vs. twin pregnancy weight gain recommendations.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu