Pregnancy Weight Gain Calculator (IOM Guidelines)
Calculate recommended pregnancy weight gain targets based on pre-pregnancy BMI using the 2009 Institute of Medicine guidelines.
Results
What is it?
DISCLAIMER: For educational and reference purposes only. All clinical decisions must be made by qualified healthcare professionals. This calculator uses the 2009 Institute of Medicine (IOM) guidelines for gestational weight gain. Recommended ranges by pre-pregnancy BMI: Underweight (BMI <18.5): 12.5-18 kg total; Normal weight (BMI 18.5-24.9): 11.5-16 kg; Overweight (BMI 25-29.9): 7-11.5 kg; Obese (BMI >=30): 5-9 kg. These ranges are based on singleton pregnancies — twin and higher-order multiples have different recommendations.
How to use
Enter pre-pregnancy weight in kg, height in cm, and current gestational week. The calculator computes pre-pregnancy BMI, the IOM-recommended total gain range, and an approximate recommended cumulative gain at the current week of pregnancy (using a simplified linear model based on the weekly rate for the 2nd and 3rd trimesters).
Example scenario
Height: 165 cm. Pre-pregnancy weight: 65 kg. BMI = 65 / (1.65)^2 = 23.9 (normal weight). IOM range: 11.5-16 kg total. Weekly rate: 0.45 kg/week. At week 20: recommended gain = 0.45 x 20 = 9 kg. The actual IOM recommendation for the first trimester is approximately 0.5-2 kg, then ~0.45 kg/week — so 9 kg at week 20 is a reasonable approximation.
Pro tip
Weight gain in pregnancy is highly individual and should be monitored by an obstetric provider at each antenatal visit. The recommended weekly rate applies mainly to the 2nd and 3rd trimesters. Nausea in the first trimester may cause initial weight loss in some women, which is normal. This calculator uses a simplified linear model — the actual IOM recommendations account for trimester-specific patterns.