How to calculate pregnancy weight
BMI = weight ÷ height² × 703, then look up the IOM range for that BMI category
Worked example. Recommended gain: 25–35 lb.
Example inputs — Height (inches): 65; Pre-pregnancy weight (lb): 140; Carrying twins?: No. Starting values are illustrative.
Pre-pregnancy BMI 23.3 (normal weight) — IOM guidelines
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
The Institute of Medicine recommends different gain ranges depending on your pre-pregnancy BMI. Most gain happens in the second and third trimesters.
Assumptions & limitations
- Results are rounded for display.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
What if I'm outside the range?
Talk to your provider — they can tailor guidance to your health and pregnancy.