How pregnancy weight gain calculator works
Healthy pregnancy weight gain depends on your pre-pregnancy BMI and whether you are carrying one baby or twins. The US Institute of Medicine (IOM) guidelines give a recommended total gain range: for a singleton, underweight (BMI <18.5) aims for 28-40 lb, normal weight (18.5-24.9) for 25-35 lb, overweight (25-29.9) for 15-25 lb, and obese (30+) for 11-20 lb.
Gain is not spread evenly. The first trimester typically adds only 0.5-2 kg (1-4 lb) total. From the second trimester on, gain becomes a steady weekly rate — about 1 lb/week for a normal-BMI singleton, less for higher BMI categories. This calculator turns those rates into a running target so you can see how much gain is expected at your current week.
Enter your pre-pregnancy weight and height (so the tool can compute your BMI), your current gestational week, and whether it is a singleton or twin pregnancy. The tool reports your BMI category, the recommended total gain, the weekly rate, the first-trimester baseline, and your expected gain so far — in both kilograms and pounds. This is general guidance, not medical advice; your provider may set a personalised target.