Pregnancy Weight Gain Calculator

The calculator computes BMI from your pre-pregnancy weight and height, then looks up the matching range from the Institute of Medicine's 2009 guidelines, endorsed by ACOG: underweight (BMI below 18.5) targets 12.7-18.1 kg, normal (18.5-24.9) targets 11.3-15.9 kg, overweight (25-29.9) targets 6.8-11.3 kg, and obese (30+) targets 5.0-9.1 kg. A lower starting BMI gets a higher target range, and vice versa.

The IOM pattern calls for only 0.5-2 kg total across the entire first trimester, then a steady weekly rate (specific to your BMI category, roughly 0.17-0.58 kg/week) from week 13 onward. That's why the calculator doesn't expect a straight-line share of your full-pregnancy total this early — gaining little in the first trimester is normal, not a sign anything is wrong.

The calculator compares your current weight minus your pre-pregnancy weight against the expected gain for your current week, using the first-trimester-then-weekly-rate pattern. Falling outside that range for a single check-in isn't itself a diagnosis — but if it's a consistent pattern, it's worth raising with your midwife or doctor rather than trying to correct it yourself, since dieting during pregnancy isn't recommended.

No. These ranges are for a single baby only. Twin pregnancies have separate, generally higher recommended ranges — roughly 17-25 kg at a normal pre-pregnancy BMI, per the IOM — and the IOM states there isn't enough evidence to set specific ranges for triplets or more. If you're carrying multiples, use your maternity team's figures instead of this calculator's output.

No — dieting or intentionally restricting calories during pregnancy isn't recommended, since it can limit nutrients your baby needs. These ranges are population guidance for monitoring, not targets to actively diet toward. If your gain is trending above range, the appropriate step is a conversation with your provider about nutrition quality and activity, not calorie restriction on your own.