Pregnancy Weight Gain Calculator
0 lb gained so far
| Stage | Typical Weekly Gain | Cumulative Target |
|---|---|---|
| 1st Trimester (0-13 wk) | ||
| 2nd Trimester (14-27 wk) | ||
| 3rd Trimester (28-40 wk) |
How the Recommended Range Is Calculated
This calculator uses the Institute of Medicine (IOM, now the National Academy of Medicine) 2009 pregnancy weight gain guidelines, which set a target range based on pre-pregnancy BMI rather than a single number for everyone. Underweight (BMI under 18.5) mothers are advised to gain 28-40 lb, normal-weight (18.5-24.9) mothers 25-35 lb, overweight (25-29.9) mothers 15-25 lb, and obese (30+) mothers 11-20 lb over a full-term singleton pregnancy. For twins, the IOM published ranges shift upward: roughly 37-54 lb for normal weight, 31-50 lb for overweight, and 25-42 lb for obese pre-pregnancy BMI — the IOM did not publish a twin range for underweight mothers (the evidence was considered insufficient), so the figure this calculator shows for that combination is an extrapolation above the normal-weight twin range, not an official guideline; if this applies to you, lean on your OB-GYN's individualized guidance over this number. Pre-pregnancy BMI itself is the standard weight(kg)/height(m)² formula. If you don't know your pre-pregnancy BMI, the BMI calculator can help you find it from the same height and weight numbers.
Gain Isn't Linear, and That's Normal
Most of the recommended gain is expected to happen in the 2nd and 3rd trimesters — many people gain only 1-5 lb total in the first trimester, then close to a pound a week afterward. This calculator's week-by-week target divides your remaining recommended range evenly across the trimesters that haven't finished yet, so don't be alarmed if week-to-week gain looks uneven; short-term fluctuations from water retention, digestion, and appointment timing are completely normal and a single week's number matters far less than the overall trend.
An Estimate, Not a Diagnosis
This tool provides a general educational estimate based on population-level guidelines — it can't account for multiples beyond twins, pre-existing conditions, or how your individual pregnancy is progressing. Always discuss your weight gain pattern with your OB-GYN or midwife, who can weigh it against your specific medical history. If you're mapping out timing, the due date calculator can help you see where you are in the pregnancy at a glance.
Frequently Asked Questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. Per Institute of Medicine (IOM) guidelines, underweight mothers (BMI under 18.5) should aim for 28-40 lb total, normal-weight mothers (18.5-24.9) for 25-35 lb, overweight mothers (25-29.9) for 15-25 lb, and mothers with obesity (30+) for 11-20 lb. Twin pregnancies have higher targets in each category.
Why is most of the weight gain expected later in pregnancy?
The first trimester typically accounts for only a small share of total gain (often just a few pounds) because the fetus is still very small, while growth accelerates through the second and third trimesters. This calculator reflects that by allocating roughly 10% of the target to the first trimester and splitting the rest evenly across the second and third.