Pregnancy Weight Gain Calculator

Enter your pre-pregnancy height, weight, and current week to see your recommended weight gain range.

How to Use the Pregnancy Weight Gain Calculator

Enter your pre-pregnancy height and weight — toggle to US units if that's easier — plus your current week of pregnancy, and the calculator returns your pre-pregnancy BMI category, your total recommended weight gain range, and a rough estimate of how much of that you should have gained by this point.

The recommended range comes from the 2009 Institute of Medicine guidelines — IOM, now folded into the National Academies of Sciences, Engineering, and Medicine — still the clinical standard reference doctors use today for singleton (single-baby) pregnancies. The guidelines don't hand out one number for everyone; they scale the target to pre-pregnancy BMI.

Underweight (BMI < 18.5):  28–40 lb (12.5–18 kg)
Normal weight (18.5–24.9): 25–35 lb (11.5–16 kg)
Overweight (25–29.9):      15–25 lb (7–11.5 kg)
Obese (30+):                11–20 lb (5–9 kg)

The logic behind the spread is straightforward once you see it: someone starting pregnancy underweight has less physiological reserve to draw on, so the guidelines push their target higher to support fetal growth adequately. Someone starting significantly overweight already carries more reserve, so their recommended range sits lower — though it's still a positive number. Pregnancy is never the time to target weight loss, regardless of starting BMI; even the obese-category range calls for real, if modest, gain.

The "estimate by this week" figure is a straight-line share of the total range — current week divided by 40, multiplied against the low and high end. Real pregnancy weight gain doesn't follow a straight line at all: the first trimester typically adds very little, and most of the gain concentrates in the second and third. This is the same weight-to-height ratio the standalone BMI Calculator uses — the only difference here is what happens with that number next: instead of a general weight classification, it becomes the starting point for a pregnancy-specific target. Clinicians typically check actual gain against this total range at each prenatal visit rather than expecting a smooth week-by-week climb, so don't read too much into any single week's number on its own.

This is a general estimate, not personalized medical guidance. Twin and multiple pregnancies follow separate, higher targets not covered here, and individual health conditions can shift what's appropriate. Talk to a doctor or a registered dietitian about the weight gain pattern that's right for your specific pregnancy.