Enter your pre-pregnancy weight, height and pregnancy week to see a weight-gain range for one baby or twins, plus an approximate range for your current week.
Pregnancy Weight Gain Calculator
Based on 2009 IOM Guidelines
* Weekly gain is approximate. Twin ranges are provisional; no IOM target is established for underweight twin pregnancies.
How much weight should I gain?
The amount of weight you should gain depends entirely on your Body Mass Index (BMI) before you got pregnant. There is no "one size fits all" number.
According to the 2009 IOM guidelines used by most obstetricians:
- Underweight (BMI < 18.5): 28–40 lbs (12.5–18 kg)
- Normal Weight (BMI 18.5–24.9): 25–35 lbs (11.5–16 kg)
- Overweight (BMI 25–29.9): 15–25 lbs (7–11.5 kg)
- Obese (BMI ≥ 30): 11–20 lbs (5–9 kg)
Weight Gain with Twins
If you are carrying twins, your nutritional needs are higher. Our calculator adjusts automatically for multiple pregnancies, where the recommended gain typically ranges from 37 to 54 lbs (17–25 kg) for women with a normal BMI.
Where does the weight go?
It's not just fat! A significant portion of your pregnancy weight comes from the baby, placenta, amniotic fluid, and increased blood volume.
- Baby: ~7.5 lbs
- Placenta & Fluid: ~3.5 lbs
- Increased Blood & Fluids: ~7–8 lbs
- Uterus & Breasts: ~4 lbs
- Maternal Fat Stores: ~7 lbs (Essential for breastfeeding)
Methodology
BMI is pre-pregnancy weight in kilograms divided by height in meters squared. Unit changes convert the entered measurements. Total singleton ranges and second/third trimester rates follow the 2009 IOM/NRC report. Weekly values interpolate 0.5–2 kg through week 13, then apply a constant weekly rate. These are approximate progressions, not independent weekly targets. Twin total ranges are rounded provisional guidance; twin weekly rates are illustrative. The report found insufficient evidence for an underweight twin target; that scenario displays the normal-BMI twin range for comparison, not a recommendation. The model supports weeks 1–42; weeks 41–42 extend the same rate beyond term.