Pregnancy Weight Gain Calculator
Track your pregnancy weight gain against IOM guidelines. Supports single and twin pregnancies with week-by-week recommended ranges based on your pre-pregnancy BMI.
IOM
2009 Guidelines
BMI
Category-Based
Live
Your Status
Your Pregnancy Details
🏆
Weight Gained
8.0
kg so far
Ahead of Recommended Pace
23.9
Pre-Preg BMI
12–16
Total Rec.
8.0 kg
Gained So Far
4.5 kg
Rec. At This Week
5.8 kg
Still To Gain
Normal Weight
Pre-Preg BMI Category
📈 Week-by-Week Weight Gain Tracker
📋 IOM Recommended Weight Gain Guidelines
| Pre-Pregnancy BMI | Singleton Total | Twins Total |
|---|---|---|
| Underweight | 12.5–18 kg | 17–25 kg |
| Normal Weight | 11.5–16 kg | 17–25 kg |
| Overweight | 7–11.5 kg | 14–23 kg |
| Obese | 5–9 kg | 11–19 kg |
🧬 Where Does Pregnancy Weight Go?
A typical full-term pregnancy weight gain of ~12 kg breaks down into these components:
~3.4 kg
Baby
~0.7 kg
Placenta
~0.8 kg
Amniotic fluid
~0.9 kg
Uterus growth
~0.5 kg
Breast tissue
~1.8 kg
Blood volume
~1.5 kg
Body fluids
~3.4 kg
Fat stores
Understanding Pregnancy Weight Gain
Unlike most pregnancy tools that work off dates, healthy weight gain is driven by where you started — your pre-pregnancy BMI. Gaining too little is linked to a higher risk of preterm birth and low birth weight, while gaining too much raises the risk of gestational diabetes, pre-eclampsia, and a more difficult delivery. The IOM’s ranges exist to give you a realistic target band rather than a single number, because a healthy pace looks different for every starting body.
IOM Guidelines by Pre-Pregnancy BMI
Underweight (BMI < 18.5): 12.5-18 kg total · ~0.44-0.58 kg/week in 2nd & 3rd trimesterNormal weight (BMI 18.5-24.9): 11.5-16 kg total · ~0.35-0.50 kg/weekOverweight (BMI 25.0-29.9): 7-11.5 kg total · ~0.23-0.33 kg/weekObese (BMI ≥ 30): 5-9 kg total · ~0.17-0.27 kg/weekTwin pregnancy (add ~40-50%): Normal 17-25 kg · Overweight 14-23 kg · Obese 11-19 kgA note on precision: these ranges are population-level guidelines, not a strict prescription. Your OB/GYN or midwife will factor in your individual health history, how the pregnancy is progressing, and any complications — always treat their guidance as the final word over any calculator.
⚖️
Why BMI Matters
Your starting BMI reflects the energy reserves you're carrying into pregnancy. Lower reserves call for a larger gain to support the baby; higher reserves mean a smaller additional gain is enough, which is why the IOM sets a different target for each category.
👯
Twins Need More
Two placentas, roughly double the amniotic fluid, and a bigger blood volume expansion mean twin pregnancies need substantially more total gain — typically 40-50% above the singleton target at the same starting BMI.
📈
Gaining Too Fast
Rapid gain, especially in the third trimester, is linked to a higher risk of gestational diabetes, a larger-than-average baby, and a harder delivery. A sustained jump above the high line is worth mentioning to your provider.
📉
Gaining Too Slow
Consistently trailing the low line — often from nausea, reduced appetite, or under-eating — is associated with a higher risk of preterm birth and low birth weight. A week or two below the line usually isn't a concern; several weeks is.
— FAQ