OmniCalcsPregnancy Weight Gain Calculator
See the IOM recommended gain for your pre-pregnancy BMI, and a target weight range at any week.
How to Use This Pregnancy Weight Gain Calculator
Enter height in centimeters, weight just before pregnancy in kilograms, and the current gestational week. The calculator reports BMI, the IOM total-gain band, and a target weight range for that week.
- Underweight (BMI under 18.5) — 12.5 to 18 kg over the full pregnancy.
- Normal (18.5 to 24.9) — 11.5 to 16 kg.
- Overweight (25 to 29.9) — 7 to 11.5 kg.
- Obese (30 and above) — 5 to 9 kg.
Practical Example
Height 165 cm, pre-pregnancy weight 60 kg, week 40:
- BMI = 60 / 1.65² ≈ 22.0 (normal)
- Recommended gain = 11.5–16 kg
- Target weight at term = 71.5–76 kg
What Your Results Mean
- Pre-pregnancy BMI — the category that selects the IOM band.
- Recommended total gain — the full-pregnancy range for a singleton pregnancy.
- Target this week — that range scaled by week/40, so week 20 is about halfway.
Twins, fluid shifts and your clinician's advice can differ. Use this as a guide, not a substitute for prenatal care.
Frequently Asked Questions
Where do these ranges come from?
The U.S. Institute of Medicine (now the National Academy of Medicine) 2009 guidelines for singleton pregnancies, still cited by CDC and ACOG.
Does gain happen evenly each week?
Not exactly. Many people gain little in the first trimester and more later. This tool spreads the band evenly to week 40 so you have a simple target, not a medical schedule.
What if I am expecting twins?
IOM twin ranges are higher (often about 17–25 kg for a normal BMI). This calculator is for one baby only.
Should I try to stay in the band every week?
Week-to-week weight jumps. Look at the trend with your clinician rather than any single reading.
Is this medical advice?
No. It restates published IOM ranges. Follow the plan from your obstetric provider.