Pregnancy Weight Gain Calculator
Find the total weight gain recommended across a full pregnancy from your pre-pregnancy weight and height — no need to know your BMI in advance. The calculator works out your pre-pregnancy body mass index (BMI) for you and shows it alongside the result. The figures come from the Institute of Medicine's 2009 guidelines for a singleton pregnancy, which set a different recommended range for each BMI category. The right amount of gain supports the baby's growth while limiting risks linked to gaining too little or too much; this calculator gives the range, and your provider tailors it to you.
Calculate
Default result: 25
Pregnancy Weight Gain Calculator · Result
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Recommended gain — low (lb)
132 lb × 63 in
- Recommended gain — high (lb)
- 35
- Pre-pregnancy BMI category
- normal
- Pre-pregnancy BMI
- 23.4
This calculator provides an estimate for general information only and is not medical advice. Due dates, gestational age, and fertility windows are estimates — babies rarely arrive exactly on the estimated due date, and individual cycles and pregnancies vary. Always confirm dates and any health decisions with your healthcare provider or OB-GYN.
Reviewed by the calculators.dev team · Last updated 2026-06-24
Formula reviewed against Institute of Medicine (2009) Weight Gain During Pregnancy: Reexamining the Guidelines; ACOG; PMC2847829
How to calculate
Enter the weight you were before pregnancy and your height — switch each between imperial and metric units with the unit toggle. The calculator computes your pre-pregnancy BMI (weight in kilograms ÷ height in metres squared), places it into one of four categories (underweight, normal, overweight, or obese), and returns the IOM 2009 recommended total gain range for that category. Your BMI is shown with the result so you can see exactly what your inputs produced.
First the pre-pregnancy BMI is computed as weight (kg) ÷ height (m)². The recommended total gain then depends on that BMI category (IOM 2009, singleton pregnancy): underweight (BMI under 18.5) → 28–40 lb; normal (18.5 to under 25) → 25–35 lb; overweight (25 to under 30) → 15–25 lb; obese (30 or more) → 11–20 lb.
Example calculation
Someone who weighed 60 kg (about 132 lb) at a height of 1.60 m (about 5 ft 3 in) has a pre-pregnancy BMI of 60 ÷ (1.60 × 1.60) = 60 ÷ 2.56 = 23.4, which falls in the normal-weight category (18.5 to under 25). For a singleton pregnancy, the IOM 2009 guidelines recommend a total weight gain of 25 to 35 pounds for this category.
- totalGainLowLb
- 25 lb
- totalGainHighLb
- 35 lb
- category
- normal
- bmi
- 23.4
Assumptions
- Ranges are the IOM 2009 recommendations for a singleton (one-baby) pregnancy. Twins and higher multiples have different, higher ranges not covered here.
- BMI categories use the standard WHO cut-points: underweight under 18.5, normal 18.5 to under 25, overweight 25 to under 30, and obese 30 or above.
- The figure is total gain across the whole pregnancy, not weekly. Most gain happens in the second and third trimesters.
- This is general guidance. Your provider sets a personal target based on your health, the baby's growth, and any conditions you have.
- A weight or height of zero or below is not valid and is reported as an error rather than a misleading range.
Common mistakes
- Entering your current pregnant weight instead of your pre-pregnancy weight. The ranges are keyed to the weight (and BMI) you started at.
- Mixing up the units — make sure the weight and height toggles match how you entered each value (e.g. lb with in, or kg with cm).
- Reading the range as a weekly target. It is the recommended total gain across the entire pregnancy.
- Applying the singleton ranges to a twin pregnancy, which has higher recommended gains.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. For a normal-weight start (BMI 18.5 to under 25), the IOM 2009 guideline is 25 to 35 pounds total for a singleton pregnancy. Other categories have different ranges.
Which BMI category am I in?
Underweight is a BMI under 18.5, normal is 18.5 to under 25, overweight is 25 to under 30, and obese is 30 or above. Enter your pre-pregnancy weight and height and the calculator works out your BMI and places you automatically — your BMI is shown with the result.
Is this for twins too?
No. These ranges are for a singleton pregnancy. Twin and higher-order pregnancies have separate, higher recommended ranges — ask your provider.
Is the recommended gain spread evenly?
No. Gain is usually small in the first trimester and picks up in the second and third. The figure here is the total across the whole pregnancy.