Pregnancy Weight Gain Calculator is a free tool that checks healthy weight gain from your pre-pregnancy BMI using the Institute of Medicine 2009 ranges. Enter your height, weight before pregnancy and current week to get your total range and the expected band for this week. The maths runs in your browser; nothing is uploaded.
How to check pregnancy weight gain
- Enter Height and Weight before pregnancy — before, not today.
- Set Weeks pregnant now (find it with the Pregnancy Due Date Calculator if unsure).
- Read the Recommended total range for the whole pregnancy.
- Optionally add your Current weight for the on-track check against this week’s band.
A worked example: 165 cm, 60 kg, week 24
That is a BMI of 22.0 — normal weight — so the IOM range is 11.5 to 16 kg total. By week 24 the expected cumulative gain is 4.4 to 7.5 kg: the flat 0.5–2 kg of the first trimester plus eleven weeks at 0.35–0.5 kg a week. A current weight of 67 kg means 7 kg gained — inside the band, slightly above its middle, which is exactly where uneventful pregnancies usually sit.
Ranges, not targets — and why both ends matter
Gaining below the range is linked with small-for-gestational-age birth and preterm delivery; above it with large babies, caesareans and weight kept afterwards. Neither end is a verdict on one reading — midwives watch the trend across weeks. And deliberately losing weight is not recommended at any BMI during pregnancy. For the fitness side of the same journey, see what steady activity is worth in the TDEE Calculator.
Frequently asked questions
Why does only the pre-pregnancy BMI matter?
Because the Institute of Medicine ranges key off it alone: the same four bands decide the whole pregnancy’s range. Today’s weight tells you where you stand inside the range; it never changes which range applies.
I gained nothing in the first trimester. Is that a problem?
Usually not. The expected first-trimester gain is just 0.5 to 2 kg, and little or none is common — the steady weekly climb only starts around week 13. Persistent loss or vomiting that keeps food down needs a doctor, not a calculator.
What about twins?
This tool covers single pregnancies: twin ranges are higher and provisional, roughly 16 to 24 kg at normal BMI with faster weekly rates. With multiples, use your doctor’s targets instead of these bands.
Is this medical advice?
No. It applies the published IOM 2009 ranges to your numbers. Weight is one signal among many — blood pressure, glucose, growth scans and your history matter more — so review the result with your midwife or doctor.
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