Calculate recommended pregnancy weight gain based on your pre-pregnancy BMI, following IOM guidelines. Track actual vs. expected weight gain by week.
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Recommendations based on Institute of Medicine (IOM) guidelines. Consult your healthcare provider for personalized advice.
Pre-BMI = weight(kg) / height(m)² | Recommended gain based on IOM BMI categoryPre-BMIBody Mass Index before pregnancyIOMInstitute of Medicine weight gain guidelinesTrimester 1≈ 1–2 kg total gain in first 13 weeksTrimester 2–3≈ 0.4–0.5 kg/week for normal BMIThe Institute of Medicine (IOM) recommends different total weight gain ranges based on pre-pregnancy BMI. Weight gain is generally slow in the first trimester and more rapid thereafter. This calculator uses linear interpolation to estimate expected gain at any given week.
Healthy pregnancy weight gain supports your baby's growth while reducing the risk of complications for both mother and child. The Institute of Medicine (IOM) provides evidence-based recommendations based on pre-pregnancy BMI, recognizing that one size does not fit all. This calculator applies those guidelines to your personal starting point.
Enter your pre-pregnancy weight, height, and unit system. The calculator computes your pre-pregnancy BMI, identifies your IOM weight gain category, and estimates the expected weight gain range for your current week of pregnancy. Optionally enter your current weight to see whether you are on track.
Pre-pregnancy BMI is 22.0 — 'normal weight', so the IOM range is 11.5–16 kg total.
By week 20, a gain of about 4–5 kg is on track for this BMI.
Gain is slow in the first trimester (~1–2 kg) then roughly 0.4–0.5 kg/week for a normal-BMI pregnancy.
The IOM total-gain range depends entirely on starting BMI.
Same pregnancy, very different healthy targets depending on where you start.
This tool gives you personalized week-by-week context — not just a final number, but whether your current gain is within the expected range for this point in your pregnancy. That context helps you have informed conversations with your healthcare provider.
A common mistake is comparing your gain to a friend's or to generic charts that don't account for starting BMI. Weight gain recommendations differ meaningfully between BMI categories — an underweight woman should gain considerably more than an obese woman. Always use your pre-pregnancy BMI as the reference point.
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