Your healthy weight-gain range by pre-pregnancy BMI (2009 IOM guidelines)
Your weight before pregnancy — not your current weight. This sets your BMI.
Optional — check if you're on track
Gestational age in weeks. Enables the week-by-week check.
Today's weight, to compare your gain so far.
Recommended total weight gain
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Educational tool, not medical advice. This calculator uses the 2009 Institute of Medicine (IOM/NAM) guidelines reaffirmed by ACOG. It is for general information only and does not replace advice from your OB-GYN or midwife, who will personalize your target — especially with gestational diabetes, high blood pressure, prior bariatric surgery, eating disorders, very high BMI, or short stature. Twin ranges are provisional and based on more limited evidence; triplets and higher-order multiples are not covered. No data leaves your device.
Pregnancy Weight Gain Calculator — guide & how to use
What it does
This calculator gives you a personalized healthy weight-gain range for your whole pregnancy,
based on the single factor that drives the official guidelines: your pre-pregnancy BMI. It uses
the 2009 Institute of Medicine (IOM) recommendations, separates single babies from twins, and —
if you enter your current week and weight — shows whether your gain so far is on track, plus the
suggested weekly pace for the rest of the pregnancy. Everything is calculated privately in your browser, free.
How to use it
Choose your units and whether you're carrying a single baby or twins.
Enter your pre-pregnancy weight (not today's weight) and your height — together these set your BMI category.
Read your recommended total gain range at the top, with the BMI value and category below.
Optionally add your current week and current weight to see the expected gain by that week and an on-track status.
How the math works
BMI: weight (kg) ÷ height (m)². The unrounded BMI selects your category, so a value like 24.97 (shown as 25.0) is still classified as normal weight.
Expected gain by week W: the first-trimester band plus the weekly rate applied to weeks 14 through W (the curve is capped at 40 weeks).
Worked example
A woman who weighed 140 lb before pregnancy, is 5 ft 5 in (65 in) tall,
carrying one baby, and is now at 20 weeks weighing 150 lb:
BMI = 140 × 703 ÷ 65² = 23.3 → normal weight.
Total target (normal, singleton) = 25–35 lb.
Expected by week 20: first-trimester 1.1–4.4 lb + (20 − 13) weeks × 0.8–1.0 lb/wk = 1.1 + 5.6 to 4.4 + 7.0 = about 6.7–11.4 lb.
Actual gain so far = 150 − 140 = 10 lb → within the 6.7–11.4 lb band → on track.
Remaining to target = 25 − 10 to 35 − 10 = 15–25 lb over the ~20 weeks left → roughly 0.75–1.25 lb/week going forward.
Accuracy & safety notes
These are population guidelines for full-term, healthy pregnancies. Your provider may set a different target for your situation.
Use pre-pregnancy weight for BMI — using current weight inflates it and produces a target that is too low.
The week-by-week model is a simplification: real gain is uneven and early loss from nausea is normal. The "on track" band is a guide, not a pass/fail verdict.
Twin ranges are provisional; underweight twins has no official IOM range — we won't invent a number.
Triplets and higher-order multiples are out of scope — talk to your provider.
All computation is client-side — no health data leaves your device.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. For a single baby: underweight 28–40 lb, normal weight 25–35 lb, overweight 15–25 lb, obese 11–20 lb. Twins have higher provisional ranges.
Which weight do I use — pre-pregnancy or current?
Your pre-pregnancy weight, always, to set the BMI. Current weight is only for the optional on-track check. Using current weight gives a target that is too low.
How much should I have gained by a certain week?
About 1–4 lb in the first trimester, then a steady weekly rate set by your BMI (normal weight is about 0.8–1.0 lb/week). Enter your week to see the expected cumulative range.
How much weight should I gain with twins?
IOM provisional ranges: normal 37–54 lb, overweight 31–50 lb, obese 25–42 lb. There is no official range for underweight women with twins — ask your provider.
I've lost weight in early pregnancy — is that bad?
Early loss from nausea is common, especially in the first trimester. The tool will show a negative gain and gentle wording rather than an error. Mention significant loss to your provider.
Is it really free?
Yes. 100% free, everything runs privately in your browser.