Health Guide
Pregnancy Weight Gain Guidelines
The Institute of Medicine's recommended ranges depend on your pre-pregnancy BMI. The four bands, and how they're worked out.
Last updated: August 29, 2026
Recommended weight gain during pregnancy is not one figure — it depends on where your weight sat before pregnancy. This guide covers the published ranges and how your band is determined.
The recommended ranges
These come from the Institute of Medicine's 2009 report "Weight Gain During Pregnancy: Reexamining the Guidelines", and apply to single pregnancies:
| Pre-pregnancy BMI | Recommended total gain |
|---|---|
| Underweight (below 18.5) | 12.5 – 18 kg (28–40 lb) |
| Normal (18.5 – 24.9) | 11.5 – 16 kg (25–35 lb) |
| Overweight (25 – 29.9) | 7 – 11.5 kg (15–25 lb) |
| Obese (30 and above) | 5 – 9 kg (11–20 lb) |
The pattern is consistent: the higher the starting BMI, the lower the recommended gain. Our Pregnancy Weight Gain Calculator works out your band and range from your height and pre-pregnancy weight.
How your band is determined
Your band comes from your pre-pregnancy BMI — weight in kilograms divided by height in metres squared, exactly as covered in how BMI is calculated.
For someone 165 cm tall weighing 60 kg before pregnancy:
60 ÷ (1.65 × 1.65) = 60 ÷ 2.7225 = 22.0A BMI of 22.0 falls in the Normal band, giving a recommended gain of 11.5 – 16 kg.
One important detail about the cutoffs
These guidelines use the standard WHO BMI cutoffs, not the Asian-adjusted set that our BMI Calculator applies on the India regional pages.
That is deliberate on our part, not an oversight. The IOM guidelines were developed and validated against the standard cutoffs, so applying different thresholds to them would mean pairing one organisation's recommendations with another's classification — producing a figure neither body ever published. Where a guideline specifies its own basis, we follow that basis.
It does mean your BMI band here may differ from the band shown on our BMI calculator if you are using the India pages. Why India uses different BMI cutoffs explains that difference, which is real but belongs to a different question.
What the ranges are and aren't
These are population-level, evidence-based guidelines — a reasonable expectation for a typical single pregnancy, derived from outcome data across large groups.
They are not a target you have failed by missing. Gain is rarely even across a pregnancy, individual circumstances vary enormously, and the guidelines explicitly cover single pregnancies — if you are expecting more than one baby, different guidance applies and this calculator does not cover it.
Where the weight goes
It can help to know that gestational weight gain is not simply body fat. It includes the baby, the placenta, amniotic fluid, increased blood volume, larger breast and uterine tissue, and some fat stores. The ranges account for all of it.
The bottom line
Recommended gain depends on your pre-pregnancy BMI, running from 12.5–18 kg if you started underweight down to 5–9 kg if you started in the obese band. These are IOM population guidelines for single pregnancies, using standard BMI cutoffs. Check yours on the Pregnancy Weight Gain Calculator, and take anything that concerns you to your maternity team.
Keep reading
More in this guide series
Disclaimer: This guide is for general information only and is not medical advice, diagnosis, or treatment. Figures are estimates and typical ranges — for decisions about your health or pregnancy, consult a qualified healthcare provider.