Healthy pregnancy weight-gain ranges by pre-pregnancy BMI and trimester — Institute of Medicine guidelines. ✓ IOM guidelines
By pre-pregnancy BMI, per Institute of Medicine guidelines.
| Pre-pregnancy category | BMI | Total gain | Rate (2nd & 3rd trimester) | Twins |
|---|---|---|---|---|
| Underweight | Below 18.5 | 28–40 lb | 1.0–1.3 lb/week | 50–62 lb |
| Healthy weight | 18.5–24.9 | 25–35 lb | 0.8–1.0 lb/week | 37–54 lb |
| Overweight | 25.0–29.9 | 15–25 lb | 0.5–0.7 lb/week | 31–50 lb |
| Obese | 30.0 and above | 11–20 lb | 0.4–0.6 lb/week | 25–42 lb |
First-trimester gain is small for everyone — about 1–4.5 lb total. Most gain happens in the second and third trimesters at the weekly rate shown.
Recommended weight gain depends on your weight before pregnancy. A woman at a healthy pre-pregnancy BMI (18.5–24.9) is advised to gain about 25–35 pounds for a single baby, while someone who began underweight should gain more (28–40 lb) and someone overweight or obese less (11–25 lb). Gaining within your range supports your baby's growth while lowering the risk of complications for both of you.
Most of the gain comes in the second and third trimesters — often around a pound a week for a healthy-weight woman — while the first trimester adds only a few pounds. Carrying twins calls for more. To find your pre-pregnancy BMI category, use our BMI calculator, and track key dates with the pregnancy calculator and due date calculator.
Pregnancy weight-gain guidance is not a single number because the recommended range varies with pre-pregnancy BMI. A person starting underweight is advised to gain more than one starting overweight, and the ranges are set to balance risks that run in both directions — too little gain is associated with low birth weight, too much with delivery complications.
The distribution across pregnancy matters as much as the total. Gain in the first trimester is typically small, with most accumulating in the second and third, so a chart's endpoint says little about whether a given week is on track. Rate of gain is the quantity clinicians actually watch.
It also helps to know that the gain is not mostly fat. A substantial share is the baby, placenta, amniotic fluid, increased blood volume and breast tissue — components that resolve at or shortly after delivery. That composition is why the figures are not comparable to weight change outside pregnancy, and why any individual plan belongs with a clinician rather than a chart.