Are you on track with recommended pregnancy weight gain?

How much weight should I gain during pregnancy?

The Institute of Medicine (IOM) recommends total gain ranges based on your pre-pregnancy BMI, for a single-baby pregnancy carried to term: 28-40 lbs if underweight (BMI under 18.5), 25-35 lbs if normal weight (18.5-24.9), 15-25 lbs if overweight (25-29.9), and 11-20 lbs if obese (30+). This calculator estimates roughly 2 lbs of that total by week 13, then spreads the remainder evenly across weeks 14-40.

Does starting BMI affect the recommendation?

Yes — the IOM guidelines are explicitly tiered by pre-pregnancy BMI category, with a lower starting weight linked to a higher recommended total gain and a higher starting weight linked to a lower one. This calculator computes your pre-pregnancy BMI first (the same formula as the BMI Calculator) to select the right range automatically.

What if I'm gaining faster or slower than recommended?

Individual pregnancies vary, and short-term fluctuations week to week are normal — this calculator gives a general population-level guideline, not a diagnosis or a strict target. If you're consistently outside the recommended range over several weeks, talk to your doctor or midwife, who can factor in your specific health history, nutrition, and how the pregnancy is progressing.

Does this apply to twin pregnancies?

No — the IOM sets separate, higher weight gain guidelines for twin and other multiple pregnancies, reflecting the additional physiological demands of carrying more than one baby. This calculator uses the singleton (single-baby) ranges only, so expecting parents of twins or multiples should get guidance specific to their pregnancy from their provider rather than relying on this tool.

Worked example: pre-pregnancy height 165 cm, weight 67 kg: BMI = 67 ÷ 1.65² ≈ 24.6, which falls in the Normal category (25-35 lbs total recommended). By week 20 — 7 weeks into the second-trimester phase after week 13 — the gain-to-date estimate is roughly 2 + (23 × 7÷27) to 2 + (33 × 7÷27) ≈ 8.0-10.6 lbs.