Pregnancy Weight Gain Calculator
Recommended total gain by BMI category
| Pre-pregnancy BMI | Singleton | Twins |
|---|---|---|
| Underweight (<18.5) | 28–40 lb (12.7–18.1 kg) | Not established |
| Normal (18.5–24.9) | 25–35 lb (11.3–15.9 kg) | 37–54 lb (16.8–24.5 kg) |
| Overweight (25–29.9) | 15–25 lb (6.8–11.3 kg) | 31–50 lb (14.1–22.7 kg) |
| Obese (30+) | 11–20 lb (5.0–9.1 kg) | 25–42 lb (11.3–19.1 kg) |
How this is calculated
These ranges come from Institute of Medicine (IOM, now part of the National Academies of Sciences, Engineering, and Medicine) guidelines, the reference most widely used by care providers in the US and beyond. They're built around your pre-pregnancy BMI category — underweight, normal weight, overweight, or obese — on the idea that someone starting pregnancy with less reserve generally benefits from gaining more, and vice versa.
The "expected gain by this week" figure above is a smooth estimate, not a real week-by-week curve: it assumes a small, roughly flat gain through the first trimester followed by a steadier, near-linear pace through the second and third. Real pregnancies rarely gain in a straight line — some weeks bring more, some less, and that's normal.
Common edge cases and things to know
Twin (and higher-order multiple) pregnancies have their own, higher gain ranges, shown in the table above — and for underweight pre-pregnancy BMI carrying twins, there isn't yet an established guideline, so that's a conversation for your OB or maternal-fetal medicine specialist rather than a general chart.
Morning sickness, restrictive diets, gestational diabetes management, or a multiple pregnancy can all shift what "typical" gain looks like for you specifically. These ranges are population-level starting points — your own provider will track your actual gain against your own baseline and flag anything that needs attention, which matters far more than matching a chart exactly.
Gaining notably less than the recommended range, especially alongside reduced appetite or persistent nausea, and gaining notably more, especially with swelling or a sudden jump in a short period, are both things worth flagging at your next prenatal visit rather than waiting for your next scheduled check. Pre-pregnancy BMI itself is only ever a starting estimate too — it doesn't account for muscle mass, body composition, or individual metabolism, which is another reason these ranges are a guide rather than a strict target.