Pregnancy Weight Gain Calculator
See the healthy pregnancy weight-gain range for your pre-pregnancy BMI, and where you'd be expected to land by your current week, based on Institute of Medicine guidelines.
IOM weight-gain guidelines (single baby)
| Pre-pregnancy BMI | Recommended gain |
|---|---|
| Underweight (<18.5) | 28–40 lb (12.5–18 kg) |
| Normal (18.5–24.9) | 25–35 lb (11.5–16 kg) |
| Overweight (25–29.9) | 15–25 lb (7–11.5 kg) |
| Obese (30+) | 11–20 lb (5–9 kg) |
Pre-pregnancy 140 lb, 5'5" → BMI 23.3 (normal) → recommended 25–35 lb. By week 20, roughly 9–14 lb gained is typical.
Pre-pregnancy 80 kg, 165 cm, twin pregnancy. BMI = 80 ÷ 1.65² = 80 ÷ 2.7225 ≈ 29.4 — the "Overweight" category (25–29.9).
For twins at that BMI, the recommended total gain is 31–50 lb (about 14.1–22.7 kg) — noticeably more than the 15–25 lb recommended for an overweight BMI with a single baby. At week 28, roughly 10.8 kg (about 24 lb) gained would be typical, tracking along the steadier second/third-trimester rate described below.
How gain is distributed
Weight gain is meant to be gradual, not front-loaded: often just 1–5 lb in the first trimester, then about 0.5–1 lb per week through the second and third for a normal-BMI pregnancy. And it's not all baby — the placenta, amniotic fluid, extra blood, larger uterus, and breast tissue account for much of it. Pregnancy isn't the time for weight-loss dieting; even those starting at a higher weight are usually advised to gain some. These are general guidelines — your provider tailors them to your health. Check your starting BMI with the BMI calculator and track dates with the due date calculator.
IOM weight-gain guidelines (twin pregnancy)
| Pre-pregnancy BMI | Recommended gain (twins) |
|---|---|
| Normal (18.5–24.9) | 37–54 lb (16.8–24.5 kg) |
| Overweight (25–29.9) | 31–50 lb (14.1–22.7 kg) |
| Obese (30+) | 25–42 lb (11.3–19 kg) |
IOM guidance for twin pregnancies doesn't include a separate underweight recommendation, since there isn't enough research data to set one confidently — an underweight starting BMI with twins calls for closer, individualized guidance from your provider rather than a general range.
Common pregnancy weight-gain mistakes
- Applying singleton ranges to a twin pregnancy. As the table above shows, twin guidelines run meaningfully higher across every BMI category.
- Expecting gain to be linear from week one. The first trimester typically adds only 1–5 lb total; the steadier per-week rate applies mainly to the second and third trimesters.
- Reacting to a single week's fluctuation. Fluid retention can swing a weekly weigh-in by a pound or two either way — the multi-week trend is what matters, not any one reading.
Frequently asked questions
How much weight should I gain?
By pre-pregnancy BMI: underweight 28–40 lb, normal 25–35, overweight 15–25, obese 11–20 (single baby).
How is the gain distributed?
Little in trimester one, then ~0.5–1 lb/week. Baby is only part; placenta, fluid, and blood make up the rest.
Can I diet while pregnant?
No — pregnancy isn't for weight-loss dieting. Focus on nutrient-dense food and provider guidance.
How much more should I gain with twins?
Meaningfully more — around 37-54 lb for a normal BMI with twins, versus 25-35 lb for a single baby at the same BMI.
Is pregnancy weight gain linear from week one?
No — the first trimester adds relatively little (1-5 lb total), with a steadier per-week rate through the second and third trimesters.
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Medical disclaimer: General IOM guidelines, not personalized medical advice. Your obstetric provider sets the right target for your pregnancy and health. Guidelines: Institute of Medicine (2009). Last reviewed: September 2026.