Pregnancy Weight Gain Calculator
Compares your weight gain so far against Institute of Medicine recommendations based on pre-pregnancy BMI, current week and twins, with a week-by-week cumulative gain table and where the weight typically goes.
TheCalculators — Pregnancy Weight Gain Calculator
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Weight Gained So Far — Within recommended range
11.0 lb (5.0 kg)
Recommended by week 20: 3.6 kg – 6.2 kg
- Pre-pregnancy BMI
- 18.4 — Underweight
- Total recommended gain
- 12.7 kg – 18.1 kg
- Recommended by week 20
- 3.6 kg – 6.2 kg
- Weekly rate (2nd/3rd trimester)
- 0.5 kg – 0.6 kg/week
- First trimester target
- 1 – 4.5 lb (0.5 – 2 kg) total
- Remaining to upper limit
- 1.2 kg
Pre-pregnancy BMI
18.4kg/m²
Mild thinness
Where pregnancy weight goes (typical single pregnancy, lb)
- Baby7.50
- Fat stores7.00
- Blood volume3.50
- Fluid volume2.50
- Breasts2.00
- Uterus2.00
- Amniotic fluid2.00
- Placenta1.50
IOM recommended cumulative gain by week
Underweight 1–1.3, normal 0.8–1, overweight 0.5–0.7, obese 0.4–0.6 lb/week after week 13.
Gain varies naturally between women; a trend line matters more than any single week. Review gains with your prenatal provider. Estimates for informational purposes only — not medical advice.
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Formula
Recommended gain = 1–4.5 lb (1st trimester) + weekly rate × (week − 13) · weekly rate set by pre-pregnancy BMI (IOM)
- • Compute pre-pregnancy BMI = weight (kg) ÷ height (m)².
- • Select the IOM band: <18.5 → 28–40 lb total, 18.5–24.9 → 25–35 lb, 25–29.9 → 15–25 lb, ≥30 → 11–20 lb.
- • Add ~1 lb/week (0.8–1.0 normal BMI) for every week past week 13; twins use higher rates (37–54 lb normal BMI).
Pro tips
- • Only ~300 extra calories/day are needed in the 2nd/3rd trimester — "eating for two" is a myth.
- • Weigh at the same time of day, same scale, for a reliable trend.
- • Gaining too fast or too slow both warrant a conversation with your provider, not panic.
FAQ
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