Pregnancy Weight Gain by Week Calculator
Expected weight gain at your current pregnancy week from pre-pregnancy BMI (IOM guidelines), compared with what you have actually gained.
How it works
Gain by week = 0.5–2 kg in trimester 1 + weekly rate × (week − 13); rates and totals by BMI from IOM 2009
The Institute of Medicine sets total gain by pre-pregnancy BMI — 11.5–16 kg for a normal BMI, less when starting heavier — with most of it in the second and third trimesters at a steady weekly rate. Gains outside the range are common and often fine; a sudden jump of more than 1 kg in a week late in pregnancy should be checked for fluid retention.
Worked example
165 cm, 62 kg (BMI 22.8, normal) at 26 weeks: 0.5–2 kg + 13 × 0.35–0.5 = 5.1–8.5 kg expected; 6 kg gained is on track.
Frequently asked questions
Where does the weight go?
Baby ~3.5 kg, placenta and fluid ~1.5 kg, uterus and breasts ~2 kg, blood and fluid ~3 kg, fat stores 2–4 kg.
Should I diet if I am above the range?
No — slow the rate with food quality and activity rather than cutting calories; ask your midwife for a plan.
Related calculators
Educational estimate only — your midwife or doctor will confirm dates and advice for your pregnancy.