Pregnancy Weight Gain Calculator
Estimate your recommended total weight gain range and where you should be week-by-week, based on your pre-pregnancy BMI and IOM guidelines.
*Estimates only, for singleton pregnancies, not medical advice. Always follow guidance from your obstetrician or midwife.
🤰 Understanding Pregnancy Weight Gain
How the recommended ranges are calculated and why they change by trimester.
How it Works
Calculates your pre-pregnancy BMI from height and weight, then applies IOM (Institute of Medicine) recommended total gain ranges and weekly gain rates for that BMI category.
The Formula
BMI = Weight(kg) / Height(m)². First trimester gain is roughly flat (0.5-2kg total); after week 13, gain accrues at a BMI-specific weekly rate (e.g. 0.35-0.5 kg/week for normal BMI).
Pro Tip
Track weight trends over weeks rather than reacting to single readings — day-to-day fluctuations from fluid retention and food intake are completely normal.
Frequently Asked Questions
How much weight should I gain during pregnancy? +
It depends on your pre-pregnancy BMI. The Institute of Medicine (IOM) recommends 12.5-18kg for underweight women, 11.5-16kg for normal weight, 7-11.5kg for overweight, and 5-9kg for obese women carrying a single baby.
How much weight should I gain in the first trimester? +
Most guidelines suggest only 0.5-2kg total gain during the first trimester (weeks 1-13), regardless of starting BMI, since the fetus is still very small. The bulk of recommended weight gain happens in the second and third trimesters.
What if I'm gaining weight faster or slower than recommended? +
Occasional weeks above or below target are normal and not a cause for alarm. A consistent, significant deviation from the recommended range over several weeks should be discussed with your obstetrician or midwife, who can assess it alongside fetal growth and your overall health.
Do twin pregnancies follow the same weight gain guidelines? +
No. Twin pregnancies have higher recommended ranges — roughly 17-25kg for normal weight, 14-23kg for overweight, and 11-19kg for obese women. This calculator is designed for single (singleton) pregnancies only.
Where does pregnancy weight gain actually go? +
A typical breakdown for an 11.5-16kg gain includes roughly 3-3.5kg baby, 0.7kg placenta, 0.9kg amniotic fluid, 0.9kg breast tissue, 1.4kg blood volume, 2-4kg maternal fat stores, and 0.9-1.4kg increased fluid and uterus growth.
Is it safe to try to lose weight while pregnant? +
Intentional weight loss is generally not recommended during pregnancy, even for women who begin in the obese category, because the developing fetus depends on a steady nutrient supply. Any concerns about weight during pregnancy should be discussed directly with a healthcare provider.