Pregnancy Weight Gain Calculator
See your recommended pregnancy weight gain for the current week, based on your pre-pregnancy BMI and Institute of Medicine (IOM) guidelines — and check whether you are on track.
Pregnancy Details
0 = skip the on-track check
Recommended by Week 20
2.9–5.5 kg
Pre-pregnancy BMI 22.9 (Normal weight)
Pre-pregnancy BMI
22.9 (Normal weight)
Total Recommended Gain
11.5–16 kg
Recommended by Week 20
2.9–5.5 kg
Weekly Rate (2nd/3rd tri)
0.35–0.5 kg/wk
How It Works
Healthy weight gain in pregnancy depends on your pre-pregnancy BMI, and this calculator follows the widely-used Institute of Medicine (IOM) guidelines for a single baby. First it computes your pre-pregnancy BMI from your weight and height, which sets your recommended total gain: underweight 12.5–18 kg, normal 11.5–16 kg, overweight 7–11.5 kg, and obese 5–9 kg. Gain is not linear — most happens in the second and third trimesters. The first trimester adds only about 0.5–2 kg, after which a steady weekly rate applies (for a normal BMI, roughly 0.35–0.5 kg/week). Enter your current week to see the recommended gain-to-date range, and optionally your current weight to check whether you are below, within, or above the healthy band. Every pregnancy is different, so always follow your doctor’s or midwife’s guidance.
Formula
Pre-pregnancy BMI sets the total range (IOM). Recommended-to-date = first-trimester gain (~0.5–2 kg) + weeks after 13 × the weekly rate for your BMI category.
Frequently Asked Questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI (IOM guidelines): underweight 12.5–18 kg, normal 11.5–16 kg, overweight 7–11.5 kg, obese 5–9 kg — for a single baby. Twins have higher ranges.
When does most pregnancy weight gain happen?
In the second and third trimesters. The first trimester typically adds only about 0.5–2 kg; after that, weight rises at a steadier weekly rate that depends on your BMI category.
Is it based on pre-pregnancy or current weight?
Your recommended range is set by your pre-pregnancy BMI. Enter your pre-pregnancy weight and height for the BMI, then your current weight (optional) to check your gain so far against the target.
What if I am gaining too much or too little?
Both matter for you and your baby. This tool flags if you are outside the recommended band, but weight can fluctuate — discuss any concerns with your doctor or midwife rather than adjusting drastically on your own.
Are these guidelines suitable for twins?
These ranges are for a single baby. Twin pregnancies have higher recommended gains (for a normal BMI, around 17–25 kg). Follow your healthcare provider’s specific advice for multiples.