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BMI in Pregnancy and Breastfeeding
BMI is used as a starting point before pregnancy. It is not a tool to judge your weight while pregnant or breastfeeding.
Recommended weight gain by pre-pregnancy BMI
Typical totals for a single baby, based on Institute of Medicine guidance used in Australian antenatal care:
| Pre-pregnancy BMI | Total gain |
|---|---|
| Underweight (under 18.5) | 12.5 – 18 kg |
| Healthy weight (18.5 – 24.9) | 11.5 – 16 kg |
| Overweight (25 – 29.9) | 7 – 11.5 kg |
| Obesity (30 and over) | 5 – 9 kg |
Twins and higher multiples have different targets. Your care team will tailor advice to you.
After the baby
Weight changes gradually after birth, and that is normal. If you are breastfeeding, you need extra energy and nutrients, so avoid crash diets. Gentle activity and balanced meals are safer than rapid weight loss.
Once you are cleared by your GP, usually at the six-week check, you can use the BMI calculator as a rough guide.
Where to get support in Australia
- Pregnancy, Birth and Baby: free healthdirect service, 1800 882 436.
- healthdirect: 24-hour nurse advice on 1800 022 222.
- COPE: perinatal mental health support.
Pregnancy questions
Can I use a BMI calculator while pregnant?
BMI is not used to assess your weight during pregnancy. It is used at your first antenatal visit with your pre-pregnancy weight, and your midwife or doctor will advise how much weight gain suits you.
How much weight should I gain in pregnancy?
Recommended total gain depends on pre-pregnancy BMI: about 12.5 to 18 kg if underweight, 11.5 to 16 kg if healthy weight, 7 to 11.5 kg if overweight and 5 to 9 kg if obese (single baby). Your care provider will tailor this.
When can I use the calculator after having a baby?
Many women use it once they feel recovered, usually after the six-week check. Gentle changes over many months are safer than rapid weight loss, especially while breastfeeding.