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Pregnancy Weight Gain Calculator

This calculator provides recommended weight gain targets during pregnancy based on your pre-pregnancy BMI. The guidelines follow the Institute of Medicine (IOM) 2009 recommendations, which are endorsed by Australian clinical practice guidelines for pregnancy care published by the Australian Government Department of Health.

Enter your details

Pre-pregnancy Weight

Height

Current Week of Pregnancy

weeks

Your Pregnancy Weight Gain Targets

Example

Example figures, not your own. Worked for someone 65 kg and 165 cm before pregnancy, at week 20. Enter your own details and press Calculate.

Pre-pregnancy BMI

23.9

Normal weight

Recommended Total Gain

11.5 – 16kg

Over the full pregnancy

Expected Gain by Week 20

3 – 5.2kg

Based on your current week of pregnancy

Weekly Gain (Trimester 2 & 3)

0.36 – 0.45kg/week

From week 14 onwards

Expected Gain by Trimester

First Trimester (Weeks 1-13)

0.5 – 2 kg

Second Trimester (Weeks 14-27)You are here

5.5 – 8.3 kg

Third Trimester (Weeks 28-40)

11.5 – 16 kg

Where Does Pregnancy Weight Go?

Baby3.0 – 3.5 kg

Placenta0.5 – 1.0 kg

Amniotic fluid0.8 – 1.0 kg

Uterus growth0.9 – 1.0 kg

Breast tissue0.5 – 1.4 kg

Blood volume1.2 – 1.8 kg

Body fluid1.0 – 2.5 kg

Fat stores2.0 – 4.0 kg

How It Works

Your pre-pregnancy BMI determines your recommended total weight gain range: Underweight (BMI < 18.5): 12.5-18 kg, Normal weight (BMI 18.5-24.9): 11.5-16 kg, Overweight (BMI 25-29.9): 7-11.5 kg, Obese (BMI 30+): 5-9 kg. Weight gain is minimal in the first trimester (0.5-2 kg total) and then approximately 0.4-0.5 kg per week in the second and third trimesters for normal-weight women.

How to use it

1Enter your pre-pregnancy weight in kilograms
2Enter your height in centimetres
3Enter your current week of pregnancy (1-42)
4Click "Calculate" to see your recommended weight gain range and trimester breakdown

Quick Reference

Pre-pregnancy BMI	Category	Total Gain (kg)	Weekly Gain T2/T3 (kg)
< 18.5	Underweight	12.5 – 18.0	0.44 – 0.58
18.5 – 24.9	Normal weight	11.5 – 16.0	0.36 – 0.45
25.0 – 29.9	Overweight	7.0 – 11.5	0.23 – 0.33
30.0+	Obese	5.0 – 9.0	0.17 – 0.27

Based on IOM 2009 guidelines, endorsed by Australian clinical practice guidelines for pregnancy care. T2/T3 = second and third trimesters.

Pregnancy Weight Gain Guidelines

Pre-pregnancy BMI = weight (kg) / height (m)^2 First trimester: 0.5 – 2.0 kg total Second & third trimesters: weekly rate based on BMI category

BMI < 18.5: = underweight - recommended total gain 12.5-18 kg
BMI 18.5-24.9: = normal weight - recommended total gain 11.5-16 kg
BMI 25-29.9: = overweight - recommended total gain 7-11.5 kg
BMI 30+: = obese - recommended total gain 5-9 kg

These guidelines apply to singleton pregnancies. Twin pregnancies have higher recommended gains. Always discuss your weight gain with your obstetrician or midwife.

Frequently Asked Questions

How much weight should I gain during pregnancy?

It depends on your pre-pregnancy BMI. Women with a normal BMI (18.5-24.9) are advised to gain 11.5-16 kg total. Underweight women should gain more (12.5-18 kg) and overweight women less (7-11.5 kg). These ranges are associated with the best outcomes for mother and baby.

When does most pregnancy weight gain occur?

Most weight gain happens in the second and third trimesters. In the first trimester, total gain is typically just 0.5-2 kg. From week 13 onwards, normal-weight women gain approximately 0.4-0.5 kg per week. Weight gain may slow slightly in the final weeks.

Is it safe to lose weight during pregnancy?

Intentional weight loss during pregnancy is generally not recommended. Even for women with obesity, the focus should be on gaining within the lower recommended range rather than losing weight. Always discuss weight management with your obstetrician or midwife.

What are these guidelines based on?

These recommendations follow the IOM 2009 guidelines, which are used in Australian clinical practice. They are based on extensive research linking maternal weight gain to outcomes for both mother and baby, including birth weight, caesarean delivery rates, and postpartum weight retention.

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