Pregnancy weight gain calculator

Calculate your estimated healthy weight gain range based on your pre-pregnancy BMI, using IOM (2009) pregnancy weight gain guidelines as referenced by RANZCOG.

Check Your Healthy Range

Based on official IOM and RANZCOG clinical guidelines.

Please fill in all fields with valid, positive numbers.
Please note: This tool involves weight and body measurements during pregnancy. If you have a history of disordered eating or body image concerns, please speak with your GP, obstetrician, or midwife before using this tool. For eating disorder support, contact the National Alliance for Eating Disorders helpline.

*Estimates only. See full clinical & legal disclaimer below.

Understanding your pregnancy weight gain

Weight gain during pregnancy is a normal and expected part of a healthy pregnancy. The healthy range varies depending on your pre-pregnancy BMI, whether you are carrying multiples, and your individual medical situation. Your obstetrician, midwife, or GP is the best person to guide you on what is appropriate for you.

This calculator follows the official Institute of Medicine (IOM) guidelines, supported by the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). Rather than offering a generic number, it generates a personalised healthy target range based on your pre-pregnancy body type, based on population-level evidence from the IOM (2009) guidelines.

How is pregnancy weight gain calculated?

There is no one-size-fits-all number for pregnancy weight gain. Your ideal range depends on your pre-pregnancy Body Mass Index (BMI), which is calculated from your weight and height. The Institute of Medicine guidelines, recognised by the Royal Australian and New Zealand College of Obstetricians and Gynaecologists and widely used in Australian maternity care, recommend the following ranges for single pregnancies.

BMI category Pre-pregnancy BMI Single baby Twins
Underweight Below 18.5 12.5-18 kg 19-28 kg (twins)
Healthy weight 18.5-24.9 11.5-16 kg 17-25 kg (twins)
Overweight 25.0-29.9 7-11.5 kg 14-23 kg (twins)
Obese 30+ 5-9 kg 11-19 kg (twins)

Women carrying twins or multiples are advised to gain additional weight to meet the extra demands of a multiple pregnancy. If your pregnancy falls outside the standard guidelines, your doctor, obstetrician, or midwife will guide you with personalised recommendations.

General Disclaimer: Estimates only. This calculator uses standard IOM/RANZCOG guidelines. Every woman’s body and pregnancy are unique. Recommended weight gain varies depending on pre-pregnancy BMI, ethnicity, pregnancy type, medical conditions, foetal growth and pregnancy complications. Always discuss your weight, diet, and health with your GP, obstetrician, or midwife.

Where does the extra weight actually go?

One fact that surprises many first-time mothers is that only a small amount of pregnancy weight is maternal fat. Most of it comes from your growing baby and the remarkable changes your body undergoes to nurture and support pregnancy. Here’s a breakdown of where a typical 11.5 to 16 kg goes in women with a healthy pre-pregnancy Body Mass Index:
Component Approx. Weight What it Represents
Baby ~3.5 kg Largest single contributor
Placenta ~0.7 kg Nourishes and protects your baby
Amniotic fluid ~0.9 kg Cushions and supports the baby
Uterus enlargement ~0.9 kg The uterus expands considerably
Maternal breast tissue ~0.9 kg Preparation for breastfeeding
Increased blood volume ~1.8 kg Blood volume rises by up to 50%
Fluid in maternal tissue ~1.8 kg Normal pregnancy fluid retention
Maternal fat stores ~3.0 kg Essential energy reserves for breastfeeding
Total (approx.) ~13.5 kg Within a healthy-weight range
This breakdown is an important reminder that pregnancy weight gain has a clear purpose. Your body is not simply storing extra fat; it is building a placenta, expanding a uterus, nurturing your growing baby, and storing nutrients to help with breastfeeding later on.

Trimester-by-trimester weight gain

Weight gain in pregnancy does not happen at the same pace throughout the nine months. It tends to vary from one trimester to the next, and understanding what to expect at different stages can make these changes feel more comfortable with your body’s progress.
First trimester (weeks 1-12): Most women gain very little weight in the first trimester, usually around 1 to 2 kg in total. This is completely normal, as the baby is still very small (about the size of a lemon) at 12 weeks, and most of the weight gain comes later in pregnancy. In fact, some women lose a small amount of weight early in pregnancy due to morning sickness or reduced appetite. This is usually not concerning unless vomiting is severe and persistent.
Second trimester (weeks 13-26): This is the stage when your baby starts growing rapidly, and your body begins to change more visibly. From around week 13, most women begin gaining weight more steadily, usually about 0.3 to 0.5 kg per week, depending on their starting BMI. Underweight women may be advised to gain weight at a higher end of this stage, while those who are overweight may be advised to gain a little less.
Third trimester (weeks 27-40): Weight gain often continues at a similar pace in the third trimester, though some women may experience a natural slowdown in the final weeks as the baby drops into the pelvis. Many women also notice swelling in the feet, legs, or hands, which is common, though sudden or severe swelling should be reported to your doctor or midwife.

Why healthy weight gain matters in Australia

Pregnancy weight goals are not about appearance; it’s about supporting the best possible health outcomes for both you and your baby. Australian maternity guidelines emphasise that both inadequate and excessive weight gain can affect health.

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Gaining too little weight

  • Premature birth (born before 37 weeks)
  • Low birth weight, which can affect the infant’s long-term health and development
  • Difficulty establishing breastfeeding

↗
Gaining too much weight

  • Gestational diabetes
  • High blood pressure and pre-eclampsia
  • Macrosomia (a very large baby), which may complicate birth
  • Requiring a caesarean or instrumental delivery
  • Postpartum weight retention

If your weight gain is not within the recommended range, talk to your GP, obstetrician, or midwife. Simple changes to your diet and activity can help, and your care team can guide you based on your individual needs.

4 tips for managing weight gain during pregnancy

Healthy pregnancy weight gain is about nourishing yourself and your baby, not about dieting or restriction. Here are four evidence-based tips to help you stay on track:
1. Eating for two is a myth: Most women only need about 300 to 400 extra calories each day, and mainly during the second and third trimesters. In the first trimester, your calorie needs stay mostly the same. Focus on quality (healthy, nourishing food) over quantity.
2. Focus on nutrient density: Prioritise nutrient-rich foods rather than counting calories. Lean proteins, complex carbohydrates, leafy greens, iron-rich foods, calcium, and folate are essential for a healthy pregnancy diet. Limit processed foods and sugary drinks, which can contribute to weight gain with little benefit.
3. Stay active: Stay active during pregnancy unless your doctor or midwife advises against it. The Australian Department of Health recommends at least 30 minutes of moderate exercise on most days, such as walking, swimming, or prenatal yoga. Always check with your healthcare provider before starting an exercise routine.

4. Don’t obsess over the scale: Weighing yourself every day can lead to unnecessary stress, without offering much useful information. Checking your weight once a week is enough, or you can let your doctor or midwife monitor it during your scheduled appointments.

Pregnancy weight gain FAQs

It depends on your pre-pregnancy BMI. Women with a healthy pre-pregnancy weight (BMI 18.5-24.9) should aim to gain 11.5 to 16 kg in total. 

Most women gain very little weight in the first trimester. Consistent weight usually begins in the second trimester, from around 13 weeks.

Yes. Mild weight loss is common due to morning sickness, nausea, vomiting, or food aversions.

You do not need any extra calories in the first trimester. From the second trimester, most women need approximately 340 extra calories per day, increasing to around 450 extra calories in the third trimester. In the first trimester, calorie needs stay mostly the same. Focus on quality — healthy, nourishing food — over quantity. These figures apply to women carrying a single baby. Women carrying twins will need more.

If you started at a healthy BMI, the usual recommendation is between 17 and 25 kg. Women who are overweight (BMI 25-29.9) are often advised to gain 14 to 23 kg, and women who are obese (BMI 30+) should aim for 11 to 19 kg.

No. Weight loss dieting is not recommended during pregnancy. Limiting calories or nutrients can affect your baby’s growth.

Rapid weight gain in the third trimester is quite normal and usually occurs as your baby grows and your body holds more fluid. However, sudden or severe weight gain accompanied by headache, swelling, or blurred vision requires urgent medical attention.

A pregnancy BMI calculator is a tool to calculate your Body Mass Index from your height and pre-pregnancy weight.

Most women lose approximately 5 to 6 kg immediately after giving birth. This accounts for the weight of the baby, the placenta, and the amniotic fluid. The remaining weight gained during pregnancy gradually reduces over weeks and months following birth, especially with breastfeeding.

Yes. If severe morning sickness, nausea, vomiting, or fatigue make work difficult, you are entitled to a medical certificate to support your absence, if clinically appropriate after assessment. You can obtain one quickly and conveniently through a telehealth consultation with Hola Health.

An AHPRA-registered practitioner will assess your symptoms, provide appropriate advice, and issue a medical certificate if clinically appropriate.

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Medically reviewed by

MBBS, FRACGP, General Practitioner, 30+ Years of Experience

Disclaimer
Emergency: If you experience heavy bleeding, severe abdominal pain, reduced foetal movements, sudden swelling, or any other pregnancy emergency — call 000 immediately or go to your nearest emergency department. Do not use telehealth for emergency presentations.

Clinical Disclaimer: This calculator provides general estimates based on Institute of Medicine (IOM) guidelines. It does not account for all individual health factors and is not a substitute for personalised advice from your obstetrician, midwife, or GP. Always discuss weight management during pregnancy with your healthcare team.

Clinical Scope Disclaimer: This calculator provides estimates only based on standard biological timelines (such as typical menstrual cycles or average gestational parameters). It is not a diagnostic tool and cannot confirm pregnancy, conception dates, or fertility status.

Important: Hola Health operates strictly as a general primary care telehealth platform and does not provide specialised pregnancy, obstetric, or conception management services. For these services, patients must consult an in-person GP, obstetrician, or a dedicated fertility clinic.

References

  1. Guidance for healthy weight gain in pregnancy – reference link
  2. Management of obesity in pregnancy – reference link
  3. Evidence-based physical activity guidelines for pregnant women – reference link

Pregnancy symptoms taking a toll?

If severe morning sickness, fatigue, or nausea are making you dull and unfit for work, book a telehealth consult with Hola Health. Speak to an AHPRA-registered practitioner to discuss your symptoms, get advice, or request a medical certificate from the comfort of your home.

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If you have a history of an eating disorder, significant anxiety about weight, severe nausea or vomiting, diabetes, high blood pressure, fetal growth concerns, or a complex pregnancy, discuss weight gain with your GP, midwife or obstetrician rather than relying on a calculator.

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