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Pregnancy Weight Gain Calculator

See your recommended weight gain range by week based on the IOM 2009 guidelines used by Australian obstetricians.

Your details

kg
4095150
cm
140165190
weeks
1132842

Pre-pregnancy BMI

26.0Overweight

Total recommended gain

7.0 – 11.5 kg

Gain to date (week 20)

2.1 – 4.3 kg

Weekly rate (2nd/3rd tri)

0.23 – 0.33 kg/wk

Goal weight at 40 weeks

77.0 – 81.5 kg

Recommended weight gain corridor

048120w10w20w30w40wkg

This calculator provides estimated weight gain ranges based on the IOM 2009 guidelines. It is not a substitute for professional medical advice. Always discuss weight gain with your midwife, GP, or obstetrician. If you have concerns, call Pregnancy, Birth and Baby on 1800 882 436.

What Is Pregnancy Weight Gain?

Pregnancy weight gain is the total weight a woman gains from conception to delivery. The baby accounts for only about 25 percent of total gain. The rest supports fetal development, builds necessary maternal tissue, and prepares the body for breastfeeding.[10, 11] How much you should gain depends primarily on your pre-pregnancy BMI, and both too little and too much carry risks for mother and baby.

ComponentApproximate weight
Baby3.0–3.6 kg
Placenta0.7 kg
Amniotic fluid0.8–0.9 kg
Uterus growth0.9 kg
Breast tissue0.4–1.4 kg
Increased blood volume1.2–1.8 kg
Extra body fluid0.9–1.5 kg
Maternal fat stores2.7–3.6 kg

The physiological components (everything except fat stores) account for approximately 8 to 10 kg. Fat stores serve as an energy reserve for breastfeeding and recovery.[10]

How Much Weight Should You Gain During Pregnancy?

The IOM 2009 guidelines are the universal standard for gestational weight gain, endorsed by RANZCOG, ACOG, WHO, and FIGO.[1, 2, 3] Your recommended range depends on your pre-pregnancy BMI.

Singleton pregnancies

BMI categoryBMI rangeTotal gain (kg)
Underweight< 18.512.5–18.0
Normal weight18.5–24.911.5–16.0
Overweight25.0–29.97.0–11.5
Obese≥ 30.05.0–9.0

Twin pregnancies (provisional)[1, 9]

BMI categoryTotal gain (kg)
Normal weight16.8–24.5
Overweight14.1–22.7
Obese11.3–19.1
UnderweightInsufficient data

In the first trimester (weeks 1 to 13), all BMI categories are expected to gain 0.5 to 2 kg total. Some women gain nothing or lose weight due to nausea, which is generally not a concern. From week 14 onward, gain is approximately linear at the weekly rates shown above.[1, 8] These are ranges, not precise targets. Week-to-week fluctuations are normal due to fluid retention, constipation, and meal timing.

Risks of Gaining Too Much or Too Little

A 2017 JAMA meta-analysis of 1.3 million pregnancies by Goldstein et al. quantified the risks associated with weight gain outside the IOM guidelines.[4]

OutcomeBelow guidelinesAbove guidelines
Small for gestational age↑ 53% higher risk↓ 34% lower risk
Large for gestational age↓ 41% lower risk↑ 85% higher risk
Macrosomia↓ 40% lower risk↑ 95% higher risk
Preterm birth↑ 70% higher risk↓ 23% lower risk
Caesarean deliveryNo significant change↑ 30% higher risk

Excessive gain also increases the risk of gestational diabetes, pre-eclampsia, postpartum weight retention (the strongest predictor of long-term maternal obesity), and complications in future pregnancies.[3, 4] Insufficient gain is associated with nutrient deficiencies, fatigue, difficulty establishing breastfeeding, and low birth weight.[4]

Pregnancy Weight Gain in Australia

Approximately 45 percent of Australian women giving birth are overweight or obese, with rates ranging from 42 percent in NSW to 52 percent in SA and Tasmania. Some rural areas report rates over 65 percent.[5, 3] Globally, only about 30 percent of women gain within IOM recommendations, with 47 percent gaining above and 23 percent gaining below the guidelines.[4]

Gestational diabetes: the rising complication

Almost 1 in 5 (18%) Australian women giving birth in hospital in 2021 to 2022 had gestational diabetes, a rate that has more than doubled since 2012 to 2013.[6, 7] Key drivers include rising maternal age, higher rates of maternal overweight and obesity, and changing population demographics. One in two women with gestational diabetes will develop type 2 diabetes later in life.[6]

Australia has one of the highest caesarean rates in the developed world at approximately 37 percent of births. Maternal obesity is a significant contributing factor, and excessive gestational weight gain independently increases caesarean risk by about 30 percent.[4]

Factors That Affect Pregnancy Weight Gain

  • Pre-pregnancy BMI. The single biggest determinant. Higher BMI means lower recommended gain.[1]
  • Number of babies. Twin pregnancies require significantly more weight gain.[1, 9]
  • Morning sickness. Severe nausea can cause weight loss in the first trimester, which is usually temporary and not harmful if it resolves by the second trimester.
  • Gestational diabetes. Women with GDM may be placed on dietary management that affects weight gain patterns.[6]
  • Pre-eclampsia. Can cause rapid weight gain from fluid retention, not fat. This is a medical concern, not dietary.
  • Activity level. RANZCOG recommends 30 to 45 minutes of brisk walking daily for most pregnant women.[3]
  • Previous pregnancies. Even 1 to 2 BMI units of inter-pregnancy weight gain increases risk of complications.[3]

Limitations of Pregnancy Weight Gain Calculators

  • Ranges, not targets. The IOM guidelines are population-level guidance, not individualised prescriptions.[1, 13]
  • No obesity sub-classification. A woman with a BMI of 31 and a woman with a BMI of 48 receive the same recommendation. There is active debate that lower gain may be appropriate for Class III obesity.[14]
  • Twin guidelines are provisional. Based on limited evidence, not the rigorous outcomes analysis used for singletons.[1, 9]
  • Daily fluctuations. Fluid retention, constipation, and time of day can cause day-to-day swings of 1 to 2 kg or more. Weekly weigh-ins are more reliable.[18]
  • Ethnic data limitations. These guidelines were developed primarily from North American and European data.[1]

Healthy Habits for Managing Weight During Pregnancy

  • Diet. Pregnancy is not eating for two. Energy needs only increase by approximately 340 kcal per day in the second trimester and 450 kcal in the third.[16] Focus on nutrient density: folate, iron, calcium, iodine, and omega-3. The Australian Dietary Guidelines recommend 5 serves of vegetables and 2 serves of fruit per day during pregnancy.[15]
  • Exercise. RANZCOG recommends 30 to 45 minutes of moderate exercise like brisk walking or swimming on most days. Exercise during pregnancy is safe for most women and associated with healthier weight gain, reduced GDM risk, and better mental health.[3]
  • Monitoring. Regular weigh-ins at each antenatal visit help track whether gain is within range. Sudden rapid weight gain of more than 1 kg in a week in the third trimester should be reported as it may indicate pre-eclampsia.[17]

References

  1. 1.Weight Gain During Pregnancy: Reexamining the Guidelines. Institute of Medicine (IOM), National Academies Press, 2009. www.nationalacademies.org/read/12584/chapter/2
  2. 2.Weight Gain During Pregnancy — Committee Opinion No. 548. American College of Obstetricians and Gynecologists (ACOG), 2013. www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/01/weight-gain-during-pregnancy
  3. 3.Management of Obesity in Pregnancy (C-Obs 49). Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). www.ranzcog.edu.au/wp-content/uploads/Management-Obesity-Pregnancy.pdf
  4. 4.Association of gestational weight gain with maternal and infant outcomes. Goldstein RF et al. JAMA, 2017; 317(21): 2207–2225. jamanetwork.com/journals/jama/fullarticle/2630599
  5. 5.Australia’s Mothers and Babies: Maternal Body Mass Index. Australian Institute of Health and Welfare (AIHW). www.aihw.gov.au/reports/mothers-babies/australias-mothers-babies/contents/antenatal-period/maternal-body-mass-index
  6. 6.Gestational diabetes. Australian Institute of Health and Welfare (AIHW). www.aihw.gov.au/reports/diabetes/diabetes/contents/how-common-is-diabetes/gestational-diabetes
  7. 7.Incidence of gestational diabetes in Australia: changing trends. Australian Institute of Health and Welfare (AIHW). www.aihw.gov.au/reports/diabetes/incidence-of-gestational-diabetes-in-australia/contents/changing-trends
  8. 8.New IOM guidelines: what OB/GYNs should know. Rasmussen KM, Yaktine AL. PMC, 2009. pmc.ncbi.nlm.nih.gov/articles/PMC2847829/
  9. 9.Weight gain in twin gestations. Fox NS et al. PMC, 2015. pmc.ncbi.nlm.nih.gov/articles/PMC4486049/
  10. 10.Composition of gestational weight gain. Hytten FE. NCBI Bookshelf, 1991. www.ncbi.nlm.nih.gov/books/NBK32815/
  11. 11.Managing your weight gain during pregnancy. MedlinePlus, U.S. National Library of Medicine. medlineplus.gov/ency/patientinstructions/000603.htm
  12. 12.Pregnancy weight gain: What’s healthy?. Mayo Clinic. www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy-weight-gain/art-20044360
  13. 13.Weight gain application of IOM guidelines. Gilmore LA et al. PMC, 2015. pmc.ncbi.nlm.nih.gov/articles/PMC4340812/
  14. 14.Obesity during pregnancy, birth and postpartum. Safer Care Victoria. www.safercare.vic.gov.au/best-practice-improvement/clinical-guidance/maternity/obesity-during-pregnancy-birth-and-postpartum
  15. 15.Healthy eating when you’re pregnant or breastfeeding. Eat for Health, NHMRC. www.eatforhealth.gov.au/eating-well/healthy-eating-throughout-all-life/healthy-eating-when-you%27re-pregnant-or-breastfeeding
  16. 16.Nutrient Reference Values for Australia and New Zealand. National Health and Medical Research Council (NHMRC). www.nhmrc.gov.au/sites/default/files/images/nutrient-refererence-dietary-intakes.pdf
  17. 17.Antenatal care — Chapter 2. Royal Australian College of General Practitioners (RACGP). www.racgp.org.au/clinical-resources/clinical-guidelines/key-racgp-guidelines/view-all-racgp-guidelines/national-guide/chapter-2-antenatal-care
  18. 18.Antenatal care addressing gestational weight gain (2024). PMC. pmc.ncbi.nlm.nih.gov/articles/PMC10845753/

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Frequently Asked Questions

Common questions about pregnancy weight gain, the IOM guidelines, and what to expect in Australia.

How much weight should I gain in the first trimester?

For all BMI categories, the IOM recommends a total of 0.5 to 2 kg during the first 13 weeks. Some women gain nothing or even lose weight due to morning sickness, and this is common and usually not a concern. If you lose more than 5 percent of your body weight due to severe vomiting (hyperemesis gravidarum), speak with your care provider. Significant weight gain should not happen yet because most pregnancy-specific growth occurs from the second trimester onward.

I'm overweight. Should I try to lose weight during pregnancy?

No. Weight loss during pregnancy is generally not recommended, even for women with obesity. The goal for overweight and obese women is limited, appropriate weight gain (7 to 11.5 kg for overweight, 5 to 9 kg for obese), not weight loss. RANZCOG and Safer Care Victoria emphasise limited weight gain rather than weight loss as the primary goal. For women with extreme obesity (BMI 50 or above), more restrictive gain may be considered under close medical supervision. The best time for weight loss is before conception or after pregnancy and breastfeeding.

Does the recommended weight gain change for twin pregnancies?

Yes. The IOM provides provisional guidelines for twins with higher weight gain targets: 16.8 to 24.5 kg for normal weight, 14.1 to 22.7 kg for overweight, and 11.3 to 19.1 kg for obese women. There is no guideline for underweight women carrying twins due to insufficient evidence. These twin guidelines are provisional and based on more limited evidence than the singleton recommendations. For triplets or higher-order multiples, no formal guidelines exist.

What if I'm gaining too fast or too slow?

If gaining faster than recommended, first rule out fluid retention. Sudden gain of more than 1 kg per week in the third trimester may indicate pre-eclampsia, not fat. Review your diet and activity level, and your care provider may refer you to a dietitian. Do not crash diet or severely restrict food. If gaining slower than recommended, persistent poor weight gain in the second and third trimesters warrants investigation. Your provider may order growth scans to monitor fetal development and refer you to an Accredited Practising Dietitian.

Do the guidelines change for different ages or ethnicities?

The IOM 2009 guidelines are explicitly designed to be independent of age, parity, ethnicity, race, and smoking status. However, some research suggests they may not be equally applicable to all populations as they were primarily derived from North American and European data. Some studies suggest Asian women may have higher risk at lower BMI thresholds. Older mothers face higher baseline risks for gestational diabetes and hypertension regardless of weight gain. Aboriginal and Torres Strait Islander women have higher rates of overweight, obesity, and gestational diabetes, and culturally appropriate support is important.

How is pregnancy weight gain different from regular weight gain?

Pregnancy weight gain is not all or even mostly fat. Only about 2.7 to 3.6 kg of the recommended gain is maternal fat stores. The rest includes the baby at approximately 3.4 kg, the placenta, amniotic fluid, extra blood volume, uterus growth, breast tissue, and extra body fluid. Much of this pregnancy-specific weight is lost within the first few weeks postpartum. Most women lose about 5 to 6 kg immediately after birth from the baby, placenta, and amniotic fluid. The remaining weight loss happens over the following weeks to months.

Is it normal to lose weight in early pregnancy?

Yes. Weight loss in the first trimester due to morning sickness, food aversions, or nausea is very common. About 70 to 80 percent of pregnant women experience some degree of nausea. A loss of 1 to 2 kg is generally not a concern. Hyperemesis gravidarum, which is severe persistent vomiting, affects about 1 to 3 percent of pregnancies and can cause significant weight loss requiring medical treatment. If you lose more than 5 percent of your pre-pregnancy body weight or cannot keep fluids down, contact your healthcare provider.

Does gestational diabetes affect how much weight I should gain?

The IOM weight gain guidelines technically apply regardless of gestational diabetes status. However, in practice, women with gestational diabetes are placed on managed diets that may result in different weight gain patterns. Gestational diabetes is associated with excessive fetal growth, so managing weight gain becomes particularly important. In Australia, almost 1 in 5 women giving birth in hospital have gestational diabetes. Screening typically occurs at 24 to 28 weeks via the oral glucose tolerance test. Women with gestational diabetes should follow their endocrinologist's or diabetes educator's specific dietary guidance.

How does pregnancy weight gain affect breastfeeding?

Maternal fat stores of 2.7 to 3.6 kg from the pregnancy gain serve as an energy reserve for breastfeeding. Breastfeeding increases energy expenditure by approximately 2,000 to 2,100 kJ per day (480 to 500 kcal). Women who gained within the IOM guidelines and breastfeed exclusively tend to return to pre-pregnancy weight more quickly. Excessive weight gain is the strongest predictor of long-term postpartum weight retention. Crash dieting while breastfeeding is not recommended as it can reduce milk supply and nutrient quality.

Should I weigh myself every day during pregnancy?

Daily weighing is generally not recommended because it can cause unnecessary anxiety due to normal daily fluctuations of 1 to 2 kg from water, food, sodium, and bowel movements. Weekly weigh-ins at the same time of day provide a more reliable picture. The Australian Clinical Practice Guidelines recommend weighing at the first and subsequent antenatal visits. Track trends over weeks, not individual readings. Some women find tracking weight triggering, especially those with a history of eating disorders. Report any sudden weight gain of more than 1 kg in a single week in the third trimester as it may indicate fluid retention or pre-eclampsia.