Calculate recommended total and trimester-by-trimester weight gain during pregnancy based on your pre-pregnancy BMI and RANZCOG guidelines.
Recommended pregnancy weight gain depends on your pre-pregnancy BMI. General guidelines suggest 12.5–18 kg if you were underweight, 11.5–16 kg at a healthy weight, 7–11.5 kg if overweight, and 5–9 kg with obesity. Twin pregnancies need more. These are ranges to guide you, not exact targets — your provider personalises them.
| Trimester | Recommended gain |
|---|
The calculator first works out your pre-pregnancy BMI, then applies the matching range.
Weight gain is not evenly spread. Little is gained early; the steadiest gain is later.
| Trimester | Typical Gain | Notes |
|---|---|---|
| First (weeks 1–12) | 0.5–2 kg total | Often little; nausea can even cause loss |
| Second (weeks 13–26) | ~0.4 kg per week | Steady gain as baby grows |
| Third (weeks 27–40) | ~0.4 kg per week | Continued steady gain; may slow near the end |
Carrying twins requires more weight gain to support two babies. General guideline ranges are higher:
| Pre-Pregnancy BMI | Recommended Gain (Twins) |
|---|---|
| Healthy weight | 16.8–24.5 kg (37–54 lb) |
| Overweight | 14.1–22.7 kg (31–50 lb) |
| Obesity | 11.3–19.1 kg (25–42 lb) |
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) recommends weight gain based on pre-pregnancy BMI:
| Pre-pregnancy BMI | Singleton | Twins |
|---|---|---|
| Underweight (<18.5) | 12.5–18 kg | 17–25 kg |
| Normal (18.5–24.9) | 11.5–16 kg | 17–25 kg |
| Overweight (25–29.9) | 7–11.5 kg | 14–23 kg |
| Obese (≥30) | 5–9 kg | 11–19 kg |
The Institute of Medicine (IOM) 2009 guidelines — adopted by Australian midwifery and obstetric practice — set recommended gestational weight gain ranges based on pre-pregnancy BMI. The same guidelines are referenced by the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG).
| Pre-pregnancy BMI | Category | Total Weight Gain | Rate 2nd-3rd Trimester |
|---|---|---|---|
| Under 18.5 | Underweight | 12.5–18 kg | 0.5 kg/week |
| 18.5–24.9 | Normal weight | 11.5–16 kg | 0.4 kg/week |
| 25.0–29.9 | Overweight | 7–11.5 kg | 0.3 kg/week |
| 30.0+ | Obese | 5–9 kg | 0.2 kg/week |
| Twin pregnancy | Normal BMI | 17–25 kg | Varies |
| Component | Approximate Weight |
|---|---|
| Baby | 3.0–3.5 kg |
| Placenta | 0.5–0.7 kg |
| Amniotic fluid | 0.8–1.0 kg |
| Uterus enlargement | 0.8–1.0 kg |
| Breast tissue increase | 0.5–1.0 kg |
| Blood volume increase | 1.2–1.8 kg |
| Fat stores (maternal energy reserves) | 2.0–4.0 kg |
| Total typical gain | 9.0–12.0 kg for normal BMI |
Supporting healthy weight gain is about nourishing food and gentle movement, not restriction. A balanced approach helps both you and your baby.
| Focus | Practical Tips |
|---|---|
| Protein | Lean meat, eggs, legumes, dairy — supports baby's growth |
| Whole grains & fibre | Wholemeal bread, oats, brown rice — steady energy, aids digestion |
| Fruit & vegetables | Aim for variety and colour; a key source of vitamins |
| Key nutrients | Folate, iron, calcium and iodine are especially important |
| Hydration | Drink water regularly through the day |
| Food safety | Avoid high-mercury fish, unpasteurised dairy and undercooked meat |
Safe activity — such as walking, swimming, prenatal yoga and pelvic floor exercises — supports healthy weight gain and wellbeing for most pregnancies. Always check with your provider before starting or continuing exercise, as recommendations should be individualised.
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI: underweight (BMI under 18.5): 12.5-18 kg; normal weight: 11.5-16 kg; overweight: 7-11.5 kg; obese: 5-9 kg. These IOM 2009 guidelines are used by Australian midwives and obstetricians. Gaining within the recommended range reduces risks of complications for both mother and baby.
Is it normal to lose weight in the first trimester of pregnancy?
Weight loss or minimal gain (1-2 kg) in the first trimester is normal and common due to morning sickness and nausea. Most of the recommended weight gain occurs in the second and third trimesters. If you are losing significant weight in the first trimester due to severe nausea (hyperemesis gravidarum), discuss with your midwife or doctor.
What if I gain too much weight during pregnancy?
Excessive gestational weight gain is associated with: gestational diabetes, larger baby (increasing C-section risk), hypertension, and greater difficulty losing weight after pregnancy. However, calorie restriction during pregnancy is not recommended. Focus on nutrient-dense foods and regular moderate activity (as advised by your care team) rather than weight restriction.
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. General guidelines suggest 12.5–18 kg if underweight, 11.5–16 kg at a healthy weight, 7–11.5 kg if overweight, and 5–9 kg with obesity, for a single baby. These are ranges to guide you; your provider gives personalised advice during prenatal care.
How much weight should I gain in the first trimester?
Usually very little — often just 0.5 to 2 kg in total across the first 12 weeks. Some women gain nothing or even lose a little due to morning sickness, which is normal. Most pregnancy weight gain happens later, in the second and third trimesters.
How is pregnancy weight gain calculated?
The calculator first works out your pre-pregnancy BMI from your height and weight, then applies the recommended gain range for that BMI category. It can also show the expected gain for your current week. Enter your details above to see your personalised range.
How much weight should I gain with twins?
Twin pregnancies need more weight gain to support two babies. For a healthy pre-pregnancy BMI, guidelines suggest roughly 16.8–24.5 kg. Ranges are lower for higher BMI categories. Because multiple pregnancies vary so much, your maternity team will give individual guidance.
Is it safe to gain too little weight during pregnancy?
Gaining too little can be associated with a higher chance of a smaller baby or early birth. If you are gaining less than expected, or losing weight beyond early pregnancy, mention it to your doctor or midwife. They can check that you and your baby are getting enough nutrition.
Should I really eat for two during pregnancy?
No — "eating for two" is a myth. Most women need no extra calories in the first trimester and only around 340–450 extra calories per day in the second and third trimesters. Quality matters more than quantity: focus on nutritious foods rather than simply eating more.
When should I talk to my doctor about pregnancy weight?
Speak with your provider if you gain weight very rapidly, gain very little, or have sudden swelling with headache or vision changes, which can signal complications. Also raise any questions about nutrition, gestational diabetes or blood pressure. Regular prenatal visits are the best place to track healthy weight gain.