Pregnancy Weight Gain Calculator
Healthy weight gain by week of pregnancy.
Your BMI category is based on your weight before you were pregnant, not your current weight.
Completed weeks, from 0 to 42.
Recommended total weight gain
11.5 to 16 kg
For a pre-pregnancy BMI of 23.0 (healthy weight) over the whole pregnancy.
At week 24, the recommended gain so far is 4.4 to 7.5 kg.
After the first trimester, about 0.42 kg a week is the average recommended rate for this BMI category (range 0.35 kg to 0.5 kg).
Recommended weight gain by week
- Recommended range
- Your gain so far
- Week 24
How to Use the Pregnancy Weight Gain Calculator
Enter your weight before pregnancy, your height and the current week of your pregnancy, and the calculator shows your pre-pregnancy BMI, the recommended total weight gain for your category, and the range you would typically expect to have gained by now. Add your current weight to see whether your gain so far is below, within or above that range, and choose twins if you are expecting more than one baby.
This is a pregnancy BMI calculator and a weight calculator in one: it uses your pre-pregnancy BMI to choose the right guideline, then shows a chart and a week-by-week table. Everything can be entered in kilograms and centimetres, or in pounds, feet and inches.
How the Recommended Range Is Worked Out
Weeks 0 to 13: recommended gain rises evenly from 0 to 0.5–2 kg
After week 13: 0.5 kg + (week − 13) × weekly rate (low), and 2 kg + (week − 13) × weekly rate (high), never above the total range
The categories use the BMI rounded to one decimal place, so a BMI of 24.96 is shown and treated as 25.0.
Recommended Weight Gain by Pre-Pregnancy BMI (Institute of Medicine, 2009)
These Institute of Medicine guidelines are widely used in Australian antenatal care, although your care provider may use slightly different targets.
| Pre-pregnancy BMI | Total gain (one baby) | Weekly rate after week 13 | Total gain (twins) |
|---|---|---|---|
| Underweight (Under 18.5) | 12.5 to 18 kg | 0.51 kg (0.44 to 0.58) | No guideline |
| Healthy weight (18.5 to 24.9) | 11.5 to 16 kg | 0.42 kg (0.35 to 0.5) | 17 to 25 kg |
| Overweight (25 to 29.9) | 7 to 11.5 kg | 0.28 kg (0.23 to 0.33) | 14 to 23 kg |
| Obese (30 or more) | 5 to 9 kg | 0.22 kg (0.17 to 0.27) | 11 to 19 kg |
Worked Example: 65 kg, 168 cm, Week 24
Suppose you weighed 65 kg before pregnancy, you are 168 cm tall, you are in week 24 with a single baby, and you now weigh 72 kg. Your pre-pregnancy BMI is 23.0, which is the healthy weight category, so the recommended total gain is 11.5 to 16 kg. At week 24 the recommended gain so far is 4.4 to 7.5 kg: 0.5 kg + 11 weeks × 0.35 kg for the low end, and 2 kg + 11 weeks × 0.50 kg for the high end. You have gained 7 kg, which is within the range.
The same pregnancy would look like this at other weeks: by week 13 the recommended range is 0.5 to 2 kg, by week 28 it is 5.8 to 9.5 kg, and by week 40 it is 10 to 15.5 kg. For comparison, with twins and the same BMI the recommended total would be 17 to 25 kg, or 10.2 to 15 kg by week 24.
Where the Weight Goes
Pregnancy weight is not all baby. It includes the placenta, amniotic fluid, the growing uterus and breasts, extra blood and body fluid, and some fat stores that help support pregnancy and breastfeeding. Gain also isn't steady: it is usually slower in the first trimester and faster in the second and third. Fluid shifts, a big meal or the time of day can move the scales by a kilogram or more, so look at the trend over several weeks rather than any single reading.
Talk to Your Midwife or Doctor
Guidelines describe averages, and your own pregnancy may have good reasons to sit outside them, for example morning sickness, a medical condition, or a multiple pregnancy. Please don't try to lose weight while pregnant unless your midwife, GP or obstetrician has advised it. If you are worried about gaining too much or too little, or about your eating, raise it at your next appointment, and ask about seeing an accredited practising dietitian if you would like nutrition support.
Frequently Asked Questions
- How much weight should I gain during pregnancy?
- It depends on your pre-pregnancy BMI. For a single baby, the Institute of Medicine guidelines recommend about 12.5 to 18 kg if you were underweight, 11.5 to 16 kg for a healthy weight, 7 to 11.5 kg if overweight and 5 to 9 kg if your BMI was 30 or more. Your midwife, GP or obstetrician may suggest a different range for your situation.
- How does a pregnancy weight gain calculator work?
- It works out your BMI from your weight before pregnancy and your height, picks the matching category, and then applies the guideline: about 0.5 to 2 kg over the first 13 weeks, followed by a steady weekly rate range for the rest of the pregnancy. It then shows the recommended range for your current week and, if you enter your current weight, whether your gain so far is below, within or above it.
- Is this a pregnancy BMI calculator? Which weight should I use?
- It calculates your BMI, but from your weight before you were pregnant, not your current weight, because the guidelines are based on where you started. Using your pregnant weight would overstate your BMI and could place you in the wrong category. If you don't know your pre-pregnancy weight, use your weight from early in the first trimester or the earliest measurement you have, and check with your midwife.
- Why does the recommended weight gain depend on BMI?
- Someone who starts pregnancy at a lower BMI generally needs to gain more to support the baby, the placenta and their own body, while someone who starts at a higher BMI generally needs to gain less. Gaining much more or much less than the typical range is linked with higher chances of some pregnancy and birth complications. That is why the guidelines are given in ranges for each BMI category.
- How much weight should I gain each week of pregnancy?
- In the second and third trimesters the average recommended rate is about 0.51 kg a week for an underweight BMI, 0.42 kg for a healthy weight, 0.28 kg for overweight and 0.22 kg for a BMI of 30 or more. Weight gain is rarely perfectly steady, so a single week above or below isn't a concern on its own. The week-by-week table shows the recommended range at every second week.
- What if I've gained more or less than the range?
- The ranges are guides based on large groups of pregnancies, and plenty of healthy pregnancies fall outside them. If you are above or below your range, or your weight is changing quickly, mention it at your next antenatal visit so your midwife or doctor can look at the whole picture. If you are struggling to gain weight, for example because of nausea, they can suggest ways to get enough nutrition.
- How much weight gain is recommended with twins?
- The Institute of Medicine's provisional guidelines for twins give total ranges of about 17 to 25 kg for a healthy pre-pregnancy BMI, 14 to 23 kg for overweight and 11 to 19 kg for a BMI of 30 or more. There is no standard guideline for twins when the BMI is under 18.5. Twin pregnancies are individual and often shorter, so your care team will usually guide you more closely.
- Where does the weight go during pregnancy?
- Only part of the extra weight is the baby. The rest is the placenta, amniotic fluid, a larger uterus and breasts, extra blood and body fluid, and some stored fat that supports pregnancy and breastfeeding. Because so much of it isn't fat, the number on the scales isn't a measure of how your body is coping, and this is another reason to avoid judging yourself by it.
- Can I diet or try to lose weight while I'm pregnant?
- Dieting to lose weight is generally not recommended during pregnancy unless a doctor or midwife advises it for a specific reason. Eating a varied, nourishing diet and staying active in ways your care provider is comfortable with is the usual approach. If you are worried about your weight, a GP, midwife or an accredited practising dietitian can help you with a plan that is safe for you and your baby.