Pregnancy weight gain calculator
Enter your height, your weight before pregnancy and your week. You will see a recommended range for the whole pregnancy and for today, with a chart of where you stand. Your numbers stay in your browser.
About you
Guideline options
Your numbers stay in your browser. We never receive them.
Enter your height and weight to see your range
Example: 165 cm and 60 kg gives a BMI of 22.0, in the healthy weight group, so 11.5 to 16 kg (25 to 35 lb) over the whole pregnancy with one baby. Your own numbers replace this as soon as you type them.
Recommended gain by week
Example: healthy-weight BMI, one baby, IOM ranges.
Recommended rangeYour gain so far
See the week-by-week table
| Week | Recommended gain so far |
|---|
More pregnancy calculators
See all pregnancy calculatorsHow the calculator works
- 1Work out your BMI Weight (kg) ÷ height (m)² Your height and your weight before pregnancy give your body mass index. If you do not know your weight before pregnancy, use your first weight in early pregnancy.
- 2Find your group Under 18.5, 18.5 to 24.9, 25 to 29.9, 30 or more The group sets the range for your whole pregnancy. The Asian cut-off option starts the groups at 23 and 27.5, and the China option uses 24 and 28.
- 3Place today in the range First trimester allowance, then a steady rate The guideline allows 0.5 to 2 kg by week 13 and a weekly rate after that. The calculator draws a band between them and shows where your gain so far sits.
What this range can and cannot tell you
A range is a guide drawn from large groups of people. It starts a conversation with your care team and does not grade you.
What the calculator uses
- Your height and your weight before pregnancy.
- Whether you are expecting one baby or twins, and your week of pregnancy.
- If you add it, your current weight, to compare with the range for your week.
- The guideline you choose: IOM 2009, IOM with Asian BMI cut-offs, or the 2022 Chinese standard.
What it cannot tell you
- Say whether your pregnancy is healthy. Weight is one of many signs, and many healthy pregnancies fall outside a range.
- Account for swelling, a starting weight measured long ago, or conditions such as gestational diabetes or severe nausea. Your care team can.
- Set a target for you. The NHS does not set one at all.
- Give a range for twins when you start underweight, because the source has none.
- Replace your clinic’s advice, which comes first.
Recommended weight gain by BMI
Most calculators, this one by default, use ranges from a 2009 review by the US Institute of Medicine, now the National Academy of Medicine. It set a range of total gain for each BMI group, a small allowance for the first trimester and a steady weekly rate after that. Health Canada's pregnancy weight gain calculator uses the same ranges.
| BMI group | BMI before pregnancy | Total gain, one baby | Weekly gain after week 13 | Twins (provisional) |
|---|---|---|---|---|
| Underweight | under 18.5 | 12.5 to 18 kg (28 to 40 lb) | 0.44 to 0.58 kg (1 to 1.3 lb) | No range set |
| Healthy weight | 18.5 to 24.9 | 11.5 to 16 kg (25 to 35 lb) | 0.35 to 0.50 kg (0.8 to 1 lb) | 17 to 25 kg (37 to 54 lb) |
| Overweight | 25 to 29.9 | 7 to 11.5 kg (15 to 25 lb) | 0.23 to 0.33 kg (0.5 to 0.7 lb) | 14 to 23 kg (31 to 50 lb) |
| Obesity | 30 or more | 5 to 9 kg (11 to 20 lb) | 0.17 to 0.27 kg (0.4 to 0.6 lb) | 11 to 19 kg (25 to 42 lb) |
The first trimester allowance is 0.5 to 2 kg (1.1 to 4.4 lb) in total. The twin ranges are provisional, and the Academies gave no range for twins when a pregnancy starts underweight because there was too little data.
How guidance differs around the world
The IOM ranges come from a US review, and not every country follows them. The table shows three published sets for one baby, for the same four BMI groups. Cut-offs differ a little: China uses 24 and 28 for overweight and obesity, and the others use 25 and 30.
| BMI group | IOM 2009 (US, Canada) | China 2022 | Japan 2021 |
|---|---|---|---|
| Underweight | 12.5 to 18 kg | 11 to 16 kg | 12 to 15 kg |
| Healthy weight | 11.5 to 16 kg | 8 to 14 kg | 10 to 13 kg |
| Overweight | 7 to 11.5 kg | 7 to 11 kg | 7 to 10 kg |
| Obesity | 5 to 9 kg | 5 to 9 kg | Individual advice, up to about 5 kg |
United Kingdom. The NHS says most people gain between 10 kg and 12.5 kg (22 to 28 lb), mostly after week 20, and sets no target. It advises against dieting in pregnancy and says that some naturally slim women stay slim and have healthy babies. People with a BMI over 30 or under 18.5 may get special advice.
China. A 2022 national standard (WS/T 801-2022) set ranges for Chinese women using Chinese BMI cut-offs, with 0 to 2 kg allowed in the first trimester. It covers one baby and does not apply below 140 cm in height or above 125 kg before pregnancy.
Japan. The Japan Society of Obstetrics and Gynecology revised its ranges in 2021 and raised them, and the health ministry adopted the new advice.
Asian BMI cut-offs. In 2004 a WHO expert consultation found that health risks rise at lower BMIs in many Asian populations. It described extra action points at BMI 23 and 27.5 and left each country to set its own definitions. Some hospitals, such as the Royal Women's Hospital in Melbourne, publish tables that use the lower cut-offs. The calculator's Asian option applies the same cut-offs to the IOM ranges. That is an adaptation and not an IOM recommendation, so ask your care team which approach they use.
Weight gain by trimester
First trimester, weeks 1 to 13. Gain is small. The guideline allows 0.5 to 2 kg in total, and many people gain nothing, or lose a little while nausea is strong. If you cannot keep food down, call your care team. Small, regular meals often help, and our guide to easing nausea with food has ideas.
Second trimester, weeks 14 to 27. Appetite returns for many people and gain becomes steadier. The weekly rate in the table above applies from week 14. Our week 14 guide covers eating and weight in the second trimester.
Third trimester, weeks 28 to 40. The baby grows fastest and the weekly rate stays about the same. The NHS says most weight is gained after week 20.
Where the weight goes
Only part of the gain is body fat. A baby at term averages about 3.4 kg (7.5 lb). The placenta, the amniotic fluid, a larger uterus and breasts, extra blood and body fluid make up much of the rest, and the body keeps some fat stores too. That is why swelling and fluid count toward the total and why the number on the scale can jump from day to day.
Weight gain describes your own body and says little about your baby's size. Your care team measures the baby's growth at scans and with fundal height checks, and our week-by-week guide shows how your baby grows.
What gaining more or less can mean
A 2017 review in JAMA pooled 23 studies of 1,309,136 women and compared outcomes with the IOM ranges. Among women who gained less than the range, small babies for their gestational age were 1.53 times as likely (as an odds ratio) and preterm birth was 1.70 times as likely. Among women who gained more, large babies for their gestational age were 1.85 times as likely, very large babies (macrosomia) were 1.95 times as likely and a caesarean birth was 1.30 times as likely. In these studies 47% of pregnancies ended above the range and 23% below it.
These figures compare groups of people. They do not predict what will happen in your pregnancy, and many people outside a range have healthy babies. They are the reason clinicians watch weight gain, and they are not a reason to restrict food. If you gain faster or slower than the range, tell your care team and ask what fits you.
Tracking without stress
- Weighing is optional. The total range does not need your current weight, so leave that box empty if watching the scale feels stressful.
- Tell your care team about your history. If you have had an eating disorder, or if weighing is hard for you, say so. They can support you and adjust how weight is discussed.
- Eat regularly. Pregnancy is not a time to diet. Our guides to the best foods and the foods to avoid cover what to put on your plate.
- Move in ways that feel good. Gentle movement such as walking is usually fine. Ask your care team before beginning anything strenuous.
- Know the warning signs. Call your care team about a sudden gain with swelling in the face or hands, a severe headache or changes in vision.
If you have just had a positive test and want to date your pregnancy, the due date calculator does it from your last period, and the hCG calculator checks a blood test result.
Common questions
Short answers about ranges, weekly gain and what to do when you are outside them.
How does a weight gain while pregnant calculator work?
It works out your body mass index from your height and your weight before pregnancy, finds the recommended range for that group and draws a band for each week. Enter your week and current weight and it shows whether your gain so far sits inside the band. The range comes from the guideline you pick, and the result is a guide for a conversation with your care team.
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. For one baby, the 2009 IOM ranges are 12.5 to 18 kg (28 to 40 lb) if you start underweight, 11.5 to 16 kg (25 to 35 lb) at a healthy weight, 7 to 11.5 kg (15 to 25 lb) if overweight and 5 to 9 kg (11 to 20 lb) with obesity. The NHS says most people gain between 10 kg and 12.5 kg and sets no target.
How much weight should I gain each week?
In the first trimester the guideline allows 0.5 to 2 kg in total. From week 14 the weekly rate is about 0.44 to 0.58 kg if you start underweight, 0.35 to 0.50 kg at a healthy weight, 0.23 to 0.33 kg if overweight and 0.17 to 0.27 kg with obesity. Gain does not have to be even from week to week.
How much weight should I gain with twins?
The National Academies give provisional ranges of 17 to 25 kg (37 to 54 lb) for a healthy starting weight, 14 to 23 kg (31 to 50 lb) if overweight and 11 to 19 kg (25 to 42 lb) with obesity. They give no range when you start underweight because there was too little data. Your care team sets a plan with you.
Is it normal not to gain weight in the first trimester?
Yes. Many people gain little or nothing, and strong nausea can mean a small loss. The guideline allows 0.5 to 2 kg by week 13. If you cannot keep food down, call your care team. Our guide to easing nausea with food has practical ideas.
What if I am gaining faster or slower than the range?
A range describes groups of people and does not judge you. Tell your care team, who can look at the whole picture, including your baby’s growth. Research links gaining below the ranges with a higher chance of a smaller baby and preterm birth, and gaining above them with a higher chance of a larger baby and a caesarean birth. Those figures compare groups and do not predict what will happen to you.
What if I do not know my weight before pregnancy?
Use your weight from your first appointment in early pregnancy as a stand-in, and tell your midwife or doctor that you are using it. A weight from a few months ago is also fine if you have not changed much.
Should I try to lose weight if I start pregnancy above the healthy range?
Pregnancy is not a time to diet, according to the NHS. The IOM range for obesity is a gain of 5 to 9 kg, which is lower than the other groups. Ask your care team for advice that fits you.
Do I need to eat for two?
No. Quality matters more than quantity. The NHS says you do not need extra calories until about week 28. Our guide to the best foods in pregnancy lists nutrient-dense choices.
Which BMI cut-offs should I use if I am of Asian background?
In 2004 a WHO expert consultation described extra public health action points at BMI 23 and 27.5 for Asian populations and left each country to set its own definitions. The calculator offers an option that applies those cut-offs to the IOM ranges. It is an adaptation and not an IOM recommendation, so ask your care team which approach they use. China publishes its own national standard, which you can also choose.
Do other countries use different ranges?
Yes. China set a national standard in 2022 with ranges such as 8 to 14 kg for a healthy starting weight. Japan revised its ranges in 2021 and now uses 10 to 13 kg for the same group. The UK sets no range. These differences are why the page lets you choose a guideline.
Does swelling count as weight gain?
Yes, extra body fluid is part of normal gain. Call your care team if you notice a sudden gain with swelling in your face or hands, a severe headache or changes in your vision.
How accurate is this calculator?
It applies published ranges. For weeks between the first trimester and the end of pregnancy it draws a straight band between the guideline’s first trimester allowance and its total range, so weekly figures are estimates. Treat it as a guide for a conversation with your care team.
Does this tool save my weight?
No. The numbers stay in your browser and are never sent to us. A session store in your own tab keeps them until you close the tab.
Keep reading
Pregnancy diet 7 min read Easing nausea with food Small meals, ginger and bland snacks that help in the first trimester. 
Fertility foods 8 min read Best foods to eat when trying to conceive Leafy greens, beans, eggs and more, plus a simple one-day meal plan. 
Foods to avoid 9 min read Foods to avoid while pregnant High-mercury fish, raw foods, soft cheeses and why each one matters. Sources: National Academies: Weight Gain During Pregnancy, Reexamining the Guidelines (2009); China National Health Commission: Standard of Recommendation for Weight Gain during Pregnancy Period, WS/T 801-2022; Japan Society of Obstetrics and Gynecology 2021 ranges, as reported in BMC Pregnancy and Childbirth (2025); NHS: Weight gain in pregnancy; Health Canada: Pregnancy weight gain calculator; WHO expert consultation, 2004: Appropriate body-mass index for Asian populations (Lancet); Goldstein et al., 2017: Association of gestational weight gain with maternal and infant outcomes (JAMA); The Royal Women’s Hospital, Melbourne: Weight and pregnancy