Pregnancy weight gain calculator

Enter the weight you had just before you became pregnant and your height, and the calculator shows a healthy range of weight gain for a pregnancy with one baby.

How to use the pregnancy weight gain calculator

The calculator needs two numbers. Choose kg and cm, or lb and feet with inches.

1. Weight before pregnancy. Use your weight just before you conceived. If you are not sure, the weight measured at your first antenatal appointment is a reasonable stand-in, as long as it was early in pregnancy.
2. Height. Your height without shoes.

Press Calculate. You see three results:

• Recommended total weight gain for the whole pregnancy.
• Your BMI before pregnancy, which decides the range.
• Weekly gain in the second and third trimester, from about week 14 until birth.

Your figures are not stored or sent anywhere. You can use the tool before pregnancy too, to understand what lies ahead.

How much weight should you gain in pregnancy?

The guideline sorts people into four groups by BMI before pregnancy. Each group has a total range for the whole pregnancy and a weekly range for the second half.

The weekly figures assume that you gain only a little, around 0.5 to 2 kg, in the first trimester. Many people gain less in those early weeks, often because of nausea, and that is usually nothing to worry about.

A worked example

Say you weighed 98 kg before pregnancy and are 1.65 m tall. Your BMI was 98 ÷ (1.65 × 1.65), which is about 36. That puts you in the group of 30 and above.

A healthy total gain would be 5 to 9 kg, so you might weigh roughly 103 to 107 kg at the end of pregnancy. From about week 14, a typical weekly gain would be 0.17 to 0.27 kg.

In practice, gain is not a straight line. Some weeks the scale barely moves, other weeks it jumps because of fluid. Your midwife looks at the overall pattern together with your baby’s growth.

Keeping an eye on your gain at home

You do not have to weigh yourself during pregnancy. Some people find it reassuring, others find it stressful, and both are fine. If you do want to keep track, a few simple rules make the numbers more meaningful.

• Weigh yourself no more than once a week, on the same day, at the same time, ideally in the morning after using the toilet.
• Use the same scale on a hard floor and wear similar clothing each time.
• Write the numbers down and look at the trend over a month, not at one week.
• If your gain is clearly above or below your range for several weeks, mention it at your next appointment rather than changing what you eat on your own.

A sudden jump of a kilo or more within a few days, especially with swelling of your face or hands or a headache, is different. That can be fluid linked to high blood pressure, so contact your midwife the same day.

Why is some weight gain needed at every BMI?

Pregnancy builds a whole support system around the baby, and all of it weighs something. That is why even someone who starts with a high BMI is advised to gain, not to stay the same or lose.

The gain is made up of:

• the baby;
• the placenta and the amniotic fluid around the baby;
• the growing womb and larger breasts;
• a large increase in blood volume, plus extra fluid in the tissues;
• some fat stores, which help provide energy for breastfeeding.

When the starting weight is higher, the body already has more energy reserves. So less extra fat is needed, and the recommended range is lower. The other parts of the gain, such as the baby, placenta and blood, are needed by everyone.

Where the numbers come from

The ranges come from a report by the Institute of Medicine and the National Research Council in the United States: Weight gain during pregnancy: reexamining the guidelines. A committee of experts reviewed the evidence on gain during pregnancy and the health of mothers and babies, and updated the earlier advice.

Two changes were important. The report switched to the World Health Organization’s BMI categories, and it set, for the first time, a specific and narrower range for people with obesity. The American College of Obstetricians and Gynecologists has endorsed and reaffirmed the ranges.

How the calculator works:

1. It calculates your BMI before pregnancy: weight in kg divided by height in metres squared.
2. It places you in one of the four groups in the table above.
3. It shows the total and weekly range for that group, converted to pounds if you chose lb.

What the evidence shows

A large analysis in JAMA pooled data on more than a million pregnancies. Nearly half gained more than the guideline and around a quarter gained less.

Gaining more than the range was linked to a larger chance of a big baby and a caesarean section. Gaining less was linked to a higher chance of a small baby and preterm birth. Both directions carried some risk, which is why the advice is a range rather than “as little as possible”.

Pregnancy weight gain when you live with obesity

If your BMI was 30 or more before pregnancy, the guideline suggests one range, 5 to 9 kg, regardless of whether your BMI was 31 or 45. The expert committee did not set separate ranges for higher classes of obesity because there was not yet enough good evidence.

Researchers have continued to study this group. Some studies suggest that a gain below 5 kg can go well for some people with a very high BMI, but the evidence is mixed and it does not make weight loss a goal.

No current guideline advises losing weight during pregnancy. If you gain less than expected, your care team will check your baby’s growth and your diet rather than tell you to eat more for the sake of the number.

You deserve the same respect and care as anyone else. In some countries you will not be weighed at every visit; in others you will. You can always ask what your weight is being used for and say how you would prefer to hear about it.

For a broader look at pregnancy with a higher weight, including fertility, extra checks and planning ahead, read our page on obesity and pregnancy.

Is it safe to diet during pregnancy?

Pregnancy is not the time to cut calories or follow a weight-loss plan, even if your BMI is high. Your baby depends on a steady supply of energy, protein, iron, folate, iodine and other nutrients that come from your meals.

Very low-calorie or fasting diets, skipping meals, cutting out whole food groups and “detox” products can all leave you and your baby short of what you need. Medicines for weight loss are not used during pregnancy at all; if you used one before, follow your doctor’s advice.

What does help is eating well, not eating less. In practical terms:

• Build meals around vegetables, fruit, wholegrains, pulses, dairy or calcium-fortified alternatives, and protein such as eggs, fish, beans or lean meat.
• Choose water, milk or unsweetened tea instead of sugary drinks.
• Eat regular meals and keep healthy snacks at hand, which also helps with nausea.
• Take the supplements your midwife or doctor recommends, such as folic acid in early pregnancy.

“Eating for two” is a myth

You do not need to double your food. In the first three months, energy needs hardly change. Later in pregnancy they rise moderately: the European Food Safety Authority estimates about 260 extra kcal a day in the second trimester and about 500 in the third, for someone with a healthy weight gain.

That is the size of a sandwich or a bowl of yoghurt with fruit and nuts, not a second dinner.

A Cochrane review of trials found that advice on diet, exercise or both lowered the chance of gaining more than recommended by about a fifth. Small, steady habits work.

Staying active during pregnancy

For most people with an uncomplicated pregnancy, regular movement is safe and good for both mother and baby. This is true for people living with obesity too.

The Canadian guideline on physical activity in pregnancy and the American College of Obstetricians and Gynecologists both recommend building up to about 150 minutes of moderate activity a week, spread over at least three days, and ideally a little every day. Moderate means you can talk but not sing.

If you were not active before pregnancy, start with 10 to 15 minutes and add a few minutes at a time. Walking is ideal; our walking guide explains how to begin with only a few minutes. Seated and supported exercises from Level Start in our free workouts can be a gentle option, but check with your midwife first and skip anything that feels uncomfortable.

Stop exercising and contact your midwife or doctor if you have vaginal bleeding, fluid leaking, regular painful contractions, chest pain, dizziness or feeling faint, a severe headache, calf pain or swelling, or breathlessness before you start moving.

Limits: who should be careful

The calculator gives general ranges for adults expecting one baby. It does not replace the advice of your midwife, obstetrician or doctor, who may set a different target for you.

• Twins or more: the ranges are higher; the calculator does not cover them.
• Teenage pregnancy: young mothers are still growing, so adult BMI groups may not fit. Ask your care team.
• Gestational diabetes or diabetes from before pregnancy: your team may give specific food and weight advice; follow it.
• High blood pressure or pre-eclampsia: sudden weight gain or swelling can be a warning sign. Contact your midwife if your face, hands or feet swell quickly.
• A history of eating disorders: pregnancy can bring old worries back. Tell your midwife, and consider skipping the numbers and asking not to be told your weight. Our page on psychological support explains where to find help.
• Severe sickness (hyperemesis): if you cannot keep food or drinks down, contact your doctor; weight targets come second.
• Asian heritage: the calculator uses the standard BMI groups from the guideline. Some countries use lower cut-offs for Asian populations; ask locally which applies.

What to do next

Use your range as a starting point for a conversation, not as a pass or fail test. Bring it to your next appointment and ask how it fits your situation.

If you are planning a pregnancy

The months before pregnancy are a good time to build habits that last: regular meals, more vegetables and pulses, fewer sugary drinks and daily walks. Even modest weight loss before conception can improve health, as our page on pregnancy with a higher weight describes. A free personal eating plan can help you get there step by step.

If you are pregnant now

• Follow your midwife’s or doctor’s advice on weight, food and activity first.
• Eat regular, varied meals; our eating plan gives ideas you can adapt to pregnancy, leaving out foods your care team advises against.
• Walk a little most days, if your midwife agrees.
• Talk to someone if you feel worried about your weight. You can book a free video meeting (in English) with our team.

After the birth

Weight usually comes down gradually in the months after birth, and breastfeeding can help a little. Give yourself time to recover before you think about weight loss, and start with gentle walks. In the free Obesity Foundation Club you can find encouragement for this next stage.

Related calculators

• BMI calculator: check your BMI before or after pregnancy.
• Water intake calculator: everyday drinking needs (pregnancy adds a little more).
• Heart rate zones calculator: background on exercise intensity; in pregnancy, rely on the talk test.