Pregnancy Weight Gain Calculator
Find the recommended pregnancy weight-gain range from your pre-pregnancy BMI, plus the expected gain by your current week, based on the Institute of Medicine guidelines.
Comment utiliser cette calculatrice
- 1Choose your units and enter your height and pre-pregnancy weight.
- 2Enter your current week of pregnancy.
- 3Optionally add your current weight to compare against the expected range.
- 4Read the recommended total gain for your pre-pregnancy BMI category.
Comment ça marche
Pregnancy weight gain (IOM)
pre-pregnancy BMI = weight ÷ height² (× 703 for lb/in) underweight (BMI<18.5): 28–40 lb total normal (18.5–24.9): 25–35 lb; overweight (25–29.9): 15–25 lb obese (≥30): 11–20 lb; ~1–4 lb in the first trimester
Recommended pregnancy weight gain depends on how much a person weighed before becoming pregnant, measured by pre-pregnancy body mass index. The reasoning is that someone starting underweight needs to gain more to support a healthy pregnancy, while someone starting with a higher BMI needs to gain less. The Institute of Medicine sets total gain ranges for each BMI category: the lower the starting BMI, the wider and higher the recommended range. Most of the gain comes in the second and third trimesters, with the first trimester typically adding only a few pounds. The recommendations translate into a rough weekly rate for the later trimesters, which is how progress is usually tracked. These are population guidelines for a single baby; the actual right amount for any individual is a matter for their care provider, and twins or other circumstances change the figures.
Exemple détaillé
A woman 65 inches tall who weighed 140 pounds before pregnancy has a BMI of about 23.3, in the normal range, so the recommended total gain is 25 to 35 pounds. By week 20 she'd be expected to have gained roughly 8 to 11 pounds, most of it in the second trimester at close to a pound a week.
Pregnancy Weight Gain Calculator : le guide complet
Why the recommendation depends on starting weight
There is no single healthy amount of weight to gain in pregnancy, because the right amount depends on where you start. The guidelines are built around pre-pregnancy body mass index for a clear reason: a person who begins pregnancy underweight has fewer reserves and benefits from gaining more, while a person who begins with excess weight can support a healthy pregnancy with a smaller gain. Tailoring the target to starting BMI aims to give the baby what it needs for healthy growth while managing risks for the mother.
The ranges reflect a balance of risks on both sides. Gaining too little is associated with a higher chance of a low-birthweight baby and preterm birth, while gaining too much raises the risk of a large baby, delivery complications, gestational diabetes, and weight that is hard to lose afterward. The recommended range for each category is the zone where these risks are lowest on average. Because it is a range rather than a single number, there is comfortable room for individual variation within it — the goal is to stay broadly on track, not to hit an exact figure.
How the gain unfolds across the trimesters
Pregnancy weight gain is not spread evenly; it accelerates as the pregnancy progresses. In the first trimester, when the embryo is tiny, most people gain very little — often just one to four pounds, and some gain nothing or even lose a little to morning sickness. This is entirely normal and no cause for concern. The bulk of the gain comes in the second and third trimesters, as the baby grows rapidly and the placenta, amniotic fluid, increased blood volume, and maternal tissue all add weight.
During those later trimesters, a fairly steady weekly rate is expected, and it is the main way progress is monitored. For someone of normal starting weight, that is roughly a pound a week; for those starting overweight or obese, somewhat less. This is why the calculator estimates an expected gain by your current week — comparing your actual gain to that trajectory is more informative than looking at the total alone, since it shows whether the rate is on track at this stage. Sudden large jumps or sustained gain well above the expected rate are worth mentioning to a care provider, as they can occasionally signal issues like fluid retention.
Guidelines, not targets
It is important to hold these numbers loosely. They are population-level guidelines derived from research on what tends to produce the healthiest outcomes across many pregnancies, not a personal prescription. Every pregnancy is different, and a care provider considers the whole picture — the mother's health, how the baby is growing, any complications, and individual circumstances — when advising on weight. The calculator's figures are a useful reference point for a conversation, not a substitute for that individualised care.
It also helps to remember what pregnancy weight gain actually is. It is not simply fat; it is the baby, the placenta, amniotic fluid, a larger uterus and breasts, extra blood and fluid, and some maternal fat stores that support breastfeeding. Healthy weight gain is a sign of a growing pregnancy, and the emphasis of modern guidance is on steady, appropriate gain through good nutrition rather than on restriction. Fixating on the scale can be counterproductive; the aim is nourishing the pregnancy well and staying broadly within a sensible range, with the numbers here as a gentle guide rather than a strict rule.
Questions fréquentes
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. The Institute of Medicine recommends 28–40 lb if underweight, 25–35 lb if normal weight, 15–25 lb if overweight, and 11–20 lb if obese, for a single baby. Most of the gain comes in the second and third trimesters.
How much should I have gained by now?
Very little in the first trimester — often just 1 to 4 pounds. After that, a fairly steady weekly rate: around a pound a week for normal-weight women, less if starting overweight. The calculator estimates the expected range for your current week so you can see if you're on track.
Is it bad to gain weight too fast or too slow in pregnancy?
Both carry risks. Too little gain is linked to low birthweight and preterm birth; too much to a large baby, delivery complications, and gestational diabetes. The recommended range minimises these risks. Sudden large jumps are worth mentioning to your care provider.
What does pregnancy weight gain consist of?
Not just fat. It includes the baby, placenta, amniotic fluid, an enlarged uterus and breasts, increased blood and fluid volume, and some maternal fat stores for breastfeeding. Healthy gain reflects a growing pregnancy, which is why steady, appropriate gain — not restriction — is the goal.