Pregnancy Weight Gain Calculator
Check your pregnancy weight gain against the Institute of Medicine guideline for your starting BMI.
Your pregnancy
Weight gain in pregnancy is monitored by your midwife or obstetrician alongside blood pressure, growth scans and everything else. A single week outside the band means very little; a consistent trend is worth raising. Never diet during pregnancy without medical supervision.
This gives a recommended total weight gain range for pregnancy, based on pre-pregnancy BMI.
It follows the Institute of Medicine guidelines and shows expected gain by trimester.
Recommended weight gain in pregnancy
Recommended weight gain in pregnancy depends on pre-pregnancy BMI, not on a single universal figure. That is the part most people do not realise.
The Institute of Medicine ranges are 28-40 lb if you started underweight, 25-35 lb at a normal BMI, 15-25 lb if overweight, and 11-20 lb if obese. Someone starting at a BMI of 32 has a recommended range less than half that of someone starting at 17.
The other correction worth making early: "eating for two" is quantitatively wrong. The additional energy requirement is roughly 340 extra calories a day in the second trimester and 450 in the third, and none at all in the first. That is a sandwich, not a second dinner.
Ranges are for a single baby. Twin pregnancies have their own, higher, recommendations.
What to enter
- Pre-pregnancy height and weight
- These give the BMI that determines your range. Pre-pregnancy weight, not current.
- Current week of pregnancy
- Gain is not spread evenly. Most of it happens in the second and third trimesters.
- Single or multiple pregnancy
- Twin pregnancies have separate, higher recommendations.
How the gain is distributed
- First trimester
- Only 1-4 lb in total. No additional calories are needed at this stage.
- Second trimester
- About 1 lb a week at a normal starting BMI. Roughly 340 extra calories a day.
- Third trimester
- About 1 lb a week. Roughly 450 extra calories a day.
- What the weight is
- The baby is only part of it. Placenta, amniotic fluid, increased blood volume, larger breasts and uterus, and fat stores all contribute.
What this assumes
These are the IOM 2009 guidelines for singleton pregnancies, and they are population recommendations rather than individual prescriptions.
Your clinician may advise differently based on your circumstances. Gestational diabetes, hyperemesis and other conditions all change the picture.
How to calculate pregnancy weight gain
Find your pre-pregnancy BMI, read off the range, and track against it rather than against a number.
- under 18.5
- 28-40 lb
- 18.5-24.9
- 25-35 lb
- 25-29.9
- 15-25 lb
- 30 and above
- 11-20 lb
Work out pre-pregnancy BMI. From your weight before pregnancy, not your current weight.
Read off the recommended total. The four bands above cover singleton pregnancies.
Understand the distribution. 1-4 lb in the first trimester, then roughly a pound a week afterwards at a normal starting BMI.
Track the trend, not individual weeks. Weekly weight fluctuates with fluid. What matters is the pattern across a month, and your provider will monitor it.
See a worked example: two different starting points
- Person A
- Pre-pregnancy BMI 22
- Person B
- Pre-pregnancy BMI 32
A: recommended total 25-35 lb, so 1-4 lb in the first trimester and about a pound a week after.
B: recommended total 11-20 lb, less than half of A's range.
Both are correct recommendations. The guidance is genuinely different, not a stricter version of the same advice.
Neither needs to double their food intake. The extra requirement is about 340 calories a day in the second trimester and 450 in the third.
25-35 lb at BMI 22, 11-20 lb at BMI 32
Frequently asked questions
It depends on your pre-pregnancy BMI. The IOM ranges are 28-40 lb if underweight, 25-35 lb at a normal BMI, 15-25 lb if overweight, and 11-20 lb if obese.
These are for a single baby. Twin pregnancies have separate, higher recommendations, and your provider may advise differently for your situation.
No, and the phrase is quantitatively misleading. The additional requirement is roughly 340 calories a day in the second trimester and 450 in the third, with no increase in the first.
That is a substantial snack, not a second meal. Nutrient quality matters more than quantity: folate, iron, calcium and protein all have raised requirements.
The baby is a minority of it. Placenta, amniotic fluid, increased blood volume, a larger uterus and breasts, and stored fat all contribute.
In a typical 30 lb gain the baby accounts for roughly a quarter. This is why weight does not disappear immediately after birth.
Raise it with your provider rather than adjusting your eating sharply on your own. Both excessive and insufficient gain carry risks, and the response depends on your circumstances.
Restrictive dieting during pregnancy is generally not advised. The usual approach is adjusting food quality and activity rather than cutting intake.
It is common, particularly with nausea and vomiting, and modest early loss is often not a concern.
Severe or persistent vomiting (hyperemesis gravidarum) is different and needs medical attention. If you cannot keep fluids down, contact your provider.
Some goes immediately: the baby, placenta and amniotic fluid account for around 12-14 lb at birth. Fluid loss continues over the following weeks.
The rest varies enormously and there is no standard timeline. Breastfeeding uses additional energy, and the effect on weight differs a lot between individuals.
Problems people actually run into
Using a single recommended figure
"25-35 lb" is the range for a normal pre-pregnancy BMI only. Someone starting at a BMI of 32 has a recommended range of 11-20 lb, less than half.
Work out pre-pregnancy BMI first. Applying the wrong band can mean substantially over- or under-gaining against genuine guidance.
Adding calories from the first trimester
There is no additional calorie requirement in the first trimester, and first-trimester gain is only 1-4 lb in total.
Eating for two from week five adds weight before any of it is needed. The increase belongs in the second and third trimesters.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Sources
- Weight Gain During Pregnancy · Centers for Disease Control and Prevention
Last updated: September 4, 2026