Pregnancy Weight Gain Calculator
Recommended weight gain for your BMI, total and by week
See the recommended total pregnancy weight gain for your pre-pregnancy BMI, the expected range at your current week, and how your gain so far compares, based on Institute of Medicine guidelines.
Health & FitnessUpdated October 21, 2026Checked against 6 reference values
Examples
Recommended total gain
25 to 35 lb
11.3 to 15.9 kg; pre-pregnancy BMI 22.8
Chart data as a table
| Week | Lower | Upper |
|---|---|---|
| 0 | 0 lb | 0 lb |
| 2 | 0 lb | 1 lb |
| 4 | 0 lb | 1 lb |
| 6 | 1 lb | 2 lb |
| 8 | 1 lb | 3 lb |
| 10 | 1 lb | 3 lb |
| 12 | 1 lb | 4 lb |
| 14 | 2 lb | 5 lb |
| 16 | 4 lb | 7 lb |
| 18 | 5 lb | 9 lb |
| 20 | 7 lb | 11 lb |
| 22 | 8 lb | 13 lb |
| 24 | 10 lb | 15 lb |
| 26 | 12 lb | 17 lb |
| 28 | 13 lb | 19 lb |
| 30 | 15 lb | 21 lb |
| 32 | 16 lb | 23 lb |
| 34 | 18 lb | 25 lb |
| 36 | 20 lb | 27 lb |
| 38 | 21 lb | 29 lb |
| 40 | 23 lb | 31 lb |
- Expected by week 20
- 6.7 lb (3.0 kg) to 11.4 lb (5.2 kg)
- BMI category
- Normal weight (BMI 18.5 to 24.9)
What this calculator does
Enter your weight before pregnancy, your height and how many weeks pregnant you are. The calculator works out your pre-pregnancy body mass index, shows the total weight gain recommended for that BMI, and gives the range expected by your current week. Add your current weight to see how your gain so far compares. A chart shows the recommended range week by week, with your own reading marked when you enter it. It covers single and twin pregnancies, using the guidelines from the Institute of Medicine (now the National Academy of Medicine), which the American College of Obstetricians and Gynecologists endorses.
Recommended gain by pre-pregnancy BMI
| Pre-pregnancy BMI | Total gain, one baby | Per week, 2nd and 3rd trimesters | Total gain, twins |
|---|---|---|---|
| Underweight (BMI below 18.5) | 28 to 40 lb (12.7 to 18.1 kg) | 1 to 1.3 lb | Not set |
| Normal weight (BMI 18.5 to 24.9) | 25 to 35 lb (11.3 to 15.9 kg) | 0.8 to 1 lb | 37 to 54 lb |
| Overweight (BMI 25 to 29.9) | 15 to 25 lb (6.8 to 11.3 kg) | 0.5 to 0.7 lb | 31 to 50 lb |
| Obesity (BMI 30 or more) | 11 to 20 lb (5.0 to 9.1 kg) | 0.4 to 0.6 lb | 25 to 42 lb |
Source: Institute of Medicine (2009). Twin ranges are provisional because fewer studies were available.
How the weekly range is worked out
BMI = weight (kg) ÷ height (m)²
expected gain at week w (after week 13) = first-trimester gain + (w − 13) × weekly rate
The IOM report assumes a total gain of 1.1 to 4.4 lb in the first 13 weeks, then a steady weekly gain through the second and third trimesters. The calculator spreads the first-trimester amount evenly over those weeks. For twins, where the IOM gives only totals, the range rises evenly from the end of the first trimester to week 40.
Worked example
A person who weighed 62 kg before pregnancy and is 1.65 m tall has a BMI of 22.8, in the normal range. The recommended total gain is 25 to 35 lb. At 20 weeks, the expected gain so far is about 6.7 to 11.4 lb (3.0 to 5.2 kg).
Where the weight goes
Only part of the gain is the baby. The rest is the placenta, amniotic fluid, a larger uterus and breasts, extra blood and fluid, and some stored fat that supports breastfeeding. This is why the recommended total is much more than the typical birth weight, and why gaining within the range supports a healthy pregnancy rather than simply adding fat.
Why the ranges matter
Research reviewed by the IOM linked gaining much less than recommended with a higher chance of a small baby and preterm birth, and gaining much more with a higher chance of a large baby, cesarean birth and keeping extra weight after pregnancy. The ranges are population guidance, not strict limits. Nausea in early pregnancy, swelling, and individual health conditions all affect the numbers, and your clinician may set a different target. Dieting to lose weight during pregnancy is not recommended unless a clinician advises it.
Practical notes
- Weigh yourself at the same time of day, in similar clothing, about once a week; daily readings bounce around with fluid.
- Use your weight from before pregnancy, not your weight at the first appointment, for the BMI.
- Energy needs rise only modestly: guidance often cited is about 340 extra calories a day in the second trimester and 450 in the third, with no extra needed in the first for most people.
- Talk to your clinician about rapid gain or sudden swelling, which can be a sign of a condition that needs checking promptly.
Pregnancy Weight Gain Calculator: common questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. The IOM recommends 25 to 35 lb for a normal BMI, 28 to 40 lb if underweight, 15 to 25 lb if overweight and 11 to 20 lb with obesity, for one baby.
How much weight should I gain each week?
Usually little in the first trimester, about 1 to 4 lb in total, then roughly 0.5 to 1 lb a week depending on your BMI category.
What about twins?
The IOM gives provisional totals for twins: 37 to 54 lb for a normal BMI, 31 to 50 lb if overweight and 25 to 42 lb with obesity. It did not set a range for underweight BMI.
I am below or above the range. Should I worry?
Weight gain varies, and one reading is not cause for alarm. Discuss it with your clinician, who can consider your health, the baby's growth and other factors.
Which weight should I use for BMI?
Use your weight just before pregnancy. Weight measured later in pregnancy would overstate your BMI category.
Sources
Related calculators
- Pregnancy Due Date CalculatorEstimate your due date from your last period, conception date, IVF transfer, a scan or a due date you were given, see how far along you are on any date, and check a scan against the ACOG redating rule.
- BMI CalculatorWork out your body mass index in metric or US units, see which WHO category it falls in, and find the healthy weight range for your height. Includes BMI Prime, the ponderal index and the WHO Asian cut-offs.
- Ovulation CalculatorEstimate your ovulation day and six-day fertile window from the first day of your last period and cycle length, with the next six cycles and a test date.
- Calorie CalculatorEstimate the daily calories that keep your weight steady and the target for any weekly pace of loss or gain, from Mifflin-St Jeor and your activity level, with the 1,200 and 1,500 kcal floors and a goal-weight timeline.
- Water Intake CalculatorEstimate how much water to drink each day from National Academies adequate intakes, adjusted for exercise, pregnancy and breastfeeding, in liters, ounces and cups.