Pregnancy Weight Gain Calculator
See how much weight to gain in pregnancy from your pre-pregnancy BMI, using the 2009 IOM guidelines for one baby or twins, with a week-by-week chart.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Pregnancy Weight Gain Calculator?
This calculator works out your pre-pregnancy body mass index from your height and your weight before pregnancy, then shows the total weight gain recommended for that BMI group, the typical weekly rate in the second and third trimesters, and the cumulative range for the week you are in now. Add your current weight and it tells you whether your gain so far sits below, within or above that range, and plots you on a chart of the whole pregnancy.
The numbers are the 2009 guidelines from the Institute of Medicine (IOM, now the National Academy of Medicine), which ACOG and the CDC still use. They cover singleton pregnancies and give provisional ranges for twins. Switch between kilograms and centimetres or pounds, feet and inches; the calculator uses the published table for each unit rather than converting one into the other.
Guidelines describe what is associated with good outcomes across many pregnancies. Your own midwife or doctor may set a different target, and this page is not medical advice.
- Published IOM 2009 table in kg and lb
- Provisional twin ranges, with an honest gap for underweight twins
- Cumulative target range for any week with a chart
- Compares your current gain with the band
- Metric and US units with conversion when you switch
How to use the Pregnancy Weight Gain Calculator
- Choose metric or US units.
- Enter your height and your weight before pregnancy (or at the first appointment if you do not know it).
- Enter how many weeks pregnant you are, and switch on Expecting twins if that applies.
- Optionally enter your current weight to compare your gain with the range for this week.
- Read the BMI group, total and weekly targets, check the chart, and copy the plan if you want to share it.
Worked examples
Metric, healthy BMI
Input
165 cm, 65 kg before pregnancy, week 20
Output
BMI 23.9; total 11.5 to 16 kg; by week 20 about 3.4 to 5.6 kg
At 20 weeks seven of the 27 second-and-third trimester weeks have passed, so the band is the first-trimester allowance plus 7/27 of the remaining range.
US units, upper end of healthy
Input
5 ft 4 in, 140 lb, week 20
Output
BMI 24.0; total 25 to 35 lb; by week 20 about 7.3 to 12.3 lb
The calculator uses the IOM pound table (25 to 35 lb), not a conversion of 11.5 to 16 kg, so the figures match what US clinicians quote.
Twins
Input
5 ft 4 in, 160 lb, twins
Output
BMI 27.5, overweight; provisional total 31 to 50 lb
Twin totals are much higher than the singleton range of 15 to 25 lb for the same BMI.
Background and insight
The 2009 IOM report, Weight Gain During Pregnancy: Reexamining the Guidelines, replaced the 1990 version and switched to the WHO adult BMI cut-offs. Its Table S-1 recommends a total gain of 12.5 to 18 kg (28 to 40 lb) for an underweight BMI below 18.5, 11.5 to 16 kg (25 to 35 lb) for 18.5 to 24.9, 7 to 11.5 kg (15 to 25 lb) for 25 to 29.9, and 5 to 9 kg (11 to 20 lb) for 30 and above. The weekly rates for the second and third trimesters are 0.51, 0.42, 0.28 and 0.22 kg per week (about 1, 1, 0.6 and 0.5 lb), and they assume a gain of only 0.5 to 2 kg in the first trimester.
For twins the committee gave provisional totals at term: 17 to 25 kg (37 to 54 lb) for a normal BMI, 14 to 23 kg (31 to 50 lb) for overweight and 11 to 19 kg (25 to 42 lb) for obesity. It did not publish a twin range for an underweight BMI because there was not enough evidence, and this calculator says so rather than inventing one.
The IOM gives a total and a weekly rate but no single week-by-week curve. This page draws one by rising evenly to the first-trimester allowance at week 13 and then evenly to the total range at 40 weeks (37 for twins). That reproduces the published totals exactly and gives weekly slopes close to the published rates, so it is a fair way to see whether you are roughly on track.
Common use cases
Early pregnancy planning
Know your total target from the first appointment and what a typical week looks like.
Checking progress
Compare your weight at a checkup with the band for that week instead of guessing.
Twin pregnancies
See the provisional IOM range for twins, which few calculators include.
Talking with a dietitian
Bring a clear BMI group, target and chart to a nutrition appointment.
Tips and limitations
- Use your pre-pregnancy weight for BMI. Today's weight already includes pregnancy gain.
- Weigh at the same time of day in similar clothes; daily swings of a kilogram are normal.
- Nausea often means little or no gain in the first trimester, which the low end of the band allows for.
- A fast jump in weight over a few days, especially with swelling of the face or hands or a headache, needs prompt medical advice because it can signal pre-eclampsia.
- Energy needs rise modestly: roughly 340 extra kcal a day in the second trimester and 450 in the third for a singleton, according to the IOM dietary reference intakes.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. Under the 2009 IOM guidelines for one baby: 28 to 40 lb (12.5 to 18 kg) if underweight, 25 to 35 lb (11.5 to 16 kg) at a healthy BMI, 15 to 25 lb (7 to 11.5 kg) if overweight and 11 to 20 lb (5 to 9 kg) with obesity.
How much weight should I gain per week in the second and third trimesters?
About 1 lb (0.42 kg) a week at a healthy BMI, 1 lb (0.51 kg) if underweight, 0.6 lb (0.28 kg) if overweight and 0.5 lb (0.22 kg) with obesity. The first trimester usually adds only 1 to 4.4 lb in total.
How much weight should I gain with twins?
The IOM provisional ranges are 37 to 54 lb (17 to 25 kg) for a healthy BMI, 31 to 50 lb (14 to 23 kg) if overweight and 25 to 42 lb (11 to 19 kg) with obesity. There is no IOM range for underweight twin pregnancies, so a clinician should set the target.
Where does pregnancy weight go?
For a typical healthy-BMI singleton pregnancy at term, roughly 3.5 kg is the baby, 0.7 kg the placenta, 0.8 kg amniotic fluid, about 1 kg the enlarged uterus, 0.4 kg breast tissue, 1.5 kg extra blood and 1.5 kg other fluid, with the rest being fat stores that support breastfeeding.
Is it bad to gain less than the recommended range?
Gaining below the range is linked with a higher chance of a small baby and preterm birth, while gaining above it is linked with a large baby, caesarean birth and weight that stays after pregnancy. Being outside the band at one checkup is common; a sustained trend is worth discussing.
Which BMI should I use for the calculation?
Your BMI from before pregnancy, or from the first prenatal visit if you do not know it. The calculator works it out from your height and that weight using WHO adult cut-offs.
Is there an in-depth guide to the Pregnancy Weight Gain Calculator?
Yes. “How a Due Date Is Calculated, and How Much Weight to Gain” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
Related Tools You May Like
Free, in-browser tools that pair well with this one.