Pregnancy Weight Gain Calculator
See the IOM recommended pregnancy weight gain range for your pre-pregnancy BMI, what it implies by your current week, and where your gain so far sits. Singleton and twin, browser-only.
Results
Pregnancy weight gain calculator
This pregnancy weight gain calculator reports the range published by the Institute of Medicine for your pre-pregnancy BMI, what that range implies by the week you are at now, and where the weight you have gained so far sits against it.
Enter your height, your weight before pregnancy, your weight today and your completed week, and say whether you are carrying one baby or twins. It covers adults aged 18 to 50. It runs in your browser, with no account and nothing stored.
It is not antenatal care. The ranges below describe populations, not individuals, and your midwife or doctor may have good reasons to advise something different for you. Nothing on this page is a reason to change what you eat.
Pregnancy weight gain chart: recommended total by BMI
Weight gain during pregnancy is guided by your BMI before pregnancy, because BMI is not a suitable measure once you are pregnant. The pregnancy weight gain chart below is the published table for a single baby:
| Category | Pre-pregnancy BMI | Total gain | Total gain |
|---|---|---|---|
| Underweight | Below 18.5 | 12.5 to 18 kg | 28 to 40 lb |
| Normal weight | 18.5 to 24.9 | 11.5 to 16 kg | 25 to 35 lb |
| Overweight | 25.0 to 29.9 | 7 to 11.5 kg | 15 to 25 lb |
| Obesity | 30.0 and above | 5 to 9 kg | 11 to 20 lb |
The kilogram and pound columns are both as published. They are not conversions of one another, so the figures here match the ones a clinician is likely to quote in either unit.
This is also why a BMI calculator for pregnancy is not the tool to reach for. BMI in pregnancy rises by design, and reading it against the adult bands would classify a healthy pregnancy as overweight. A weight gain during pregnancy calculator instead takes the BMI you had beforehand, picks a range from it, and then tracks only what you have gained since.
How weight gain is expected to be paced
The guidance assumes most of the first trimester passes with little change, at 0.5 to 2 kg (1.1 to 4.4 lb) in total, and that steadier weekly gain follows through the second and third trimesters:
| Category | Per week | Per week |
|---|---|---|
| Underweight | 0.44 to 0.58 kg | 1 to 1.3 lb |
| Normal weight | 0.35 to 0.50 kg | 0.8 to 1 lb |
| Overweight | 0.23 to 0.33 kg | 0.5 to 0.7 lb |
| Obesity | 0.17 to 0.27 kg | 0.4 to 0.6 lb |
The calculator applies the first-trimester allowance for weeks 1 to 13, adds the weekly rate from week 14, and never lets the running range exceed the total for the whole pregnancy. Real gain is uneven, so a figure outside the range in any given week is common and is not, by itself, a problem.
Twin pregnancy weight gain
The IOM published a separate set of ranges for twins, and this calculator uses them when you select a twin pregnancy. They are labelled provisional in the source and are labelled provisional here, because they describe the middle half of gain observed among women who delivered twins at term rather than a range derived from outcomes:
| Category | Total gain | Total gain |
|---|---|---|
| Underweight | No guideline published | No guideline published |
| Normal weight | 17 to 25 kg | 37 to 54 lb |
| Overweight | 14 to 23 kg | 31 to 50 lb |
| Obesity | 11 to 19 kg | 25 to 42 lb |
The underweight row is empty because the source is empty. The committee stated that insufficient information was available to develop even a provisional guideline for underweight women carrying multiples, so this page reports that gap rather than borrowing the singleton figure or the next category up. If that is your situation, the range has to come from your own antenatal team.
Twin guidance is also a total and nothing else: no week-by-week rate was published alongside it. A twin result therefore shows the total range and no expected-gain-by-week figure, because pacing one would mean inventing a rate the evidence does not supply. Triplets and higher-order pregnancies have no IOM guideline at all and are outside this calculator.
The week-by-week chart
For a single baby, the result includes a chart of the recommended range across the whole pregnancy, with your own gain marked at the week you entered. The shaded band is flat through the first trimester, because the guidance treats those weeks as one allowance rather than a weekly rate, then widens from week 14 as the weekly range accumulates.
The band is drawn from exactly the figures the result reports, so the chart and the numbers beside it cannot disagree. Every figure it shows also appears as text, and the chart carries a description for screen readers, because a picture should never be the only place a number lives.
What this calculator does not do
It does not predict birth weight, gestational diabetes, pre-eclampsia, delivery outcome, or what you will weigh afterwards. It does not build a diet, and it will never suggest restricting intake or losing weight while pregnant.
It does not cover triplets or higher-order multiples, and it is not intended for pregnant adolescents, whose care is individualised. A gain outside the range is information to bring to an appointment, not a verdict on your pregnancy.
Sources and limitations
- Institute of Medicine and National Research Council: Weight Gain During Pregnancy, Reexamining the Guidelines (2009)
- CDC: weight gain during pregnancy
- CDC: adult BMI categories
Sources reviewed 27 August 2026. These are population ranges from 2009 guidance, published to balance the risks of gaining too little and too much across large groups. They cannot account for your medical history, and they are not a substitute for antenatal care.
Frequently asked questions
Is this antenatal care?
No. It reports the Institute of Medicine population ranges for a singleton pregnancy and where your gain sits against them. Your midwife or doctor knows your pregnancy, and their guidance takes precedence over anything shown here.
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. The Institute of Medicine ranges for a singleton pregnancy are 12.5 to 18 kg if you were underweight, 11.5 to 16 kg at a normal weight, 7 to 11.5 kg if overweight, and 5 to 9 kg with obesity. These are population ranges rather than targets set for you, and your midwife or doctor may advise something different for good reasons.
How is the expected range for my week worked out?
The guidance assumes 0.5 to 2 kg across the first trimester, then a steady weekly rate through the second and third. The calculator applies that allowance for weeks 1 to 13 and adds the weekly rate for your category from week 14 onward, capped at the recommended total for the whole pregnancy.
I have gained less than the range. Is something wrong?
Not necessarily, and this page cannot tell you. Gain is uneven, early-pregnancy sickness commonly causes loss, and a single reading says little on its own. What the range is useful for is starting a conversation: bring it to your next antenatal appointment, where someone who knows your pregnancy can interpret it.
I have gained more than the range. Should I diet?
This calculator does not give dietary advice and no web page should tell you to restrict intake while pregnant. Deliberate weight loss during pregnancy is something to discuss with a midwife or doctor, never to start from a calculator result.
Does this work for twins?
Yes, for the categories the IOM published. Select a twin pregnancy and the calculator uses the provisional twin ranges: 17 to 25 kg at a normal pre-pregnancy BMI, 14 to 23 kg if overweight, and 11 to 19 kg with obesity. No guideline was published for twins beginning at an underweight BMI, and the page says so rather than showing a substitute. Triplets and above have no guideline at all.
Why is there no week-by-week range for twins?
Because none was published. The IOM gave twin totals without a rate-of-gain table, so there is no source for what a twin pregnancy should have gained by any given week. Estimating one would mean inventing guidance, so the twin result shows the total range and stops there.
Why does it ask for my pre-pregnancy weight?
Because the recommended range is selected by your BMI before pregnancy, not your BMI now. BMI is not a suitable measure during pregnancy, which is why the calculator uses the earlier figure to pick a category and then works only in weight gained.
Related calculators
- BMI Calculator
- Healthy Weight Calculator (route pending)
- Calorie Calculator