Pregnancy Weight Gain Calculator
Enter your height, pre-pregnancy weight, current weight and week to see your BMI category, the recommended total and weekly weight gain from the IOM 2009 guidelines, and where you are on a week-by-week chart. Calculated privately in your browser.
General guidance for healthy adults, not medical advice. Your midwife or doctor may set a different target for you.
How to use the Pregnancy Weight Gain Calculator
- Choose units: lb and feet/inches, or kg and cm.
- Enter your height and pre-pregnancy weight (your weight before you became pregnant or at your first visit).
- Enter your current weight and how many weeks pregnant you are, and choose one baby or twins.
- Press Calculate weight gain to see your BMI category, the recommended total and weekly gain and your status for this week.
- Check the chart: the green band is the recommended range for each week and the orange dot is you.
IOM 2009 pregnancy weight gain guidelines
The ranges come from the Institute of Medicine (now the National Academy of Medicine) and National Research Council report Weight Gain During Pregnancy: Reexamining the Guidelines (2009), which is still the basis for advice from ACOG and the CDC in the United States. They are based on pre-pregnancy BMI (WHO categories).
| Pre-pregnancy BMI | Total gain, one baby | Weekly gain, 2nd–3rd trimester (mean, range) | Total gain, twins (provisional) |
|---|---|---|---|
| Underweight (< 18.5) | 28–40 lb (12.5–18 kg) | 1 lb (1–1.3) · 0.51 kg (0.44–0.58) | No guideline (insufficient data) |
| Normal (18.5–24.9) | 25–35 lb (11.5–16 kg) | 1 lb (0.8–1) · 0.42 kg (0.35–0.50) | 37–54 lb (17–25 kg) |
| Overweight (25.0–29.9) | 15–25 lb (7–11.5 kg) | 0.6 lb (0.5–0.7) · 0.28 kg (0.23–0.33) | 31–50 lb (14–23 kg) |
| Obese (≥ 30) | 11–20 lb (5–9 kg) | 0.5 lb (0.4–0.6) · 0.22 kg (0.17–0.27) | 25–42 lb (11–19 kg) |
The weekly rates assume a first-trimester gain of about 0.5–2 kg (1.1–4.4 lb). Some people gain little or even lose weight in the first trimester because of nausea, and that is usually not a concern.
How the calculator works
- BMI = pre-pregnancy weight (kg) ÷ height (m)². In imperial units, BMI = 703 × weight (lb) ÷ height (in)².
- Category is chosen from the BMI, which gives the total and weekly recommendation in the table.
- Range for your week: up to week 13 the band rises in a straight line to the first-trimester gain; from week 13 to 40 it rises in a straight line to the total range. This matches the IOM totals exactly and the weekly rates closely.
Example: 5 ft 5 in and 140 lb before pregnancy gives BMI 23.3 (normal), so the recommended total is 25–35 lb. At 20 weeks the recommended gain so far is about 7.3–12.3 lb; a gain of 12 lb is within range, leaving about 13–23 lb to gain by 40 weeks.
Tips and limits
- Weigh yourself at the same time of day, on the same scale, in similar clothes; day-to-day changes of 1–2 lb are just fluid.
- In the second and third trimesters, energy needs rise by roughly 340 and 450 kcal a day for one baby, not "eating for two".
- The guidelines apply to adults; teenagers, people with very high BMI (≥ 40) or with medical conditions may get individual advice.
- If you are curious about your BMI outside pregnancy, use the BMI calculator; to find how far along you are, use the due date calculator.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. For one baby, the Institute of Medicine (2009) recommends 28–40 lb (12.5–18 kg) if underweight, 25–35 lb (11.5–16 kg) with a normal BMI, 15–25 lb (7–11.5 kg) if overweight and 11–20 lb (5–9 kg) if obese.
How much weight should I gain each week?
In the first trimester most people gain only about 1–4.4 lb (0.5–2 kg) in total. In the second and third trimesters the IOM recommends roughly 1 lb (0.45 kg) a week for underweight and normal BMI, about 0.6 lb (0.28 kg) a week if overweight and 0.5 lb (0.22 kg) a week if obese.
What about twins?
For twins the IOM gives provisional total ranges: 37–54 lb (17–25 kg) for normal BMI, 31–50 lb (14–23 kg) for overweight and 25–42 lb (11–19 kg) for obese. There was not enough evidence to set a range for underweight women carrying twins, so ask your care provider.
Is it a problem if I am outside the range?
Not necessarily, and a single reading says little. Gaining well above or below the guidelines is linked with higher risks such as a large or small baby or a caesarean birth, so discuss it with your midwife or doctor rather than dieting during pregnancy. Never try to lose weight while pregnant unless your clinician advises it.
Where does pregnancy weight go?
At term, a typical gain is made up of the baby (about 7–8 lb), placenta, amniotic fluid, a larger uterus and breasts, extra blood and fluid, and maternal fat stores that support breastfeeding.
Why does the calculator use my pre-pregnancy weight?
The guidelines are based on BMI before pregnancy, because pregnancy itself increases weight. If you do not know it, use the weight measured at your first antenatal visit in early pregnancy.