About the Pregnancy Weight Gain Calculator
This pregnancy weight gain calculator shows how much weight is recommended by your current week of pregnancy and in total, based on your height and pre-pregnancy weight. It works out your pre-pregnancy BMI, applies the Institute of Medicine (IOM, now the National Academy of Medicine) 2009 guidelines used by ACOG and the CDC, and compares your gain so far with the recommended range — for a single baby or twins.
Healthy gain depends on where you start: people who begin pregnancy underweight are advised to gain more (28–40 lb) and those with obesity less (11–20 lb). Most of the gain happens in the second and third trimesters; only about 1–4½ lb is expected in the first 13 weeks. The chart shows your week-by-week recommended band so you can see whether you are tracking within it.
The guidelines are ranges, not targets to hit exactly, and your provider may recommend something different for your situation. Use the result as a conversation starter at prenatal visits rather than a reason to diet during pregnancy.
How to use the pregnancy weight gain calculator
- 1Choose US or metric units.
- 2Enter your height and your weight before pregnancy.
- 3Enter your current weight and how many weeks pregnant you are.
- 4Switch on “Expecting twins” if applicable.
- 5Compare your gain so far with the recommended range and the chart.
Formula and method
Your pre-pregnancy BMI sets the IOM category and total recommended gain for a full-term (40-week) pregnancy: 28–40 lb if underweight, 25–35 lb for a healthy weight, 15–25 lb if overweight and 11–20 lb with obesity. For twins the provisional ranges are 37–54, 31–50 and 25–42 lb for healthy, overweight and obese BMI.
The IOM expects 1.1–4.4 lb (0.5–2 kg) in the first trimester, then a steady weekly gain. The calculator draws a straight line from 0 to that first-trimester range at week 13, then another from there to the total range at week 40, giving a low and high recommended cumulative gain for any week.
- w
- Weeks of pregnancy
- T1
- First-trimester gain (1.1 lb low, 4.4 lb high)
- Total
- IOM total gain range for your BMI category
Worked examples
5′5″, 140 lb before pregnancy, 155 lb at 24 weeks
A BMI of 23.3 is a healthy weight, so the total target is 25–35 lb. By week 24 the recommended gain is about 10.8–16.9 lb, and a 15 lb gain sits comfortably inside that range.
Overweight BMI, 30 weeks
At 64 inches and 170 lb, BMI is 29.2 (overweight), with a 15–25 lb total goal. The recommended gain at 30 weeks is about 9.9–17.4 lb, so a 26 lb gain is roughly 8.6 lb above the range.
Twins, metric, 20 weeks
A 21.3 BMI with twins gives a 37–54 lb (16.8–24.5 kg) total goal. At 20 weeks the recommended band is about 4.7–7.8 kg, so a 7 kg gain is right within it.
Frequently asked questions
How much weight should I gain during pregnancy?+
The IOM recommends 28–40 lb if you were underweight before pregnancy, 25–35 lb for a healthy BMI, 15–25 lb if overweight and 11–20 lb with obesity, for a single baby. Twin ranges are higher.
How much weight should I gain in the first trimester?+
Only about 1.1–4.4 lb (0.5–2 kg) in total. Many people gain little or even lose weight with nausea early on; most gain happens in the second and third trimesters.
How much weight should I gain per week?+
In the second and third trimesters the IOM suggests about 1 lb a week if underweight, 0.8–1 lb for a healthy BMI, 0.5–0.7 lb if overweight and 0.4–0.6 lb with obesity.
Where does pregnancy weight go?+
At term, typical gain includes the baby (7–8 lb), placenta, amniotic fluid, larger uterus and breasts, extra blood and fluid, and fat stores for breastfeeding — the baby is only about a quarter to a third of the total.
Is it safe to lose weight while pregnant?+
Dieting to lose weight is generally not recommended during pregnancy. If you have obesity your provider may advise gaining less than the standard range, but changes should be made with medical guidance.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.