Pregnancy Weight Gain Calculator

Track recommended weight gain during pregnancy based on your BMI and gestational week. Follows IOM/WHO guidelines.

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How Much Weight Should I Gain During Pregnancy?

The recommended weight gain during pregnancy depends on your pre-pregnancy Body Mass Index (BMI). The Institute of Medicine (IOM) and World Health Organization (WHO) provide guidelines to help ensure healthy outcomes for both mother and baby.

Weight gain that is too low can increase the risk of preterm birth and low birth weight. Excessive weight gain is associated with gestational diabetes, hypertension, and complications during delivery. The right amount varies for each person.

Weight Gain Guidelines by BMI Category

Based on IOM/WHO recommendations:

  • Underweight (BMI < 18.5): 12.5-18 kg total, ~0.51 kg/week in 2nd and 3rd trimesters
  • Normal weight (BMI 18.5-24.9): 11.5-16 kg total, ~0.42 kg/week in 2nd and 3rd trimesters
  • Overweight (BMI 25-29.9): 7-11.5 kg total, ~0.28 kg/week in 2nd and 3rd trimesters
  • Obese (BMI ≥ 30): 5-9 kg total, ~0.22 kg/week in 2nd and 3rd trimesters

When to Talk to Your Doctor

These are general guidelines — your healthcare provider may adjust recommendations based on your individual health, whether you're carrying multiples, or other factors. If you're gaining weight much faster or slower than recommended, discuss it at your next prenatal appointment.

How this tool works

How we calculate

The calculator works out your pre-pregnancy BMI (weight ÷ height²) and places it in the WHO categories: under 18.5; 18.5 to 24.9; 25 to 29.9; and 30 or more. For each category it uses the total gain recommended by the Institute of Medicine (IOM, 2009): 28–40 lb (12.5–18 kg), 25–35 lb (11.5–16 kg), 15–25 lb (7–11.5 kg), and 11–20 lb (5–9 kg). Pounds and feet are converted to kilograms and meters for the BMI.

The expected gain up to your week assumes 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester and, after that, the weekly rate recommended for each category, with a 20% margin either way.

Limitations

  • This follows the IOM 2009 guidelines used in the United States; other countries may use different charts (Brazil, for example, adopted national gestational weight gain curves in 2022).
  • It does not apply to twin pregnancies or to teenagers, who have their own recommendations.
  • BMI does not tell muscle from fat; your care team is the one who evaluates your weight gain.

Sources

  1. Institute of Medicine (2009) — Weight Gain During Pregnancy: Reexamining the Guidelines

Sources checked on November 6, 2026. How we produce our content

Frequently Asked Questions

How much weight should I gain in the first trimester?
Most women gain 0.5-2 kg (1-4.5 lbs) during the first trimester, regardless of BMI category. Weight gain is minimal early on, and some women even lose weight due to morning sickness. The majority of pregnancy weight gain occurs in the second and third trimesters.
Is it safe to lose weight during pregnancy?
Intentional weight loss during pregnancy is not recommended. However, some weight loss in the first trimester due to morning sickness is normal. If you're concerned about your weight, talk to your healthcare provider about healthy eating and exercise during pregnancy.
What if I'm gaining more weight than recommended?
Don't worry — these are guidelines, not strict rules. Focus on eating nutritious foods, staying active with your doctor's approval, and attending regular prenatal checkups. Your healthcare provider can help create a personalized plan.
Does pregnancy weight gain affect my baby?
Yes, appropriate weight gain supports your baby's healthy development. Insufficient gain may lead to low birth weight, while excessive gain is linked to larger babies and delivery complications. The recommended ranges are designed to optimize outcomes for both mother and baby.

Further reading

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