Pregnancy Weight Gain Calculator
Adjust the inputs below. Results update as you type.
How it works
IOM guidelines by pre-pregnancy BMI: underweight (<18.5): 28–40 lb total; normal (18.5–24.9): 25–35 lb; overweight (25–29.9): 15–25 lb; obese (≥30): 11–20 lb. Gain is minimal in the first trimester (1–4 lb), then about 1 lb/week in the second and third. Weight gain supports placenta, blood volume, amniotic fluid, and baby growth. Excessive or insufficient gain increases complications.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
Recommended gain depends on pre-pregnancy BMI: about 28–40 lb if underweight, 25–35 lb if normal, 15–25 lb if overweight, and 11–20 lb if obese, per common guidelines.
Worked example
A woman with a normal pre-pregnancy BMI is typically advised to gain 25–35 lb total, with most of it in the second and third trimesters.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
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Frequently asked questions
How much weight should I gain?+
It depends on your starting BMI. Normal-weight women are generally advised 25–35 lb; ranges shift lower for higher BMI and higher for underweight.
Is weight gain steady?+
Usually little gain in the first trimester, then roughly 0.5–1 lb per week in the second and third. Your provider tracks your individual pattern.
What if I am carrying twins?+
Recommended gain is higher for multiples. Discuss a personalized target with your healthcare provider.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.