Pregnancy Weight Gain Calculator
Recommended pregnancy weight gain.
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Result
What is a Pregnancy Weight Gain Calculator?
A Pregnancy Weight Gain Calculator shows you the recommended weight-gain range for your stage of pregnancy based on your pre-pregnancy BMI and current week of gestation. It uses Institute of Medicine (IOM) guidelines to help you track whether your gain is on target.
How to calculate pregnancy weight gain manually (the formula)
First, calculate your pre-pregnancy BMI: BMI = weight (kg) ÷ height (m)². Then use the corresponding IOM guideline:
Underweight (BMI < 18.5): 0.44–0.58 kg/week in 2nd & 3rd trimester.
Normal (BMI 18.5–24.9): 0.35–0.50 kg/week.
Overweight (BMI 25–29.9): 0.23–0.33 kg/week.
Obese (BMI ≥ 30): 0.17–0.27 kg/week.
Example calculation
A woman with normal pre-pregnancy BMI (22) at week 28 should have gained approximately: 0.5–2 kg (first trimester) + (28 − 13 weeks) × 0.35 to 0.50 kg = 0.5–2 + 5.25–7.5 = 5.75–9.5 kg total by week 28.
Common mistakes
- Comparing to the wrong BMI category — Weight-gain recommendations differ substantially by pre-pregnancy BMI. Using the wrong category gives misleading targets.
- Not accounting for where you started — The recommendation is total gain from pre-pregnancy weight, not gain from your first prenatal visit. Always use your starting weight.
- Fretting over week-to-week fluctuations — Daily weight varies with fluid, food, and bowel movements. Focus on the overall trend rather than any single reading.
Frequently asked questions
How much weight should I gain during pregnancy?
Recommended gain depends on your pre-pregnancy BMI. Underweight: 12.5–18 kg. Normal weight: 11.5–16 kg. Overweight: 7–11.5 kg. Obese: 5–9 kg.
When does most pregnancy weight gain happen?
Most weight gain occurs in the second and third trimesters. First trimester gain is typically only 0.5–2 kg total. After that, about 0.5 kg per week for normal-weight women.
Is it safe to lose weight during pregnancy?
Weight loss during pregnancy is generally not recommended. If you are overweight, your doctor may suggest slower gain, but intentional weight loss can harm fetal development.
Where does pregnancy weight go?
Baby: 3–3.5 kg, placenta: 0.5–1 kg, amniotic fluid: 1 kg, uterine growth: 1 kg, breast tissue: 0.5 kg, blood volume: 1.5–2 kg, maternal fat stores: 2–4 kg.
What if I gain too much or too little?
Gaining too little increases the risk of a low-birth-weight baby. Gaining too much increases the risk of gestational diabetes, preeclampsia, and a large baby. Discuss your gain with your provider.
Does every pregnancy require the same weight gain?
No. Guidelines differ by pre-pregnancy BMI. Twin pregnancies require higher gain: 17–25 kg for normal-weight women carrying twins.