ObstetricsAnthropometry and nutrition
Pregnancy weight gain calculator
Enter your height, pre-pregnancy weight, current weight and week of pregnancy. We calculate your pre-pregnancy BMI, the recommended gain for today and for the whole pregnancy, and show it on a chart.
Weight gain week by week
Source: Institute of Medicine (IOM) 2009. 0.5–2 kg in the first trimester, then linear to the total range.
Recommendations
Recommended weight gain depends on pre-pregnancy BMI: the higher the BMI, the smaller the recommended gain.
| Pre-pregnancy BMI | Total gain | Per week (2nd and 3rd trimester) | Twins |
|---|---|---|---|
| Underweight BMI < 18.5 | 12.5–18 kg | 0.44–0.58 kg | — |
| Normal weight BMI 18.5–24.9 | 11.5–16 kg | 0.35–0.50 kg | 17–25 kg |
| Overweight BMI 25.0–29.9 | 7–11.5 kg | 0.23–0.33 kg | 14–23 kg |
| Obesity BMI ≥ 30.0 | 5–9 kg | 0.17–0.27 kg | 11–19 kg |
The guidelines assume a gain of 0.5–2 kg in the first trimester. For twins they are provisional; for underweight women IOM gives no range because of insufficient data.
How we calculate
Pre-pregnancy BMI = pre-pregnancy weight [kg] ÷ height² [m²]. The recommended gain for a given week rises linearly from 0 to 0.5–2 kg by the end of week 13, then linearly to the total range at week 40. After week 40 we show the total range. Your gain = current weight − pre-pregnancy weight.
Limitations
- This is guidance, not a strict norm: weight gain is assessed by a doctor or midwife together with test results and the baby’s growth.
- Pre-pregnancy weight is often recalled from memory, which can shift the result by 1–2 kg.
- A sudden weight gain with swelling, especially in the second half of pregnancy, needs urgent assessment (it can accompany pre-eclampsia).
- The calculator does not apply to triplets or higher-order pregnancies.
Sources
- Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington (DC): National Academies Press; 2009. nap.nationalacademies.org
- ACOG Committee Opinion No. 548: Weight gain during pregnancy. Obstet Gynecol 2013;121:210–212. www.acog.org
- Gilmore LA, Redman LM. Weight gain in pregnancy and application of the 2009 IOM guidelines: toward a uniform approach. Obesity 2015;23:507–511. pmc.ncbi.nlm.nih.gov
Frequently asked questions
How much weight should I gain in pregnancy?
How much should I gain in the first trimester?
What about twins?
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This calculator is for education and does not replace a doctor’s assessment. Always interpret the result together with the history and examination.