Pregnancy Weight Gain Calculator
Track recommended pregnancy weight gain by week based on your pre-pregnancy BMI.
Pre-pregnancy BMI
Total recommended gain
Full term
Recommended at current week
Your Progress
Your gain so far:
Understanding Pregnancy Weight Gain
Healthy weight gain during pregnancy supports your baby's growth and your own health, and lowers the risk of complications such as gestational diabetes, high blood pressure, preterm birth, and difficult delivery. The right amount of weight to gain depends largely on your body mass index (BMI) before pregnancy. This calculator uses the guidelines published by the Institute of Medicine (IOM, now the National Academy of Medicine) in 2009, which remain the standard recommendations used by clinicians worldwide.
IOM/NASEM Recommended Total Weight Gain (Singleton)
| Pre-pregnancy BMI | Category | Total gain (kg) | Total gain (lb) |
|---|---|---|---|
| Below 18.5 | Underweight | 12.5-18 | 28-40 |
| 18.5-24.9 | Normal weight | 11.5-16 | 25-35 |
| 25.0-29.9 | Overweight | 7-11.5 | 15-25 |
| 30.0 and above | Obese | 5-9 | 11-20 |
Recommended Total Weight Gain (Twins)
| Category | Total gain (kg) | Total gain (lb) |
|---|---|---|
| Normal weight | 16.8-24.5 | 37-54 |
| Overweight | 14.1-22.7 | 31-50 |
| Obese | 11.3-19.1 | 25-42 |
The IOM did not issue a specific twin range for underweight women due to insufficient data; normal-weight guidance is used as an approximation.
How the Calculation Works
Your pre-pregnancy BMI is calculated as weight (kg) / height (m)2, which places you in one of four categories. That category sets your total recommended gain for full term.
The recommendation for your current week follows the IOM pattern of weight gain. During the first trimester (weeks 1-13), total gain is small, roughly 0.5-2 kg (1-4.5 lb). From week 14 onward, a steady weekly rate is added based on your BMI category:
| Category | Weekly rate (kg/wk) | Weekly rate (lb/wk) |
|---|---|---|
| Underweight | 0.44-0.58 | ~1-1.3 |
| Normal weight | 0.35-0.50 | ~0.8-1 |
| Overweight | 0.23-0.33 | ~0.5-0.7 |
| Obese | 0.17-0.27 | ~0.4-0.6 |
The recommended range at your current week is the first-trimester baseline plus the weekly-rate range multiplied by the number of weeks past week 13. Your actual gain is your current weight minus your pre-pregnancy weight, and the assessment compares that figure against the current-week range.
References
The guidelines and ranges used in this calculator are based on the following sources:
- Institute of Medicine and National Research Council (2009). Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. DOI: 10.17226/12584
- American College of Obstetricians and Gynecologists (ACOG). Committee Opinion No. 548: "Weight Gain During Pregnancy." ACOG Committee Opinion 548
- Centers for Disease Control and Prevention (CDC). "Weight Gain During Pregnancy." CDC Pregnancy Weight Gain
Note: This calculator provides general estimates based on IOM/NASEM 2009 population guidelines and is not a substitute for individualized medical advice. Recommended weight gain can differ for your specific situation, including multiple pregnancies, pre-existing conditions, or adolescent pregnancy. Always discuss your weight gain goals with your obstetrician, midwife, or healthcare provider.
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