Pregnancy Weight Gain Calculator
See your recommended pregnancy weight gain based on your pre-pregnancy BMI, how many weeks pregnant you are, and whether you are expecting one baby or twins, and check whether your gain so far is on track. Example: a woman with a normal BMI should gain 25 to 35 pounds in total, or about 14 to 21 pounds by week 28.
Show steps
How to use the Pregnancy Weight Gain Calculator
- Choose your units and enter your height and pre-pregnancy weight.
- Enter your current weight and how many weeks pregnant you are, and whether you are having twins.
- Press Calculate to see your BMI category, the recommended range for this week and whether you are on track.
Formula and method
Pre-pregnancy BMI = weight in kg / height in meters squared. The Institute of Medicine sets total gain by BMI group: underweight 28 to 40 lb, normal weight 25 to 35 lb, overweight 15 to 25 lb, obese 11 to 20 lb (one baby). For twins: normal 37 to 54 lb, overweight 31 to 50 lb, obese 25 to 42 lb. Gain in the first trimester is about 1.1 to 4.4 lb in total.
Recommended total weight gain (Institute of Medicine)
| Pre-pregnancy BMI | One baby | Twins | Weekly rate after week 13 (one baby) |
|---|---|---|---|
| Underweight (under 18.5) | 28 to 40 lb (12.5 to 18 kg) | Not established | 1 to 1.3 lb |
| Normal weight (18.5 to 24.9) | 25 to 35 lb (11.5 to 16 kg) | 37 to 54 lb (17 to 25 kg) | 0.8 to 1 lb |
| Overweight (25 to 29.9) | 15 to 25 lb (7 to 11.5 kg) | 31 to 50 lb (14 to 23 kg) | 0.5 to 0.7 lb |
| Obese (30 and over) | 11 to 20 lb (5 to 9 kg) | 25 to 42 lb (11 to 19 kg) | 0.4 to 0.6 lb |
Where the weight goes (full-term average)
| Source | Typical weight |
|---|---|
| Baby | 7.5 lb (3.4 kg) |
| Placenta | 1.5 lb (0.7 kg) |
| Amniotic fluid | 2 lb (0.9 kg) |
| Uterus | 2 lb (0.9 kg) |
| Breast tissue | 2 lb (0.9 kg) |
| Extra blood | 3 to 4 lb (1.4 to 1.8 kg) |
| Extra body fluid | 2 to 3 lb (0.9 to 1.4 kg) |
| Fat stores | 6 to 8 lb (2.7 to 3.6 kg) |
Gain by week for a normal BMI (one baby)
| Week | Expected range |
|---|---|
| Week 8 | 0.7 to 2.7 lb |
| Week 13 | 1.1 to 4.4 lb |
| Week 20 | 7.3 to 12.3 lb |
| Week 28 | 14.4 to 21.4 lb |
| Week 36 | 21.5 to 30.5 lb |
| Week 40 | 25.0 to 35.0 lb |
If you are gaining too much or too little
Gaining outside the range is linked with higher risks, such as preterm birth or a small baby when gain is low, and gestational diabetes, a large baby or cesarean delivery when gain is high. Do not diet during pregnancy. Eat a balanced diet, stay active as your provider advises, and ask about your own plan.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI: 25 to 35 pounds if you were a normal weight with one baby.
How much weight should I gain in the first trimester?
About 1 to 4 pounds in total.
How much should I gain per week?
About 1 pound a week in the second and third trimesters for a normal weight, less if you were overweight or obese.
How much weight should I gain with twins?
37 to 54 pounds for a normal BMI, 31 to 50 for overweight, and 25 to 42 for obese.
Is it bad if I gain too little?
Not always, but it can affect baby growth. Ask your provider.
What should I do if I am off track?
Do not diet or try to catch up quickly. Talk to your provider about food, activity and monitoring.
Sources
- National Academy of Medicine: Weight gain during pregnancy (2009)
- CDC: Weight gain during pregnancy
- ACOG: Healthy weight gain during pregnancy
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