Pregnancy weight gain calculator
This pregnancy weight gain calculator shows how much weight to gain by your current week and by the end of pregnancy. Enter your weight before pregnancy, your height and how many weeks pregnant you are: the calculator works out your pre-pregnancy BMI and the recommended range from the Institute of Medicine (IOM) guidelines.
Example: Units: pounds and inches · Weight before pregnancy 143 lb · Height 66 in · Weeks pregnant 20 → Recommended gain so far: 7.3 to 12.3 lb by week 20. Source: doi:10.17226/12584, Institute of Medicine / National Research Council (2009): Weight Gain During Pregnancy – Reexamining the Guidelines, Summary, Table S-1 (read 09.10.2026). Updated: .
How it is calculated
With a normal pre-pregnancy BMI (18.5 to 24.9) the recommended total weight gain is 25 to 35 lb (11.5 to 16 kg); by week 20 that means about 7.3 to 12.3 lb. Women who start out underweight should gain more, women with overweight or obesity less. The ranges come from the Institute of Medicine guidelines of 2009.
Recommended weight gain by BMI
| Pre-pregnancy BMI | Total gain (one baby) | Per week, 2nd and 3rd trimester | Twins (provisional) |
|---|---|---|---|
| below 18.5 (underweight) | 28–40 lb (12.5–18 kg) | 1 lb (1–1.3) | no guideline |
| 18.5–24.9 (normal weight) | 25–35 lb (11.5–16 kg) | 1 lb (0.8–1) | 37–54 lb (17–25 kg) |
| 25.0–29.9 (overweight) | 15–25 lb (7–11.5 kg) | 0.6 lb (0.5–0.7) | 31–50 lb (14–23 kg) |
| 30 or more (obese) | 11–20 lb (5–9 kg) | 0.5 lb (0.4–0.6) | 25–42 lb (11–19 kg) |
The guidelines assume a gain of 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester.
How the calculator works
- BMI = weight before pregnancy ÷ height². Example: 143 lb at 5 ft 6 in (66 in) gives a BMI of 23.1 – normal weight.
- Up to week 13 the range grows evenly to 1.1 to 4.4 lb.
- After that it rises evenly to the total range at week 40 (twins: week 37).
Week by week with a normal BMI
| Week | One baby | Twins |
|---|---|---|
| 13 | 1.1–4.4 lb | 1.1–4.4 lb |
| 20 | 7.3–12.3 lb | 11.6–18.9 lb |
| 24 | 10.8–16.9 lb | 17.6–27.1 lb |
| 28 | 14.4–21.4 lb | 23.5–35.4 lb |
| 32 | 17.9–25.9 lb | 29.5–43.7 lb |
| 36 | 21.5–30.5 lb | 35.5–51.9 lb |
| 40 | 25–35 lb | – |
Another example: 200 lb at 5 ft 4 in (BMI 34.3, obese) – about 6.6 to 13.1 lb by week 28 and 11 to 20 lb in total.
Find your current week with the pregnancy week calculator and your due date with the due date calculator.
Limits
The guidelines give ranges for the total gain. How weight builds up in between varies; the calculator assumes an even path. According to the IOM, the same ranges apply to teenagers and to women of short stature. The calculator does not replace prenatal care.
Frequently asked questions
How much weight should I gain during pregnancy?
25 to 35 lb with a normal BMI, 28 to 40 lb if underweight, 15 to 25 lb if overweight and 11 to 20 lb with obesity – based on your BMI before pregnancy.
How much weight should I gain per week?
Only 1.1 to 4.4 lb in the whole first trimester. From the second trimester about 1 lb a week (0.8 to 1 lb) with a normal BMI.
How much should I have gained by 20 weeks?
With a normal BMI about 7.3 to 12.3 lb (3.4 to 5.6 kg). This is an estimate based on the total range; single weeks can differ.
How much weight should I gain with twins?
The IOM gives provisional ranges: 37 to 54 lb with a normal BMI, 31 to 50 lb if overweight and 25 to 42 lb with obesity. There is no guideline for underweight women with twins.
Which weight do I use for BMI?
Your weight before pregnancy. If you are not sure, use the weight recorded at your first prenatal visit.
Sources and legal basis
- doi:10.17226/12584: Institute of Medicine / National Research Council (2009): Weight Gain During Pregnancy – Reexamining the Guidelines, Summary, Table S-1 (read 09.10.2026)
- IOM Report Brief (May 2009): Weight Gain During Pregnancy – recommendations in pounds, provisional guidelines for twins (read 09.10.2026)
As of: · Editorial policy
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