Pregnancy Weight Gain Calculator
Pregnancy weight gain ranges in kg or lb from pre-pregnancy BMI: total and weekly for one baby, total for twins, from the 2009 IOM guidelines. How it works
Use the Pregnancy Weight Gain Calculator
About the Pregnancy Weight Gain Calculator
The 2009 Institute of Medicine range for a single pregnancy depends on pre-pregnancy BMI: 12.5 to 18 kg (28 to 40 lb) below 18.5, 11.5 to 16 kg (25 to 35 lb) from 18.5 to 24.9, 7 to 11.5 kg (15 to 25 lb) from 25.0 to 29.9, and 5 to 9 kg (11 to 20 lb) at 30.0 and above. At 170 cm and 60 kg the BMI is 20.8, which gives 11.5 to 16 kg in total and 0.35 to 0.5 kg a week in the second and third trimesters. For twins the same BMI gives the report’s provisional 17 to 25 kg (37 to 54 lb).
Recommended gain by pre-pregnancy BMI (2009 Institute of Medicine, single pregnancy)
| Category | BMI | Total gain (kg) | Total gain (lb) | Per week, 2nd and 3rd trimester (kg) | Per week (lb) |
|---|---|---|---|---|---|
| Underweight | below 18.5 | 12.5 to 18 | 28 to 40 | 0.44 to 0.58 | 1 to 1.3 |
| Normal weight | 18.5 to 24.9 | 11.5 to 16 | 25 to 35 | 0.35 to 0.5 | 0.8 to 1 |
| Overweight | 25.0 to 29.9 | 7 to 11.5 | 15 to 25 | 0.23 to 0.33 | 0.5 to 0.7 |
| Obese | 30.0 and above | 5 to 9 | 11 to 20 | 0.17 to 0.27 | 0.4 to 0.6 |
The kilogram and pound columns are both taken from the published table, not converted from each other. The table assumes a first-trimester gain of 0.5 to 2 kg (1.1 to 4.4 lb).
Examples, as the calculator returns them
| Height and weight | BMI | Category | Total gain | Per week, 2nd and 3rd trimester |
|---|---|---|---|---|
| 160 cm, 50 kg | 19.5 | Normal weight | 11.5 to 16 kg | 0.35 to 0.5 kg |
| 170 cm, 60 kg | 20.8 | Normal weight | 11.5 to 16 kg | 0.35 to 0.5 kg |
| 175 cm, 55 kg | 18.0 | Underweight | 12.5 to 18 kg | 0.44 to 0.58 kg |
| 165 cm, 68 kg | 25.0 | Overweight | 7 to 11.5 kg | 0.23 to 0.33 kg |
| 160 cm, 90 kg | 35.2 | Obese | 5 to 9 kg | 0.17 to 0.27 kg |
| 5 ft 6 in, 150 lb | 24.2 | Normal weight | 25 to 35 lb | 0.8 to 1 lb |
| 5 ft 4 in, 185 lb | 31.8 | Obese | 11 to 20 lb | 0.4 to 0.6 lb |
| 5 ft 10 in, 120 lb | 17.2 | Underweight | 28 to 40 lb | 1 to 1.3 lb |
Metric inputs show kilograms and imperial inputs show pounds.
Provisional total gain for twins (2009 Institute of Medicine)
| Category | BMI | Total gain (kg) | Total gain (lb) |
|---|---|---|---|
| Underweight | below 18.5 | No guideline | No guideline |
| Normal weight | 18.5 to 24.9 | 17 to 25 | 37 to 54 |
| Overweight | 25.0 to 29.9 | 14 to 23 | 31 to 50 |
| Obese | 30.0 and above | 11 to 19 | 25 to 42 |
What the calculator shows with Twins selected. The report calls these ranges provisional, based on women who delivered twins of 2,500 g or more on average at 37 to 42 weeks; it had too little information for underweight women and gives no weekly rate for twins.
Lowest pre-pregnancy weight in each category, by height (kg)
| Height | Normal weight from | Overweight from | Obese from |
|---|---|---|---|
| 150 cm | 41.6 | 56.2 | 67.4 |
| 155 cm | 44.4 | 60.0 | 72.0 |
| 160 cm | 47.3 | 63.9 | 76.7 |
| 165 cm | 50.3 | 68.0 | 81.6 |
| 170 cm | 53.4 | 72.2 | 86.6 |
| 175 cm | 56.6 | 76.5 | 91.8 |
| 180 cm | 59.8 | 80.9 | 97.1 |
Found by trying every weight in steps of 0.1 kg in the calculator. Below the first column the category is Underweight. The category is read from the BMI rounded to one decimal, so the cut-offs sit slightly below a BMI of 18.5, 25 and 30 (a BMI of 24.96 shows as 25.0 and counts as Overweight).
Methodology
BMI = weight in kg ÷ (height in m)², with imperial heights converted at 2.54 cm per inch and weights at 0.45359237 kg per pound. The BMI is rounded to one decimal and that rounded value picks the category: below 18.5 Underweight, below 25 Normal weight, below 30 Overweight, otherwise Obese. The totals and weekly rates are the rows of Table S-1 in the Institute of Medicine report Weight Gain During Pregnancy: Reexamining the Guidelines (2009). With Twins selected the totals are the same report’s provisional twin ranges, with no weekly rate. For one baby, a week-by-week table spreads the first-trimester gain (0.5 to 2 kg, 1.1 to 4.4 lb) evenly over weeks 1 to 13 and adds the weekly rate for each week after; the IOM publishes no such curve, so the table is illustrative, and at a normal BMI its week 40 is 10.0 to 15.5 kg, below the 11.5 to 16 kg total. A BMI outside 12 to 60 gets no result.
How to use this tool
- Choose Metric (kg and cm) or Imperial (lb, feet and inches).
- Choose One baby or Twins.
- Enter your height and your weight from before the pregnancy.
- Read the BMI, its category, the total gain range for the pregnancy and, for one baby, the weekly rate for the second and third trimesters and the illustrative week-by-week table.
Frequently asked questions
- How much weight should I gain during pregnancy?
- The Institute of Medicine’s 2009 guidance for a single pregnancy is 11.5 to 16 kg (25 to 35 lb) at a pre-pregnancy BMI of 18.5 to 24.9, 12.5 to 18 kg (28 to 40 lb) below 18.5, 7 to 11.5 kg (15 to 25 lb) from 25.0 to 29.9 and 5 to 9 kg (11 to 20 lb) at 30.0 and above. These are published ranges, not a plan for you. Your midwife or doctor may advise a different amount.
- How much weight can I gain per week in the second and third trimester?
- For a pre-pregnancy BMI of 18.5 to 24.9 the table gives 0.35 to 0.5 kg (0.8 to 1 lb) a week. The other bands are 0.44 to 0.58 kg (1 to 1.3 lb) below 18.5, 0.23 to 0.33 kg (0.5 to 0.7 lb) from 25.0 to 29.9 and 0.17 to 0.27 kg (0.4 to 0.6 lb) at 30.0 and above. The table assumes 0.5 to 2 kg (1.1 to 4.4 lb) gained in the first trimester, which the calculator does not work out.
- How is my pre-pregnancy BMI worked out?
- Weight in kilograms divided by height in meters squared: 60 kg at 170 cm is 20.8, and 5 ft 6 in at 150 lb is 24.2. The BMI is rounded to one decimal before the category is chosen, so 165 cm and 68 kg shows 25.0 and counts as Overweight even though the unrounded value is 24.98.
- Why are the pound ranges not exact conversions of the kilogram ranges?
- Both columns are copied from the published table. 11.5 to 16 kg converts to 25.4 to 35.3 lb, while the table gives 25 to 35 lb, so the calculator shows 25 to 35 lb in imperial and 11.5 to 16 kg in metric.
- How much weight should I gain with twins?
- Choose Twins. The 2009 report gives provisional totals at term: 17 to 25 kg (37 to 54 lb) at a normal BMI, 14 to 23 kg (31 to 50 lb) overweight and 11 to 19 kg (25 to 42 lb) obese. It had too little information to give any range for an underweight woman carrying twins, and it gives no weekly rate for twins. There is no option for triplets or more.
- Is the week-by-week table an IOM chart?
- No. The IOM gives a first-trimester gain and a weekly rate for the second and third trimesters, not a curve. The table adds the two up week by week, so it is illustrative. Because the weekly rates are averages, week 40 can fall below the total range: at a normal BMI it comes to 10.0 to 15.5 kg against a total of 11.5 to 16 kg.
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