How much pregnancy weight gain?
Enter your height, your weight before pregnancy, your weight now and the week of pregnancy. See the total gain the Institute of Medicine recommends for your BMI, and the range for this week.
- Recommended total gain
- 25 to 35 lb (11.5 to 16 kg)
With a pre-pregnancy BMI of 23.3 (Normal weight), the IOM recommends a total gain of 25 to 35 lb (11.5 to 16 kg).
- Pre-pregnancy BMI
- 23.3
- BMI category
- Normal weight
- Weekly gain, second and third trimesters
- 0.8 to 1 lb (0.35 to 0.50 kg) a week
- Range this week: from
- 7.4 lb
- Range this week: up to
- 12.4 lb
- Gained so far
- 12 lb
- Your gain so far
- Within the range for week 20
- Weeks
- 41
Recommended total gain: 25 to 35 lb (11.5 to 16 kg). With a pre-pregnancy BMI of 23.3 (Normal weight), the IOM recommends a total gain of 25 to 35 lb (11.5 to 16 kg).
How much gain is recommended by each week?
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Finds the recommended pregnancy weight gain for your pre-pregnancy BMI from the IOM 2009 guidelines, the range for your week of pregnancy, and whether your gain so far is within it.
Example with the default inputs (Height 5 ft 5 in, Weight before pregnancy 140 lb, Weight now 152 lb, Week of pregnancy 20, Babies One): With a pre-pregnancy BMI of 23.3 (Normal weight), the IOM recommends a total gain of 25 to 35 lb (11.5 to 16 kg).
Method: BMI = weight before ÷ height²; the IOM range for the BMI category; by week w: 0.5 × w ÷ 13 to 2 × w ÷ 13 kg up to week 13, then 0.5 + (w − 13) ÷ 27 × (total low − 0.5) to 2 + (w − 13) ÷ 27 × (total high − 2) kg up to week 40.
- The ranges are the Institute of Medicine 2009 guidelines, by pre-pregnancy BMI category (WHO cut-offs), read from the BMI shown to one decimal place.
- The week-by-week range is a straight line from nothing at conception to the IOM first-trimester gain (0.5 to 2 kg) at 13 weeks, then a straight line to the IOM total at 40 weeks.
- For twins the IOM gives only provisional total ranges, and none for an underweight BMI.
- This is general guidance, not medical advice; your provider may set a different goal.
Worked examples
Each example is checked against the calculator on every build.
- Height 5 ft 5 in, Weight before pregnancy 140 lb, Weight now 152 lb, Week of pregnancy 20, Babies One gives Pre-pregnancy BMI 23.3, BMI category Normal weight, Recommended total gain 25 to 35 lb (11.5 to 16 kg), Weekly gain, second and third trimesters 0.8 to 1 lb (0.35 to 0.50 kg) a week, Range this week: from 7.4 lb, Range this week: up to 12.4 lb, Gained so far 12 lb, Your gain so far Within the range for week 20.Source: Institute of Medicine 2009, Table S-1 (normal weight, 11.5 to 16 kg; first trimester 0.5 to 2 kg)
- Height 5 ft 3 in, Weight before pregnancy 176.4 lb, Weight now 180.8 lb, Week of pregnancy 10, Babies One gives Pre-pregnancy BMI 31.3, BMI category Obese, Recommended total gain 11 to 20 lb (5 to 9 kg), Range this week: up to 3.4 lb, Your gain so far Above the range for week 10.
- Height 5 ft 6.9 in, Weight before pregnancy 165.3 lb, Week of pregnancy 30, Babies Twins gives Pre-pregnancy BMI 26, BMI category Overweight, Recommended total gain 31 to 50 lb (14 to 23 kg).
How it works
1. Pre-pregnancy BMI = weight before pregnancy (kg) ÷ height (m)², rounded half up to one decimal place (the decimal value decides). The category is read from that rounded BMI: under 18.5 underweight; 18.5 to 24.9 normal weight; 25.0 to 29.9 overweight; 30.0 and over obese.
2. The IOM 2009 ranges (Table S-1, and the provisional ranges for twins):
| Pre-pregnancy BMI | Total gain, one baby | Weekly gain, 2nd and 3rd trimesters | Total gain, twins |
|---|---|---|---|
| Underweight | 28 to 40 lb (12.5 to 18 kg) | 1 to 1.3 lb (0.44 to 0.58 kg) | no IOM range |
| Normal weight | 25 to 35 lb (11.5 to 16 kg) | 0.8 to 1 lb (0.35 to 0.50 kg) | 37 to 54 lb (17 to 25 kg) |
| Overweight | 15 to 25 lb (7 to 11.5 kg) | 0.5 to 0.7 lb (0.23 to 0.33 kg) | 31 to 50 lb (14 to 23 kg) |
| Obese | 11 to 20 lb (5 to 9 kg) | 0.4 to 0.6 lb (0.17 to 0.27 kg) | 25 to 42 lb (11 to 19 kg) |
The headline shows the total gain as written in this table. For twins with an underweight BMI there is no answer, and for twins the weekly rows are left out.
3. The range by week (one baby), in kilograms, with the week w entered (0 to 42) and the total range low to high in kg from the table:
- up to week 13: from 0.5 × w ÷ 13 to 2 × w ÷ 13 (a straight line to the IOM first-trimester gain of 0.5 to 2 kg);
- from week 13 to week 40: from 0.5 + (w − 13) ÷ 27 × (low − 0.5) to 2 + (w − 13) ÷ 27 × (high − 2);
- after week 40: the total range.
4. Your gain so far = weight now − weight before pregnancy. It is compared with the range for the week in pounds rounded half up to one decimal place: below the range if the gain is less than the low end, above it if more than the high end, and within it otherwise (both ends included). The note reads "Within the range for week 20" and so on; after week 40 it names week 40, whose range (the IOM total) applies.
The chart shows the low and high ends of the range for each week from 0 to 40, in pounds.
Rounding. Every “rounded half up” on this page reads the decimal value: a result within 1e-9 (relative) of a half counts as the half. For example, 80 ÷ 1.6², which a computer stores as 31.249999999999993, rounds to 31.3.
Assumptions
- The IOM guidelines are for women in the United States and similar countries.
- The week-by-week lines are this calculator’s way to join the IOM first-trimester gain and the IOM total; the IOM gives no table for each week.
- This calculator gives general information. It is not medical advice; your provider may set a different goal for you.
Worked examples by hand
5 ft 5 in (1.651 m), 140 lb (63.503 kg) before pregnancy, 152 lb now, at 20 weeks. BMI = 63.503 ÷ 1.651² = 23.30, shown as 23.3: normal weight, so the total is 25 to 35 lb (11.5 to 16 kg). At week 20: low = 0.5 + 7 ÷ 27 × 11 = 3.352 kg (7.4 lb); high = 2 + 7 ÷ 27 × 14 = 5.630 kg (12.4 lb). Gain so far = 12 lb (5.443 kg): within the range for week 20.
1.60 m, 80 kg before pregnancy, 82 kg at 10 weeks. BMI = 80 ÷ 2.56 = 31.25, shown as 31.3: obese, total 11 to 20 lb (5 to 9 kg). At week 10 the range is 0.5 × 10 ÷ 13 = 0.385 kg to 2 × 10 ÷ 13 = 1.538 kg (3.4 lb). A gain of 2 kg (4.4 lb) is above the range for week 10.
Twins, 1.70 m and 75 kg before pregnancy. BMI = 75 ÷ 2.89 = 25.95, shown as 26.0: overweight, so the IOM twin range is 31 to 50 lb (14 to 23 kg).
Other questions people ask
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. The IOM 2009 guidelines for one baby: underweight (BMI under 18.5) 28 to 40 lb; normal weight (18.5 to 24.9) 25 to 35 lb; overweight (25.0 to 29.9) 15 to 25 lb; obese (30.0 and over) 11 to 20 lb.
How much should I gain each week?
After the first trimester, the IOM ranges per week are 1 to 1.3 lb (underweight), 0.8 to 1 lb (normal weight), 0.5 to 0.7 lb (overweight) and 0.4 to 0.6 lb (obese). The IOM assumes a gain of 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester.
How is the range for my week worked out?
The IOM gives totals and weekly rates, not a table for each week. This calculator draws a straight line from no gain at the start to the IOM first-trimester gain (0.5 to 2 kg) at 13 weeks, then a straight line from there to the IOM total at 40 weeks. The chart shows both lines.
What about twins?
The IOM gives provisional totals for twins: 37 to 54 lb for normal weight, 31 to 50 lb for overweight and 25 to 42 lb for obese. It gives no range for underweight women with twins, and no weekly ranges for twins.
Why is my BMI category based on my weight before pregnancy?
The guidelines are set by pre-pregnancy BMI, because body size before pregnancy changes how much gain is healthy. The categories are the WHO BMI cut-offs, read from the BMI to one decimal place.
I am above or below the range. What should I do?
Talk to your obstetric provider. Weight changes from week to week, and many things affect it. Your provider can look at your gain over time and set a goal for you.