Recommended pregnancy weight gain by pre-pregnancy BMI (IOM 2009), for singletons or twins, with the weekly rate and a week-by-week chart of your gain.
With a pre-pregnancy BMI of 22.0 (normal weight), the IOM recommends 11.5–16 kg in total. By week 20 that means about 3.4–5.6 kg; your gain of 4.5 kg is within the range.
Recommended gain by week (normal weight)
Upper limitLower limit
Pre-pregnancy BMI category
Recommended gain and weight by week (11 rows)
Week
Gain from (kg)
Gain to (kg)
Weight from (kg)
Weight to (kg)
4
0.2
0.6
60.2
60.6
8
0.3
1.2
60.3
61.2
12
0.5
1.8
60.5
61.8
13
0.5
2.0
60.5
62.0
16
1.7
3.6
61.7
63.6
20 (now)
3.4
5.6
63.4
65.6
24
5.0
7.7
65.0
67.7
28
6.6
9.8
66.6
69.8
32
8.2
11.9
68.2
71.9
36
9.9
13.9
69.9
73.9
40
11.5
16.0
71.5
76.0
How it's calculated S
Pre-pregnancy BMI
(1.65m)260kg=22.04
Rounded to 22.0 and placed in the WHO/IOM band: Normal weight (18.5–24.9).
Recommended total gain (IOM 2009, Table S-1)
Normal weight: 11.5–16 kg in total; 0.35–0.50 kg a week (mean 0.42) in the second and third trimesters.
Gain so far
64.5−60.0=4.5kg
Recommended gain by week 20
0.5+(11.5−0.5)277=3.35to2+(16−2)277=5.63kg
Straight lines from 0 at week 0 to the IOM first-trimester assumption (0.5–2 kg) at week 13, then to the total at week 40. After week 13 they rise 0.41–0.52 kg a week, close to the IOM's separately published 0.35–0.50.
About the pregnancy weight gain calculator
The recommended total weight gain in pregnancy depends on BMI before pregnancy, using the 2009 Institute of Medicine (now National Academies) guidelines: 12.5–18 kg (28–40 lb) if underweight, 11.5–16 kg (25–35 lb) at a normal weight, 7–11.5 kg (15–25 lb) if overweight and 5–9 kg (11–20 lb) with obesity. In the second and third trimesters the report sets a weekly rate for each group, and it assumes 0.5–2 kg (1.1–4.4 lb) is gained in the first trimester. Twin pregnancies have provisional, higher ranges.
People use it to see whether their gain so far is on track. At the defaults, 60 kg before pregnancy at 165 cm (BMI 22.0) and 64.5 kg at week 20, the 4.5 kg gained sits inside the 3.4–5.6 kg band for that week.
The week-by-week band joins the first-trimester assumption at week 13 to the total range at week 40 with straight lines; the IOM itself publishes only the totals and the weekly rates.
It depends on your BMI before pregnancy. The 2009 IOM guidelines recommend 28–40 lb (12.5–18 kg) for a BMI under 18.5, 25–35 lb (11.5–16 kg) for 18.5–24.9, 15–25 lb (7–11.5 kg) for 25.0–29.9 and 11–20 lb (5–9 kg) for 30 or more. CDC's pregnancy weight gain trackers use the same ranges. A woman 165 cm tall who weighed 60 kg before pregnancy has a BMI of 22.0 and a target of 11.5–16 kg.
How much weight should you gain per week in pregnancy?
Little in the first trimester, about 0.5–2 kg (1.1–4.4 lb) in total, then a steady weekly amount. From week 14 the IOM rates are 0.44–0.58 kg (1–1.3 lb) a week if underweight, 0.35–0.50 kg (0.8–1 lb) at a normal weight, 0.23–0.33 kg (0.5–0.7 lb) if overweight and 0.17–0.27 kg (0.4–0.6 lb) with obesity.
How much weight should you gain with twins?
The IOM's provisional twin ranges, for a pregnancy reaching term at 37–42 weeks, are 37–54 lb (17–25 kg) at a normal pre-pregnancy weight, 31–50 lb (14–23 kg) if overweight and 25–42 lb (11–19 kg) with obesity. The committee found too little data to set a twin range for women who were underweight, and it gave no weekly rates for twins.
How much weight should you gain in the first trimester?
About 0.5–2 kg (1.1–4.4 lb) in total by the end of week 13, whatever the pre-pregnancy BMI. That is the assumption behind every total in the 2009 IOM table; the weekly rates only start in the second trimester. This calculator draws that gain as a straight line from week 0, which puts the band at 0.3–1.2 kg by week 8 and 0.5–2 kg by week 13.
How accurate is the pregnancy weight gain calculator?
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 7 worked examples whose answers come from independent sources; for example, “165 cm, 60 kg, week 20, now 64.5 kg” is checked against IOM 2009 Table S-1 (normal weight 11.5–16 kg, 0.35–0.50 kg/week). Python 3.8 fractions: 60/1.65² = 22.04; 0.5 + 11 × 7/27 = 3.3519; 2 + 14 × 7/27 = 5.6296.
Where does the method come from?
Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press, 2009 (Summary, Table S-1); CDC — Weight gain during pregnancy; Gilmore LA, Redman LM. Weight gain in pregnancy and application of the 2009 IOM guidelines: toward a uniform approach. Obesity 2015;23:507–511.
About this calculator
gain(w)=⎩⎨⎧F13wF+(T−F)27w−13w≤1313<w≤40F=0.5–2kg,T=IOM total