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 Rows: 11
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.
How much weight should you gain during pregnancy?
It depends on your BMI before pregnancy. The 2009 Institute of Medicine (IOM) guidelines recommend 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. At 165 cm and 60 kg, BMI is 22.0, so the range is 11.5–16 kg.
These ranges are for one baby carried to term. Twins have their own ranges, covered below.
Pregnancy weight gain by BMI
From the IOM report, Table S-1, with the weekly rate for the second and third trimesters:
Underweight (BMI under 18.5): 12.5–18 kg (28–40 lb) in total; 0.44–0.58 kg (1–1.3 lb) a week
Normal weight (18.5–24.9): 11.5–16 kg (25–35 lb); 0.35–0.50 kg (0.8–1 lb) a week
Overweight (25.0–29.9): 7–11.5 kg (15–25 lb); 0.23–0.33 kg (0.5–0.7 lb) a week
Obese (30.0 or more): 5–9 kg (11–20 lb); 0.17–0.27 kg (0.4–0.6 lb) a week
The report publishes metric and US figures separately, so they do not convert exactly: 25 lb is 11.3 kg, where the metric table says 11.5 kg. CDC's guidance uses the same ranges. One range covers every class of obesity.
How to work out your pre-pregnancy BMI
BMI is weight in kilograms ÷ height in meters squared: 60 ÷ 1.65² = 22.04, recorded as 22.0. Use your weight before pregnancy, not your current weight.
The BMI is rounded to one decimal before choosing the category, so 24.95 counts as 25.0 and falls in the overweight range of 7–11.5 kg.
Weight gain by week
Most of the gain comes after the first trimester. The IOM totals assume only 0.5–2 kg (1.1–4.4 lb) by the end of week 13, whatever the starting BMI; the weekly rates apply from week 14.
A week-by-week band can be drawn by joining those points with straight lines: from zero at week 0 to 0.5–2 kg at week 13, then on to the total at week 40. For a normal-weight start, that gives:
Week 8: 0.3–1.2 kg
Week 13: 0.5–2 kg
Week 20: 3.4–5.6 kg
Week 30: 7.4–10.8 kg
Week 40: 11.5–16 kg
The IOM itself publishes only the totals and the weekly rates. The straight lines rise 0.41–0.52 kg a week after week 13, close to its 0.35–0.50 kg rate for this group, so treat the band as a guide to the trend.
Twin pregnancy weight gain
The IOM set provisional ranges for twins carried to term (37–42 weeks):
Normal weight: 17–25 kg (37–54 lb)
Overweight: 14–23 kg (31–50 lb)
Obese: 11–19 kg (25–42 lb)
The committee found too little data to set a twin range for women who were underweight before pregnancy, and it gave no weekly rates for twins. If that applies to you, ask your clinician for a target.
Reading your gain so far
Gain so far is current weight minus pre-pregnancy weight. At week 20, a woman who started at 60 kg and now weighs 64.5 kg has gained 4.5 kg, inside the 3.4–5.6 kg band for that week.
A single weight outside the band is common. Clinicians look at the trend over several weeks, so a reading above or below it is something to discuss at your next appointment, not an amount to gain or lose quickly.
Three worked cases
Default: 165 cm, 60 kg before pregnancy, 64.5 kg at week 20.
Pound example: 64 in, 150 lb before pregnancy, 165 lb at week 30, using the IOM's US figures.
Term twins: 165 cm, 60 kg before pregnancy, 80 kg at week 37.
Scenario
Selected total range
Gain so far
Comparison
Default
11.5–16 kg
4.5
Within the range
Pound example
15–25 lb
15.0
Within the range
Term twins
17–25 kg
20.0
Within the term range
The pound example starts at a BMI of 25.7, which puts it in the overweight range. Its 15 lb gain at week 30 sits inside that week's band of 9.9–17.4 lb.
Entering weeks and units
Week of pregnancy is completed weeks since the first day of the last period, from 0 to 42; take it from your dating scan or due date.
Gains can be shown in kg or lb, and the choice also picks the IOM's metric or US table, separate from the units you weigh yourself in.
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.
About this calculator
gain(w)=⎩⎨⎧F13wF+(T−F)27w−13w≤1313<w≤40F=0.5–2kg,T=IOM total
For information only, not medical advice. These formulas describe populations, not you; talk to a clinician before acting on a result.
Checked against references
This calculator includes 7 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.
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