Pregnancy weight gain calculator: the IOM 2009 ranges

Total gain range the IOM published for a pre-pregnancy BMI of 22.8worked example

11.5-16 kg

Pre-pregnancy BMI: 22.818.5 to 24.9
IOM category: Healthy weightthe report's own label: Normal weight
The other unit column, as printed: 25-35 lbthe report prints both columns independently
Cumulative range by week 20: 3-5.5 kg
Weight the range implies at term: 73.5 kg - 78 kg

These are the ranges the Institute of Medicine published in 2009 for a whole pregnancy, indexed by pre-pregnancy BMI - not weekly targets, and not a rule about any individual week. Gain is uneven, and the report’s own weekly figures assume 0.5-2 kg (1.1-4.4 lb) across the first trimester before they start.

Realistic range

3 kg to 5.5 kg

The cumulative range by week 20: the report's first-trimester allowance plus its weekly rate for the second and third trimesters, capped at the published total. A single week's weight is a noisy measurement, so the range matters more than the midpoint.

Weight before pregnancy (kg)The BMI categories are indexed on pre-pregnancy weight, not current weight.Height (cm)Used only to work out the BMI the IOM table is indexed by.Gestational weekFrom your due date, if you are not sure.Current weight (kg) - optionalOnly used to show where your gain sits against the week’s range.

Twin pregnancy (the report’s twin ranges are provisional)

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The 2009 IOM table, both columns as printed
Pre-pregnancy BMI	Total gain (kg)	Total gain (lb)	Rate in 2nd/3rd trimester	Twins (provisional)
Underweight (below 18.5)	12.5-18	28-40	0.44-0.58 kg/wk (1-1.3 lb/wk)	no range published
Healthy weight (18.5 to 24.9)	11.5-16	25-35	0.35-0.5 kg/wk (0.8-1 lb/wk)	16.8-24.5 kg (37-54 lb)
Overweight (25.0 to 29.9)	7-11.5	15-25	0.23-0.33 kg/wk (0.5-0.7 lb/wk)	14.1-22.7 kg (31-50 lb)
BMI 30.0 and above (30.0 and above)	5-9	11-20	0.17-0.27 kg/wk (0.4-0.6 lb/wk)	11.3-19.1 kg (25-42 lb)

Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009), Table S-1. BMI categories use the WHO cut-offs. Rate figures assume 0.5-2 kg (1.1-4.4 lb) in the first trimester. Twin ranges are provisional in the report itself, and no twin range is published below a BMI of 18.5.

The sources this defers to

ACOG: Weight Gain During Pregnancy — ACOG guidance built on the IOM 2009 ranges
CDC: Weight Gain During Pregnancy — the same ranges in patient-facing form
IOM/NRC, Weight Gain During Pregnancy: Reexamining the Guidelines (2009) — the report itself, including Table S-1 that this tool reproduces

The gestational week this needs comes from the due date calculator. After the birth, the same kind of maths - a measurement against a reference chart - is in the growth percentile calculator.

This applies the 2009 Institute of Medicine ranges: it works out your pre-pregnancy BMI, names the category the IOM puts that in, and shows the total gain range for the whole pregnancy plus the cumulative range by the week you enter. Twin ranges are included, and flagged as provisional by the report itself.

Gestational weight gain ranges (IOM 2009) — total gain by pre-pregnancy BMI: 12.5-18 kg, 11.5-16 kg, 7-11.5 kg, 5-9 kg. Verified 2026-07-30 against Institute of Medicine / National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009), Table S-1 (Population ranges for a pregnancy overall, not a target for any individual week. The report's own rate calculations assume a first-trimester gain of 0.5-2 kg (1.1-4.4 lb). The twin ranges are described by the report as provisional, and the report gives no range at all for a twin pregnancy beginning underweight.)

Everything you type here is computed in your browser. Nothing you enter is stored on a server, sent anywhere, or shared — there is no account and no health data to leak.

Frequently asked questions

How much weight gain do the guidelines describe?

The 2009 IOM ranges by pre-pregnancy BMI are 12.5 to 18 kg (28 to 40 lb) under a BMI of 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 to 29.9, and 5 to 9 kg (11 to 20 lb) at 30 and above.

Are those ranges in kilograms or pounds?

Both, and the report prints the two columns independently rather than converting one into the other. That is why 25 to 35 lb sits alongside 11.5 to 16 kg here: this tool reproduces the published columns exactly instead of doing its own conversion.

How is the weekly figure worked out?

The report assumes 0.5 to 2 kg (1.1 to 4.4 lb) across the first trimester, then a weekly rate for the second and third - for example 0.35 to 0.5 kg per week in the 18.5 to 24.9 category. The cumulative figure here is that assumption plus the weekly rate, capped at the published total.

What are the ranges for twins?

The 2009 report gives provisional twin ranges of 16.8 to 24.5 kg (37 to 54 lb), 14.1 to 22.7 kg (31 to 50 lb) and 11.3 to 19.1 kg (25 to 42 lb) for the three higher BMI categories. It gives no range for a twin pregnancy beginning under a BMI of 18.5, and neither does this tool.

What if my gain is outside the range?

The tool will tell you where the number sits and stop there. These are population ranges for a whole pregnancy, not weekly targets, and gain is not smooth. What a particular figure means is for the person doing your antenatal care, who can see everything this page cannot.

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The next number

No body metric means much on its own. Here is what this one feeds into.

Due date calculatorThe gestational week this tool needs comes from your due date.Growth percentile calculatorThe other side of the same maths, once the baby is here: a measurement against a reference chart.

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