Pregnancy Weight Gain Calculator
See the IOM recommended total weight gain for your pre-pregnancy BMI, and what that implies by a given week.
Result
Enter height and pre-pregnancy weight to see the result.
https://calcgallery.com/pregnancy/pregnancy-weight-gain-calculator/
How to use the Pregnancy Weight Gain Calculator
- Enter your height and your pre-pregnancy weight.
- Read the recommended total gain for the BMI band that puts you in.
- Optionally add the current week to see what the guidelines imply by this point.
- Optionally add your current weight to see the gain so far.
How it is calculated
Everything on this page follows from pre-pregnancy BMI, which is weight before pregnancy divided by height squared. That BMI is classified against the WHO bands — the same classification the BMI calculator uses — and the Institute of Medicine’s 2009 table is keyed on those bands.
Total recommended gain, from IOM/NRC Table S-1, for a singleton pregnancy:
| Pre-pregnancy BMI | Band | Total gain |
|---|---|---|
| Below 18.5 | Underweight | 12.5 to 18 kg |
| 18.5 to 24.9 | Normal weight | 11.5 to 16 kg |
| 25.0 to 29.9 | Overweight | 7 to 11.5 kg |
| 30.0 and above | Obese | 5 to 9 kg |
The three WHO obesity classes share one row in the IOM table, so this page collapses them the same way.
Expected gain by a given week. The first trimester is treated as a fixed total of 0.5 to 2 kg across every band, because early gain is small and does not vary much with starting BMI. From week 13 onward a weekly rate applies:
| Band | Rate per week |
|---|---|
| Underweight | 0.44 to 0.58 kg |
| Normal weight | 0.35 to 0.50 kg |
| Overweight | 0.23 to 0.33 kg |
| Obese | 0.17 to 0.27 kg |
expected by week W = first-trimester gain + rate × (W − 13)Before week 13 that second term is zero, so only the first-trimester range is reported.
Band boundaries are inclusive upward, the same rule the BMI page uses: a pre-pregnancy BMI of exactly 25.0 falls in the overweight row, not the normal one.
What this is and is not
This is a published population guideline, not a personal target. The IOM committee derived these ranges from outcomes across large groups of pregnancies. Antenatal care is individual, and advice from the clinician providing it supersedes a table.
Twin pregnancies are out of scope. The report publishes provisional ranges for twins and says so itself. Applying the singleton table to a twin pregnancy would be wrong, and presenting a provisional range next to a settled one without flagging the difference would be misleading, so this page covers singletons and says so.
Nothing here assesses whether a pregnancy is progressing normally, and no output on this page is a judgment about anyone’s weight.
Practical tips
Use a genuine pre-pregnancy weight. The whole table hangs off it, and a current weight will put you in the wrong band.
Gain is not smooth. It varies week to week and is often slower early and faster in the second trimester. A single reading against a weekly figure means very little.
The baby is a minority of the total. Placenta, fluid, blood volume and tissue growth account for most of the recommended gain.
A wide range is the honest form of this answer. Four and a half kilograms separate the ends of the normal-weight band.
Bring concerns to antenatal care, not to a calculator. This page reproduces a published table; it knows nothing about your pregnancy.
With your numbers
- So far the entered weights differ by 18 lb
- By the week entered the guidelines imply 9.6 lb to 16.5 lb
- A pre-pregnancy BMI of 22 is the normal weight row, where the IOM total is 25.4 lb to 35.3 lb
Quick reference
A published population guideline for singleton pregnancies, not a personal target. Twin ranges are provisional in the source itself and are not shown.
| Example | Recommended total gain, lower |
|---|---|
| 5 ft 5 in, 110 lb before, week 24 | 27.6 lb |
| 5 ft 5 in, 132 lb before, week 24 | 25.4 lb |
| 5 ft 5 in, 165 lb before, week 24 | 15.4 lb |
| 5 ft 5 in, 190 lb before, week 24 | 11 lb |
| 165 cm, 60 kg before, week 8 | 11.5 kg |
| 165 cm, 60 kg before, week 24 | 11.5 kg |
| 165 cm, 60 kg before, week 40 | 11.5 kg |
| 170 cm, 85 kg before, week 30 | 7 kg |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
4 sources
WHO Technical Report Series 894 (2000), Obesity: preventing and managing the global epidemic, Table 2.1, p. 9, https://iris.who.int/handle/10665/42330: underweight <18.50, normal range 18.50-24.99, preobese 25.00-29.99, obese class I 30.00-34.99, class II 35.00-39.99, class III ≥40.00.
Used for
- Upper boundary of the WHO underweight band.
- Lower boundary of WHO obesity class II.
- Lower boundary of WHO obesity class III.
WHO Technical Report Series 894 (2000), Obesity: preventing and managing the global epidemic, Table 2.1, p. 9, https://iris.who.int/handle/10665/42330: underweight <18.50, normal range 18.50-24.99, preobese 25.00-29.99, obese class I 30.00-34.99, class II 35.00-39.99, class III ≥40.00. The one-decimal edge is the one IOM/NRC, Weight Gain During Pregnancy (2009), Table S-1, p. 2, prints ("18.5-24.9 kg/m²"); health-shared.ts classifies below the next band's lower edge (25.0, 30.0), so both tables give the same band.
Used for
- Upper boundary of the WHO normal BMI band.
WHO Technical Report Series 894 (2000), Obesity: preventing and managing the global epidemic, Table 2.1, p. 9, https://iris.who.int/handle/10665/42330: underweight <18.50, normal range 18.50-24.99, preobese 25.00-29.99, obese class I 30.00-34.99, class II 35.00-39.99, class III ≥40.00. The one-decimal edge is the one IOM/NRC, Weight Gain During Pregnancy (2009), Table S-1, p. 2, prints ("25.0-29.9 kg/m²"); health-shared.ts classifies below the next band's lower edge (25.0, 30.0), so both tables give the same band.
Used for
- Upper boundary of the WHO overweight BMI band.
IOM/NRC, Weight Gain During Pregnancy (2009), Table S-1.
Used for
- Lower total gain for pre-pregnancy BMI below 18.5.
- Upper total gain for pre-pregnancy BMI below 18.5.
- Lower total gain for pre-pregnancy BMI 18.5 to 24.9.
- Upper total gain for pre-pregnancy BMI 18.5 to 24.9.
- Lower total gain for pre-pregnancy BMI 25.0 to 29.9.
- Upper total gain for pre-pregnancy BMI 25.0 to 29.9.
- Lower total gain for pre-pregnancy BMI 30 or above.
- Upper total gain for pre-pregnancy BMI 30 or above.
- Lower second and third trimester rate for pre-pregnancy BMI below 18.5.
- Upper second and third trimester rate for pre-pregnancy BMI below 18.5.
- Lower second and third trimester rate for pre-pregnancy BMI 18.5 to 24.9.
- Upper second and third trimester rate for pre-pregnancy BMI 18.5 to 24.9.
- Lower second and third trimester rate for pre-pregnancy BMI 25.0 to 29.9.
- Upper second and third trimester rate for pre-pregnancy BMI 25.0 to 29.9.
- Lower second and third trimester rate for pre-pregnancy BMI 30 or above.
- Upper second and third trimester rate for pre-pregnancy BMI 30 or above.
- Lower first-trimester total gain, applied to every BMI band.
- Upper first-trimester total gain, applied to every BMI band.
Common questions about the Pregnancy Weight Gain Calculator
- What if I am gaining faster than the range?
- That is a question for the person providing your antenatal care, not for a calculator. The IOM ranges are population guidelines derived from outcomes across large groups, and individual circumstances vary a great deal. Gain is also not linear or smooth week to week, so a single reading says much less than a trend over several appointments.
- Do the ranges apply to twins?
- The report publishes separate ranges for twin pregnancies and labels them provisional, because the evidence base was thinner. This page covers singleton pregnancies only and does not show twin ranges, because presenting a provisional figure alongside a settled one without that distinction would be misleading, and applying the singleton table to twins would be worse.
- What if I do not know my pre-pregnancy weight?
- A weight from early in the first trimester is a reasonable substitute, since gain over that period is small. If you have no figure at all, the band cannot be determined and neither can the range, because the entire table is keyed on pre-pregnancy BMI rather than on current weight.
- What makes up the weight gained?
- The baby is a minority of it. The rest is the placenta, amniotic fluid, an increased blood volume, additional fluid in the tissues, growth of the uterus and breasts, and maternal fat stores. That composition is why a total gain in the recommended range is expected rather than avoidable.
- Why is the recommended range narrower at higher BMI?
- The IOM ranges narrow and lower as pre-pregnancy BMI rises: 12.5 to 18 kg for underweight, down to 5 to 9 kg for obesity. The committee set them from outcome data across those groups. The report itself is the place to read the reasoning; this page reproduces the table and cites it.