# Pregnancy Weight Gain Calculator

> How much weight to gain in pregnancy depends on your BMI before you were pregnant: 25 to 35 lb for a normal BMI with one baby, more if your BMI was lower and less if it was higher. Enter your height and weight to see your range, and the healthy gain for the week you're in.

- Interactive calculator: https://www.leoella.com/tools/pregnancy-weight-gain-calculator
- Plain-text version: https://www.leoella.com/tools/pregnancy-weight-gain-calculator.md
- Category: Pregnancy
- Publisher: Leo&Ella (https://www.leoella.com)
- Last reviewed: October 19, 2026

## How it works

The calculator works out BMI from height and weight before pregnancy (weight in kilograms divided by height in meters squared) and places it in the WHO categories the IOM uses: under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 or more. It shows the IOM 2009 total gain range for one baby or twins. For one baby and the week entered, it draws a straight line from no gain to the assumed first-trimester gain (1.1 to 4.4 lb) at week 13, then on to the total range at week 40, and compares the gain so far with that week's range; twins get only the total range, because the IOM gives no weekly rates for twins.

## Key facts

- The Institute of Medicine (2009) recommends gaining 25 to 35 lb (11.5 to 16 kg) in a pregnancy with one baby for a pre-pregnancy BMI of 18.5 to 24.9. [2]
- For one baby, the IOM recommends 28 to 40 lb with a pre-pregnancy BMI under 18.5, 15 to 25 lb with a BMI of 25 to 29.9, and 11 to 20 lb with a BMI of 30 or more. [2]
- The IOM's provisional ranges for twins are 37 to 54 lb with a BMI of 18.5 to 24.9, 31 to 50 lb with a BMI of 25 to 29.9, and 25 to 42 lb with a BMI of 30 or more; it set no range for a BMI under 18.5. [2]
- The IOM guidelines assume a gain of 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester, then about 1 lb a week in the second and third trimesters for a normal pre-pregnancy BMI. [2]
- The CDC says the first trimester doesn't require any extra calories, and that you typically add about 340 calories a day in the second trimester and about 450 in the third. [3]

## Reference data

### IOM 2009 recommendations, one baby

| Pre-pregnancy BMI | Total gain | Total gain (kg) | Weekly in 2nd and 3rd trimesters, mean (range) |
| --- | --- | --- | --- |
| Underweight (BMI under 18.5) | 28 to 40 lb | 12.5 to 18 kg | 1 (1 to 1.3) lb; 0.51 (0.44 to 0.58) kg |
| Normal weight (BMI 18.5 to 24.9) | 25 to 35 lb | 11.5 to 16 kg | 1 (0.8 to 1) lb; 0.42 (0.35 to 0.5) kg |
| Overweight (BMI 25 to 29.9) | 15 to 25 lb | 7 to 11.5 kg | 0.6 (0.5 to 0.7) lb; 0.28 (0.23 to 0.33) kg |
| Obesity (BMI 30 or more) | 11 to 20 lb | 5 to 9 kg | 0.5 (0.4 to 0.6) lb; 0.22 (0.17 to 0.27) kg |

The IOM's calculations assume 1.1 to 4.4 lb (0.5 to 2 kg) in the first trimester.

### IOM 2009 provisional recommendations, twins

| Pre-pregnancy BMI | Total gain | Total gain (kg) |
| --- | --- | --- |
| Underweight (BMI under 18.5) | No IOM recommendation | No IOM recommendation |
| Normal weight (BMI 18.5 to 24.9) | 37 to 54 lb | 17 to 25 kg |
| Overweight (BMI 25 to 29.9) | 31 to 50 lb | 14 to 23 kg |
| Obesity (BMI 30 or more) | 25 to 42 lb | 11 to 19 kg |

### Healthy total gain so far by week, one baby (lb)

The calculator's straight-line estimate: from no gain to the first-trimester gain at week 13, then to the IOM total at week 40.

| Pre-pregnancy BMI | Week 13 | Week 20 | Week 26 | Week 30 | Week 36 | Week 40 |
| --- | --- | --- | --- | --- | --- | --- |
| Underweight (BMI under 18.5) | 1.1 to 4.4 lb | 8.1 to 13.6 lb | 14.1 to 21.5 lb | 18 to 26.8 lb | 24 to 34.7 lb | 28 to 40 lb |
| Normal weight (BMI 18.5 to 24.9) | 1.1 to 4.4 lb | 7.3 to 12.3 lb | 12.6 to 19.1 lb | 16.1 to 23.7 lb | 21.5 to 30.5 lb | 25 to 35 lb |
| Overweight (BMI 25 to 29.9) | 1.1 to 4.4 lb | 4.7 to 9.7 lb | 7.8 to 14.3 lb | 9.9 to 17.4 lb | 12.9 to 21.9 lb | 15 to 25 lb |
| Obesity (BMI 30 or more) | 1.1 to 4.4 lb | 3.7 to 8.4 lb | 5.9 to 11.9 lb | 7.3 to 14.2 lb | 9.5 to 17.7 lb | 11 to 20 lb |

### Healthy total gain so far by week, one baby (kg)

| Pre-pregnancy BMI | Week 13 | Week 20 | Week 26 | Week 30 | Week 36 | Week 40 |
| --- | --- | --- | --- | --- | --- | --- |
| Underweight (BMI under 18.5) | 0.5 to 2 kg | 3.6 to 6.1 kg | 6.3 to 9.7 kg | 8.1 to 12.1 kg | 10.7 to 15.6 kg | 12.5 to 18 kg |
| Normal weight (BMI 18.5 to 24.9) | 0.5 to 2 kg | 3.4 to 5.6 kg | 5.8 to 8.7 kg | 7.4 to 10.8 kg | 9.9 to 13.9 kg | 11.5 to 16 kg |
| Overweight (BMI 25 to 29.9) | 0.5 to 2 kg | 2.2 to 4.5 kg | 3.6 to 6.6 kg | 4.6 to 8 kg | 6 to 10.1 kg | 7 to 11.5 kg |
| Obesity (BMI 30 or more) | 0.5 to 2 kg | 1.7 to 3.8 kg | 2.7 to 5.4 kg | 3.3 to 6.4 kg | 4.3 to 8 kg | 5 to 9 kg |

## Frequently asked questions

### How much weight should I gain during pregnancy?

It depends on your BMI before pregnancy. For one baby, the Institute of Medicine (IOM) recommends 28 to 40 lb with a BMI under 18.5, 25 to 35 lb with a BMI of 18.5 to 24.9, 15 to 25 lb with a BMI of 25 to 29.9, and 11 to 20 lb with a BMI of 30 or more. The CDC uses the same ranges.

### How much weight should I gain with twins?

The IOM's provisional ranges for twins are 37 to 54 lb with a BMI of 18.5 to 24.9, 31 to 50 lb with a BMI of 25 to 29.9, and 25 to 42 lb with a BMI of 30 or more. There wasn't enough information to set a range for a BMI under 18.5, so your provider will set a goal with you.

### How much weight should I gain in the first trimester?

Not much. The IOM guidelines assume a gain of about 1.1 to 4.4 lb (0.5 to 2 kg) in the whole first trimester. Most of the gain comes in the second and third trimesters, at about 1 lb a week for a normal pre-pregnancy BMI.

### Why does the calculator use my weight before pregnancy?

The IOM ranges are set by body mass index (BMI) before pregnancy, which uses your height and pre-pregnancy weight. If you don't know your exact pre-pregnancy weight, use your best estimate and mention it to your doctor or midwife.

### What if I'm above or below the range?

Bring it up at your next appointment rather than making big changes on your own. Your doctor or midwife knows your health and how your baby is growing, and may set a different goal than the general IOM range.

### Do I need to eat for two?

No. The CDC says you don't need extra calories in the first trimester, and typically about 340 extra calories a day in the second trimester and about 450 in the third.

## Sources

1. [Institute of Medicine: Weight Gain During Pregnancy: Reexamining the Guidelines (2009), Report Brief](https://nap.nationalacademies.org/resource/12584/Report-Brief---Weight-Gain-During-Pregnancy.pdf)
2. [Institute of Medicine (2009): Summary and Table S-1](https://www.nationalacademies.org/read/12584/chapter/2)
3. [CDC: Weight Gain During Pregnancy](https://www.cdc.gov/maternal-infant-health/pregnancy-weight/index.html)

## About this page

This is general information for parents, not medical advice; a doctor, midwife or pediatrician who knows the family should guide individual decisions. The calculator runs in the visitor's browser and stores nothing they enter. When quoting this page, cite "Pregnancy Weight Gain Calculator, Leo&Ella" and link https://www.leoella.com/tools/pregnancy-weight-gain-calculator.