Pre-Pregnancy BMI Calculator
Work out your BMI from your weight before pregnancy and see the recommended total pregnancy weight gain for your category.
This calculator is for education only and is not medical advice. Please ask your doctor about a healthy weight gain for you.
- First, use this free Pre-Pregnancy BMI Calculator to work out your body mass index (BMI) from your weight before pregnancy.
- Next, enter your height and your pre-pregnancy weight.
- Then, you will see your BMI, your BMI category and the recommended total pregnancy weight gain for that category.
How to Use the Pre-Pregnancy BMI Calculator
You do not need any maths skills to use this calculator.
Simply follow these steps:
- First, choose your height unit: centimetres, or feet and inches.
- Then, enter your height. If you chose feet and inches, enter both the feet and the inches.
- Next, choose your weight unit: kilograms, or pounds.
- Then, enter your weight from before you became pregnant, not your current pregnancy weight.
- Then, press “Calculate my BMI”.
- Finally, read your result: your BMI to one decimal place, your category, and your recommended total pregnancy weight gain.
- Also, if you made a mistake, press “Reset” and start again.
Pre-Pregnancy BMI Categories
BMI is your weight in kilograms divided by your height in metres squared.
The categories below are the standard adult BMI categories.
In addition, they are used with the Institute of Medicine (IOM) pregnancy weight gain guidance.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy |
| 25–29.9 | Overweight |
| 30 or above | Obese |
What Your Result Means
- Underweight (below 18.5): Your pre-pregnancy BMI is below the healthy range.
- In general, people in this group are advised to gain more during pregnancy than people in higher BMI groups.
- This is because the baby and the pregnancy need extra energy and nutrients.
- Healthy (18.5–24.9): Your pre-pregnancy BMI is in the healthy range.
- Also, this is the range linked in population guidance with the lowest overall risk.
- However, every pregnancy is different.
- Overweight (25–29.9): Your pre-pregnancy BMI is above the healthy range.
- Therefore, the recommended total gain is lower than for the healthy range.
- However, it is still important to gain some weight during pregnancy.
- Obese (30 or above): Your pre-pregnancy BMI is in the obese range.
- As a result, the recommended total gain is the lowest of the four groups.
- Your doctor may also talk to you about blood sugar, blood pressure and birth planning.
- BMI is a simple screening tool.
- However, it does not measure body fat, muscle, bone, fluid or overall health on its own.
- So please treat the result as a starting point for a conversation with your doctor, not as a judgement about you.
Recommended Total Pregnancy Weight Gain
In addition, the table below shows the IOM recommended total weight gain for a pregnancy with one baby, based on pre-pregnancy BMI.
| Pre-pregnancy BMI category | Recommended total gain |
|---|---|
| Underweight (below 18.5) | 12.5–18 kg |
| Healthy (18.5–24.9) | 11.5–16 kg |
| Overweight (25–29.9) | 7–11.5 kg |
| Obese (30 or above) | 5–9 kg |
These ranges are for one baby.
However, twin pregnancies usually need a higher total gain.
Therefore, your doctor will set a personal target for you.
Frequently Asked Questions
What is pre-pregnancy BMI?
Pre-pregnancy BMI is your body mass index calculated from your height and your weight before you became pregnant.
In addition, it helps doctors and pregnancy guidance group people into categories for recommended weight gain.
How is BMI calculated?
BMI = weight in kilograms divided by height in metres squared.
For example, a person who weighs 62 kg and is 1.65 metres tall has a BMI of 22.8.
In fact, the calculation is 62 ÷ (1.65 × 1.65).
Therefore, this result is in the healthy range.
Should I use my current pregnancy weight or my pre-pregnancy weight?
Use your weight from before pregnancy for this calculator.
In addition, the recommended gain ranges are based on where you started.
So using your current weight would give the wrong category.
What if I do not know my exact pre-pregnancy weight?
Use the earliest weight you have from around the start of pregnancy.
For example, use your weight at your first pregnancy appointment.
Also, tell your doctor that it is an estimate.
Does a high or low BMI mean my pregnancy will have problems?
No.
BMI describes a range, not a diagnosis.
For example, many people outside the healthy range have healthy pregnancies.
Similarly, many people inside it still need extra care for other reasons.
Finally, your doctor looks at your full health picture.
Can I use this pre-pregnancy BMI calculator if I am carrying twins?
You can use it to find your BMI category.
However, the total gain ranges on this page are for one baby.
Therefore, ask your doctor for a twin pregnancy target.
Medical Disclaimer
This calculator and article are for education only and are not medical advice.
In addition, they do not replace professional care.
Therefore, please ask your doctor or midwife about a healthy weight gain target for you.
In particular, this is especially important if you have diabetes, high blood pressure, thyroid problems, an eating disorder, or any other health condition.
Related Calculators
- BMI Calculator — work out your current BMI at any time.
- Pregnancy Weight Gain Calculator — check your weight gain so far against a healthy range for your week.