NHS Pregnancy BMI Calculator

Calculate your pre-pregnancy BMI and get guidance on healthy weight gain during pregnancy

Important Note

This calculator uses your pre-pregnancy weight to determine your BMI category before pregnancy. This is the standard approach used by the NHS and healthcare providers to recommend appropriate weight gain during pregnancy.

If you're already pregnant, enter your weight from before pregnancy or from your first antenatal appointment.

Height

Invalid height

Please enter either cm or feet/inches

Pre-Pregnancy Weight

Invalid weight

Please enter either kg or lbs

Current Week of Pregnancy Please enter a week between 1 and 42

Optional: Enter your current week of pregnancy to see recommended weight gain up to now

Number of Babies

Single pregnancy Multiple pregnancy (twins, triplets, etc.)

Relevant Medical Conditions (Optional)

Diabetes/Gestational Diabetes Hypertension Thyroid Disorder None of the above

Your Pre-Pregnancy BMI

kg/m²

BMI Category:

1st

First Trimester
(Weeks 1-12)

2nd

Second Trimester
(Weeks 13-26)

3rd

Third Trimester
(Weeks 27-40)

Postpartum
(After birth)

NHS Recommended Weight Gain:

Expected Weight Gain by Current Week:

Normal weight range (non-pregnant):

Expected total weight gain:

Pregnancy Nutrition and Health Advice:

Important Health Consideration:

Note: This calculator uses NHS guidelines to provide weight gain recommendations during pregnancy based on pre-pregnancy BMI. Individual needs may vary. Always consult your midwife or doctor for personalized advice.

BMI and Pregnancy: NHS Guidelines

Weight Gain

Nutrition

Health Risks

Postpartum

During pregnancy, NHS guidelines recommend different amounts of weight gain based on your pre-pregnancy BMI category.

Pre-pregnancy BMI Category	BMI Range	Recommended Total Weight Gain (Single Pregnancy)	Recommended Total Weight Gain (Multiple Pregnancy)
Underweight	Less than 18.5	12.5 - 18 kg (28 - 40 pounds)	No definitive guidelines, consult healthcare provider
Healthy Weight	18.5 - 24.9	11.5 - 16 kg (25 - 35 pounds)	17 - 25 kg (37 - 54 pounds)
Overweight	25 - 29.9	7 - 11.5 kg (15 - 25 pounds)	14 - 23 kg (31 - 50 pounds)
Obese	30 or higher	5 - 9 kg (11 - 20 pounds)	11 - 19 kg (25 - 42 pounds)

Weight Gain Pattern During Pregnancy

Healthy weight gain typically follows this pattern:

First Trimester: 0.5 - 2 kg (1 - 4.5 pounds)
Second Trimester: Approximately 0.5 kg (1 pound) per week
Third Trimester: Approximately 0.5 kg (1 pound) per week

There's no need to "eat for two" - you only need about 200 extra calories a day in the last trimester of pregnancy.

Where Does the Weight Go?

For a woman gaining 12 kg (26 pounds) during pregnancy, the weight is typically distributed as:

Baby: 3 - 3.5 kg (7 - 8 pounds)
Placenta: 0.7 kg (1.5 pounds)
Amniotic fluid: 0.8 kg (2 pounds)
Uterus: 0.9 kg (2 pounds)
Breast tissue: 0.45 kg (1 pound)
Blood volume: 1.2 kg (3 pounds)
Fluid retention: 1.2 kg (3 pounds)
Maternal fat stores: 3.5 kg (8 pounds)

Good nutrition during pregnancy is essential for both mother and baby's health, regardless of BMI category.

Nutritional Guidelines During Pregnancy

Calories: No extra calories needed in the first trimester, about 340 extra calories daily in the second trimester, and about 450 extra calories daily in the third trimester
Protein: Aim for 75-100g daily from sources like lean meat, poultry, fish, beans, tofu, and dairy
Folate/Folic Acid: 400 micrograms daily from leafy greens, fortified cereals, and supplements
Iron: 27mg daily from red meat, beans, fortified cereals, and possibly supplements
Calcium: 1,000mg daily from dairy products, fortified plant milks, and leafy greens
Vitamin D: 10 micrograms daily, primarily from supplements during UK winters

Foods to Avoid During Pregnancy

Unpasteurized dairy products
Raw or undercooked meat, poultry, eggs, and shellfish
High-mercury fish (shark, swordfish, marlin, tuna)
Raw sprouts
Excess caffeine (limit to 200mg per day)
Alcohol (no safe amount is known)

BMI-Specific Nutritional Advice

If Underweight:

Focus on nutrient-dense foods that provide healthy calories
Consider eating smaller, more frequent meals if you struggle with appetite
Ensure adequate protein intake for baby's development
Work closely with healthcare providers to monitor weight gain

If Overweight or Obese:

Focus on high-quality, nutrient-dense foods rather than calorie restriction
Choose complex carbohydrates over simple sugars
Maintain adequate protein intake
Include plenty of fruits, vegetables, and fiber
Stay well-hydrated with water rather than sugary drinks
Pregnancy is not a time for weight loss diets, but focusing on healthy eating patterns is beneficial

BMI before and during pregnancy can impact health risks for both mother and baby.

Health Considerations for Underweight Women (BMI < 18.5)

Being underweight before pregnancy may increase risks of:

Anemia
Preterm birth
Having a baby with low birth weight
Difficulties with breastfeeding
Longer recovery after birth

Health Considerations for Overweight Women (BMI 25-29.9)

Being overweight before pregnancy may increase risks of:

Gestational diabetes
High blood pressure during pregnancy
Preeclampsia
Longer labor
Higher likelihood of cesarean birth
Blood clots
Having a baby with higher birth weight

Health Considerations for Obese Women (BMI ≥ 30)

Being obese before pregnancy further increases all risks associated with being overweight, plus:

Miscarriage
Birth defects
Sleep apnea
Increased risk of stillbirth
Greater difficulty monitoring the baby during labor
Higher risk of post-birth infection

Reducing Risks Through Prenatal Care

Regardless of BMI, these measures can help reduce risks:

Attend all prenatal appointments
Take prenatal vitamins as recommended
Follow NHS guidelines for healthy eating during pregnancy
Stay physically active as advised by healthcare providers
Manage any existing health conditions
Report any concerning symptoms promptly to your healthcare provider

Weight management after pregnancy is an important aspect of postpartum health.

Postpartum Weight Loss Expectations

After giving birth, you'll immediately lose the weight of your baby, placenta, and amniotic fluid (about 4.5-5 kg or 10-12 pounds). Additional weight loss after birth varies:

Most women lose about half of their pregnancy weight gain by 6 weeks postpartum
Many women return to their pre-pregnancy weight by 6-12 months postpartum
Breastfeeding can help with postpartum weight loss, burning 300-500 extra calories per day
Weight retained more than a year after pregnancy is often associated with obesity in later life

NHS Recommendations for Healthy Postpartum Weight Loss

Wait until after your 6-week postnatal check before actively trying to lose weight
Aim for gradual weight loss of about 0.5-1 kg (1-2 pounds) per week
Focus on a balanced diet rich in fruits, vegetables, lean proteins, and whole grains
Stay hydrated, especially if breastfeeding
Begin gentle exercise when you feel ready and have been cleared by your healthcare provider
Build up exercise gradually, starting with walking and pelvic floor exercises
Avoid crash diets or very low-calorie diets, especially if breastfeeding

Planning for Future Pregnancies

If you're planning another pregnancy:

Try to reach a healthy weight before becoming pregnant again
Aim for a minimum of 12-18 months between pregnancies when possible
Take folic acid supplements for at least 3 months before conception
Discuss any weight or health concerns with your healthcare provider when planning your next pregnancy

Pregnancy BMI Calculator: Track Your BMI During Pregnancy with NHS Tools

What Is BMI and Why Is It Important During Pregnancy?

Body Mass Index (BMI) is a measurement used to assess body fat based on your weight and height. While BMI is important for everyone, it is especially useful during pregnancy to ensure both the mother and baby are healthy. Maintaining a healthy weight during pregnancy is vital to reduce the risk of complications such as gestational diabetes, high blood pressure, or preeclampsia.

Pregnancy changes the body significantly, and the NHS Pregnancy BMI Calculator helps you track weight changes while considering the specific needs of both the mother and developing baby. BMI during pregnancy is assessed using the same formula, but the interpretation takes into account the unique aspects of pregnancy.

How the NHS Pregnancy BMI Calculator Works

Using the NHS Pregnancy BMI Calculator

The NHS Pregnancy BMI Calculator allows expectant mothers to assess their weight relative to their height. To use the tool, you’ll need to provide the following information:

Pre-pregnancy Weight: Enter your weight before you became pregnant.
Current Weight: Enter your current weight, which includes any pregnancy-related weight gain.
Height: Provide your height in either centimeters (cm) or feet/inches (ft/in).
Stage of Pregnancy: Some tools allow you to specify the number of weeks of pregnancy, as weight gain recommendations can differ depending on the trimester.

Once entered, the calculator will calculate your BMI and categorize it to indicate whether your weight is in a healthy range for pregnancy.

What Does the BMI Result Mean for Pregnant Women?

Understanding Pregnancy BMI Categories

Pregnancy BMI results are categorized into four main ranges, similar to general BMI interpretations, but with adjustments for pregnancy:

Underweight: BMI below 18.5
Healthy Weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obese: BMI of 30 or higher

While these categories are similar to the general BMI categories, during pregnancy, it’s important to monitor healthy weight gain according to the guidelines provided by your healthcare provider. It’s normal for BMI ranges to shift during pregnancy, as some weight gain is necessary for the health of the baby.

Why Use the NHS Pregnancy BMI Calculator?

Benefits of the NHS Pregnancy BMI Calculator

The NHS Pregnancy BMI Calculator provides several key benefits for expectant mothers:

Track Healthy Weight Gain: The tool helps you monitor whether your weight gain during pregnancy is within the healthy range.
Informed Decision Making: Understanding your BMI helps you and your healthcare provider make decisions about nutrition, exercise, and overall pregnancy care.
Prevention of Pregnancy Complications: Maintaining a healthy BMI and weight gain helps reduce the risk of complications such as gestational diabetes, hypertension, and preeclampsia.
Personalized Guidance: The calculator can provide insights into whether your weight gain aligns with recommended guidelines for pregnancy.

How to Use the NHS Pregnancy BMI Calculator

Step-by-Step Guide to Using the Pregnancy BMI Calculator

Input Your Information: Enter your pre-pregnancy weight, current weight, height, and stage of pregnancy.
Get Your BMI Result: The calculator will calculate your BMI and place it in one of the pregnancy-specific categories.
Interpret the Result: Based on your BMI, you can understand whether your weight gain is within a healthy range.
Consult Your Doctor: If your BMI falls outside the healthy range, consult your healthcare provider for personalized recommendations and guidance on weight management during pregnancy.

Example: How the NHS Pregnancy BMI Calculator Works

Example Calculation:

Pre-pregnancy Weight: 60 kg
Current Weight: 70 kg (at 20 weeks pregnant)
Height: 165 cm

After entering these details into the NHS Pregnancy BMI Calculator, the result might show a BMI of 25.7, which falls into the overweight category. This indicates that while weight gain is a natural part of pregnancy, further monitoring and guidance may be required to ensure healthy pregnancy progression.

Healthy Weight Gain During Pregnancy

Understanding Weight Gain Guidelines

During pregnancy, it’s normal to gain weight, but the amount depends on several factors, including your pre-pregnancy BMI and the stage of pregnancy. The general guidelines for weight gain during pregnancy are as follows:

Underweight women (BMI less than 18.5): Gain 12.5 to 18 kg (28 to 40 lbs)
Normal weight women (BMI 18.5 to 24.9): Gain 11.5 to 16 kg (25 to 35 lbs)
Overweight women (BMI 25 to 29.9): Gain 7 to 11.5 kg (15 to 25 lbs)
Obese women (BMI 30 or higher): Gain 5 to 9 kg (11 to 20 lbs)

Your doctor may adjust these recommendations based on your specific health needs, but it’s important to avoid excessive weight gain, which can lead to complications.

Tips for Maintaining a Healthy BMI During Pregnancy

Healthy Lifestyle Choices for Expecting Mothers

Follow a Balanced Diet: Include plenty of fruits, vegetables, whole grains, and lean proteins in your meals. Avoid excessive sugary snacks and processed foods.
Exercise Regularly: Engage in safe activities such as walking, swimming, or prenatal yoga. Always consult with your healthcare provider before starting any new exercise routines.
Monitor Your Weight: Use the NHS Pregnancy BMI Calculator regularly to track your weight gain and make sure it aligns with healthy guidelines.
Stay Hydrated: Drink plenty of water throughout the day to stay hydrated and support your body’s needs during pregnancy.
Get Enough Sleep: Ensure you’re getting sufficient rest, as good sleep helps regulate hormones and supports a healthy pregnancy.

Final Words

Monitor Your Health with the NHS Pregnancy BMI Calculator

Using the NHS Pregnancy BMI Calculator is an excellent way to track your weight gain during pregnancy and ensure you’re staying within healthy limits. By understanding your BMI and following the guidelines for weight gain, you can reduce the risk of complications and support a healthy pregnancy for both you and your baby. Always consult with your healthcare provider for personalized recommendations.