Prenatal Weight Gain Calculator
Estimate healthy pregnancy weight gain based on your pre-pregnancy BMI and track progress week-by-week. Guidance follows NHS practice for UK users and aligns with global (IOM/ACOG) recommendations for international audiences.
Note: Guidance shown is intended as a helpful estimate. For personalised advice and antenatal care, always consult your midwife, GP or obstetrician.
Prenatal Weight Gain Calculator: Track Healthy Weight During Pregnancy
Pregnancy is a time of incredible change, and one of the most important aspects of your journey is managing weight gain in a safe and healthy way. Our Prenatal Weight Gain Calculator helps expectant mothers estimate recommended weight gain during pregnancy based on pre-pregnancy BMI, using trusted NHS guidance for UK women and international standards (IOM and ACOG) for global audiences.
Whether you are in London, New York, Sydney, or anywhere in the world, Prenatal Weight Gain Calculator tool gives you a personalised recommendation and helps you understand progress week by week.
Why is weight gain important during pregnancy?
Gaining the right amount of weight in pregnancy supports your baby’s growth and reduces risks for both mother and child. Too little weight gain may lead to low birth weight, while too much can increase the chances of gestational diabetes, high blood pressure, or complications during birth.
The NHS notes that pregnancy usually requires little to no extra calories in the first trimester, with a gradual increase in the second and third trimesters. Globally, healthcare bodies such as the Institute of Medicine (IOM) and the American College of Obstetricians and Gynecologists (ACOG) also recommend weight ranges based on pre-pregnancy BMI.
How to use the Prenatal Weight Gain Calculator
Our calculator is simple, modern, and tailored for women in the UK and internationally:
- Select your measurement system
Choose between Metric (kg/cm), British (stone/pounds, feet/inches), or US (pounds, feet/inches). - Enter your pre-pregnancy weight and height
The calculator will work out your Body Mass Index (BMI), which is the basis for recommendations. - (Optional) Add your current pregnancy week or expected due date
This allows the tool to give you week-by-week guidance. - (Optional) Add your current weight
Track how much you’ve gained so far compared to your personalised range. - View your results
You’ll see:- Your BMI and category (underweight, healthy weight, overweight, or obese).
- Recommended total weight gain for your pregnancy.
- Your progress so far in percentage.
- A weekly target range if you entered your pregnancy week.
- Tips and advice based on NHS and global best practice.
Recommended pregnancy weight gain ranges
The tool uses widely accepted ranges based on pre-pregnancy BMI:
- Underweight (BMI < 18.5): 12.5–18 kg (28–40 lbs)
- Healthy weight (BMI 18.5–24.9): 11.5–16 kg (25–35 lbs)
- Overweight (BMI 25–29.9): 7–11.5 kg (15–25 lbs)
- Obese (BMI ≥ 30): 5–9 kg (11–20 lbs)
These ranges apply to single pregnancies. For twins or multiples, the recommendations differ, and you should always consult your healthcare professional.
Features of our Prenatal Weight Gain Calculator
- 🌸 Simple, feminine design that feels calm and welcoming.
- 🌍 Global measurement systems: UK metric, British stones/pounds, and US pounds.
- 📊 Week-by-week tracker: Helps you see whether you’re on track.
- 📑 PDF download option: Save your personalised pregnancy weight summary.
- 🔄 Built-in unit converter: Quickly switch between stones, pounds, kilos, and centimetres.
- 🧾 Trusted guidance: Based on NHS (UK), IOM (US), and global antenatal care advice.
Understanding pregnancy weight gain week by week
Weight gain in pregnancy is not steady – it changes as your baby develops:
- Weeks 1–12 (First trimester): Most women gain little or no weight; some may even lose weight due to morning sickness.
- Weeks 13–27 (Second trimester): Steady, gradual gain begins as your baby starts to grow quickly. Average gain is around 0.5–1 kg per week depending on your BMI.
- Weeks 28–40 (Third trimester): Growth continues, but the rate may slow towards the end as the baby reaches full size.
Other factors contributing to pregnancy weight include the placenta, amniotic fluid, increased blood volume, and natural fat stores to support breastfeeding.
Tips for healthy pregnancy weight gain
Our tool also provides general advice, but here are some key points from the NHS and international guidelines:
- Eat a balanced diet with a variety of fruits, vegetables, whole grains, lean proteins, and dairy.
- Avoid “eating for two” — most women only need a small calorie increase in the later stages.
- Stay active with safe exercises, such as walking, swimming, or prenatal yoga, unless advised otherwise.
- Drink plenty of water and stay hydrated.
- Attend regular antenatal appointments to monitor your weight and your baby’s growth.
Why choose this calculator?
Unlike basic BMI tools, this Prenatal Weight Gain Calculator is designed specifically for pregnancy, considering gestational week, current weight, and progress tracking. It’s tailored to meet the needs of both UK mothers following NHS standards and women globally following international recommendations.
With the ability to download results, track weekly changes, and switch between measurement systems, it’s one of the most engaging, SEO-friendly, and user-focused tools available online.
Related pregnancy tools you may find helpful
To support you further in your journey, explore these tools:
- 👶 Pregnancy Due Date Calculator
- 📅 Pregnancy Week-by-Week Tracker
- ❤️ Ovulation & Fertility Calculator
- 🍎 Healthy Pregnancy Meal Planner
- 🍼 Baby Kick Counter
- 🧘 Prenatal Exercise Guide
Final note
Every pregnancy is unique. This Prenatal Weight Gain Calculator gives you a helpful estimate, but your weight gain should always be monitored by your midwife, GP, or healthcare provider. For personalised advice, especially if you are expecting twins, have gestational diabetes, or other health concerns, professional medical guidance is essential.