How the recommended range is found
The calculator first works out your pre-pregnancy body mass index (BMI) by dividing your weight in kilograms by the square of your height in metres. That single number places you in one of four categories: underweight, normal, overweight, or obese.
Each category maps to a recommended total weight-gain range from the Institute of Medicine (IOM) 2009 guidelines for a single (non-twin) pregnancy. People who start at a lower BMI are advised to gain more, and those starting higher are advised to gain less, so that the baby and the pregnancy are well supported without excess.
What the week-by-week figure means
Weight gain is not spread evenly across pregnancy. The first trimester usually adds only a small amount — roughly half a kilogram to two kilograms — and most of the gain happens steadily through the second and third trimesters.
The "recommended gain so far" range applies that pattern to the gestational week you enter, giving an approximate target for where you might be at this point. The bar chart compares this so-far range against your full recommended total, so you can see how much of the journey it represents.
Using the result sensibly
These figures are population guidelines, not strict rules for any one person. Healthy pregnancies vary, and steady progress matters more than hitting an exact number in any given week.
- Expect normal week-to-week fluctuation rather than a perfectly smooth climb.
- The ranges here are for single pregnancies; carrying twins or more raises the targets.
- Focus on overall trend and nutrition rather than a single weigh-in.
- Sudden or rapid weight change can signal an issue and is worth reporting.
Medical disclaimer
This calculator provides general educational estimates based on IOM guidelines and is not a substitute for personalised medical advice. Recommended weight gain depends on your individual health, history, and circumstances. Discuss your weight-gain goals during pregnancy with your doctor, midwife, or another qualified healthcare provider.
Formula
BMI = weight / height²; total gain range from IOM bands; soFar scales with gestational weekFrequently asked questions
- Where do these ranges come from?
- They are the Institute of Medicine (2009) recommendations for total weight gain in a single (non-twin) pregnancy, grouped by pre-pregnancy BMI.
- Why is the week-by-week amount approximate?
- Weight gain is not perfectly linear and varies between people. The estimate assumes a modest first-trimester gain and steady gain afterward.