Pregnancy Weight Gain Calculator
Find the recommended weight-gain range for pregnancy from pre-pregnancy BMI.
Results update as you type.
This calculator provides estimates based on population research. Results are not medical advice. Consult a qualified healthcare provider before making health or nutrition decisions.
How it works
How much weight to gain during pregnancy is one of the most common questions expectant mothers ask, and a pregnancy weight gain calculator answers it using your body mass index before you conceived. The amount your body should gain over a full-term single pregnancy depends heavily on where you started: someone who began underweight needs to gain more to support a healthy baby, while someone who began with obesity is advised to gain less to reduce complications. This tool applies the widely used guidelines from the Institute of Medicine, now the National Academy of Medicine, which set recommended total gain ranges for each pre-pregnancy BMI category. It first computes your pre-pregnancy BMI from the weight and height you enter, then returns the recommended gain window in kilograms. Gaining within the recommended range supports the baby's growth and the mother's changing body, including the placenta, amniotic fluid, expanded blood volume, larger breasts and fat stores for breastfeeding, while lowering risks such as gestational diabetes, high blood pressure, a very large or very small baby, and difficult delivery. A pregnancy weight gain calculator gives a clear target range, but pregnancy is highly individual and gain is rarely steady week to week, tending to accelerate in later trimesters. These figures apply to a single baby; twins require more. Always use the result as general guidance and let your midwife or obstetrician tailor advice to your specific health, because they monitor the full picture that no calculator can see.
BMI = kg ÷ m²; IOM ranges: <18.5 → 12.5–18, 18.5–24.9 → 11.5–16, 25–29.9 → 7–11.5, ≥30 → 5–9 kg
The calculator first finds body mass index by dividing your pre-pregnancy weight in kilograms by the square of your height in metres, which sorts you into an underweight, normal, overweight or obese band. Each band maps to an evidence-based total weight-gain range established by the Institute of Medicine, because women who begin lighter can safely gain more to nourish the pregnancy, while those who begin heavier are advised to gain less to limit the risk of complications for both mother and baby.
Source:Institute of Medicine (IOM) pregnancy weight-gain guidelines
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter pre-pregnancy weight and height.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Recommended gain (low) updates instantly as you type — no button to press.
Frequently asked questions
Are these weight-gain ranges for a single baby or twins?
The ranges this calculator uses are for a single, full-term pregnancy. Carrying twins requires substantially more weight gain to support two babies, and the Institute of Medicine publishes separate, higher ranges for twin pregnancies, roughly 17 to 25 kilograms for a normal-weight mother. If you are expecting multiples, do not rely on the single-baby figures here; ask your obstetrician for the appropriate twin guidance tailored to your pre-pregnancy BMI.
What happens if I gain more than the recommended amount?
Gaining well above the recommended range raises the chance of gestational diabetes, high blood pressure, a larger baby that can complicate delivery, more caesarean sections, and greater difficulty losing the weight afterward. It can also increase the child's later risk of obesity. That said, one week of higher gain is not a crisis. Focus on the overall trend, eat nutrient-dense foods, stay active as advised, and let your care provider guide any adjustments rather than restricting sharply.
Is it dangerous to gain too little during pregnancy?
Yes, gaining too little can be harmful. Insufficient weight gain is linked to a higher risk of a low-birth-weight baby, preterm birth and problems with the baby's growth and development. Underweight mothers especially need adequate gain to support the pregnancy. If you are struggling to gain enough because of nausea, appetite loss or food access, tell your midwife or doctor, who can help with nutrition strategies and monitor the baby's growth closely to keep things on track.
When during pregnancy does most weight gain happen?
Weight gain is usually slow in the first trimester, often just half a kilogram to two kilograms total, then picks up in the second and third trimesters as the baby, placenta and fluids grow rapidly. A common pattern is around 0.4 to 0.5 kilograms per week in the later months for a normal-weight woman. Because the pace is uneven, judging progress against the total range and your provider's checks matters more than any single week's change.
Does the recommended gain include the baby's weight?
Yes. The recommended total is your whole-body gain, which includes the baby, the placenta, amniotic fluid, extra blood and fluid, the enlarged uterus and breasts, and maternal fat stores laid down for breastfeeding. The baby itself is only about three to four kilograms of the total. This is why the recommended figures are considerably larger than the baby's birth weight, and why most of the gain is normal, healthy and necessary rather than fat alone.