About the Pregnancy Weight Gain Calculator
This calculator gives the recommended pregnancy weight gain range for your pre-pregnancy BMI, following Institute of Medicine guidelines, along with a target for your current week. Appropriate gain supports fetal growth while limiting complications for both mother and baby.
The formula
Total range depends on pre-pregnancy BMI categoryIOM recommendations: 12.5 to 18 kg for underweight, 11.5 to 16 kg for normal weight, 7 to 11.5 kg for overweight, and 5 to 9 kg for obese pre-pregnancy BMI.
How to use this calculator
- 1Enter your Pre-pregnancy Weight (kg). The field starts at
65, which you can overwrite. - 2Enter your Height (cm). The field starts at
165, which you can overwrite. - 3Enter your Current Week of Pregnancy. The field starts at
20, which you can overwrite. - 4Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Pre-pregnancy Weight (kg) | 65 |
| Height (cm) | 165 |
| Current Week of Pregnancy | 20 |
Result
Pre-pregnancy BMI: 23.9 (Normal weight)
Recommended Total Gain: 11.3–15.9 kg
Expected by Week 20: 3.4–5.3 kg
Remaining Recommended: 7.9–10.6 kg
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
Gain is not distributed evenly. The first trimester typically adds only 0.5 to 2 kg, with most accumulating in the second and third trimesters at roughly 0.4 to 0.5 kg per week for someone starting at a normal BMI. A slow first trimester is normal, particularly with nausea.
Both ends of the range carry risk. Insufficient gain is associated with low birth weight and preterm delivery; excessive gain raises the likelihood of gestational diabetes, hypertensive disorders, caesarean delivery, and postpartum weight retention. The recommended ranges reflect the point where both risks are lowest.
Things worth knowing
- Pregnancy raises calorie needs by roughly 340 kcal daily in the second trimester and 450 in the third — not double.
- Twin pregnancies have separate, higher recommendations: around 17 to 25 kg for a normal pre-pregnancy BMI.
- Sudden rapid gain with swelling can indicate pre-eclampsia and should be reported promptly.
- Protein, iron, folate, calcium, and iodine needs all rise. Diet quality matters as much as quantity.
- Weight loss during pregnancy is not recommended, even at a high starting BMI, without medical supervision.
Frequently asked questions
How much weight should I gain during pregnancy?+
It depends on your pre-pregnancy BMI: 11.5 to 16 kg for a normal BMI, 12.5 to 18 if underweight, 7 to 11.5 if overweight, and 5 to 9 if obese.
How much should I gain each week?+
Very little in the first trimester — 0.5 to 2 kg in total — then roughly 0.4 to 0.5 kg per week in the second and third for a normal starting BMI. Lower rates apply at higher starting BMI.
What if I am gaining too much or too little?+
Discuss it with your midwife or doctor rather than adjusting drastically on your own. Both insufficient and excessive gain carry risks, and guidance should be individual.
Do I need to eat for two?+
No. Energy needs rise by about 340 kcal daily in the second trimester and 450 in the third — roughly a substantial snack, not a second set of meals.