About the Pregnancy Weight Gain Calculator
How much weight to gain in pregnancy depends mostly on your weight before you were pregnant. This pregnancy weight gain calculator works out your body mass index from your height and your weight before pregnancy, places you in a category, and shows the total weight gain recommended by the U.S. Institute of Medicine guidelines, for one baby or for twins. For one baby it also shows the usual weekly gain after the first three months and, if you enter the week you are in, the range you would expect so far and how your current weight compares. It is general information, and your midwife or doctor can advise on what is right for you.
Updated October 2026
How to use the Pregnancy Weight Gain Calculator
- 1Choose metric or imperial units.
- 2Enter your height and your weight before you were pregnant.
- 3Choose one baby or twins.
- 4Optionally enter your week of pregnancy and your current weight.
- 5Read the recommended total gain, the weekly rate and the range for your week.
How the categories work
- Underweight: BMI below 18.5
- Normal weight: BMI 18.5 to 24.9
- Overweight: BMI 25 to 29.9
- Obese: BMI 30 or more
- Use your weight before pregnancy, not your current weight, to find your BMI.
How the week-by-week range is worked out
In the first 13 weeks the guideline suggests a total gain of roughly 0.5 to 2 kg, spread evenly across those weeks. From week 14 the weekly gain for your category is added each week. At 28 weeks, a normal-weight woman would be expected to have gained about 5.8 to 9.5 kg. This is an average pattern, and many healthy pregnancies follow a different path.
Related tools
The Pregnancy Due Date Calculator works out your due date, the Conception Calculator estimates when you conceived, the BMI Calculator checks your body mass index, the Ideal Weight Calculator and Calorie Calculator are for non-pregnant adults and the Water Intake Calculator suggests daily fluids. Always follow the advice of your own healthcare team.
Features
- BMI and category before pregnancy
- Recommended total gain for one baby or twins
- Weekly gain after the first trimester
- Expected range for your week of pregnancy
- Comparison with your current weight
- Kilograms or pounds
- Runs in your browser
Frequently asked questions
How much weight should I gain in pregnancy?
For one baby the recommended total gain is 12.5 to 18 kg (28 to 40 lb) if you started underweight, 11.5 to 16 kg (25 to 35 lb) at a normal weight, 7 to 11.5 kg (15 to 25 lb) if overweight, and 5 to 9 kg (11 to 20 lb) if obese. These are general guidelines, and your own care team may advise something different.
How much should I gain each week?
In the first three months a gain of only about 0.5 to 2 kg (1 to 4 lb) in total is typical. After that, a normal-weight woman is advised to gain about 0.35 to 0.5 kg (0.8 to 1 lb) a week. The calculator shows the rate for your own category.
What about twins?
Women expecting twins are advised to gain more: 17 to 25 kg (37 to 54 lb) at a normal weight, 14 to 23 kg (31 to 50 lb) if overweight and 11 to 19 kg (25 to 42 lb) if obese. There is no firm range for twins if you began underweight, so ask your doctor. Week-by-week ranges aren't shown for twins.
What if I've gained more or less than the range?
Don't worry about a single number. Weight gain varies a lot from person to person and from week to week, and early nausea can make it uneven. If you are well outside the range for several weeks, mention it at your next appointment so your midwife or doctor can check how you and your baby are doing.
Where do the pregnancy weight gain figures go?
Roughly 3.5 kg goes to the baby, with the rest used by the placenta, amniotic fluid, bigger breasts and womb, extra blood and fluids and some body fat stores for breastfeeding. Gaining within the recommended range is linked with healthier outcomes for both mother and baby.
Should I diet if I gain too much?
No. Do not try to diet or restrict food in pregnancy without advice from your doctor or midwife. They can suggest healthy eating and safe activity if you're concerned. This calculator gives general guidance only and is not medical advice.