Pregnancy Weight Gain Calculator
Recommended pregnancy weight-gain range for your week, based on pre-pregnancy BMI.
Results update as you type.
About this calculator
A pregnancy weight-gain calculator shows the healthy amount to gain by any week of pregnancy, using the Institute of Medicine (IOM) guidelines that scale the target to your pre-pregnancy body mass index. Underweight women are advised to gain the most and obese women the least. First-trimester gain is small (about 0.5–2 kg); the bulk accrues in the second and third trimesters at a steady weekly rate, tracked here in a week-by-week schedule.
It first works out your pre-pregnancy BMI. A 165 cm, 60 kg woman has a BMI of 60 ÷ 1.65² ≈ 22, which is normal weight, so her full-term target is 11.5–16 kg. By week 20 the recommended gain is the small first-trimester amount plus about 0.35–0.5 kg per week for the seven weeks since week 13 — roughly 3–5.5 kg so far. The schedule lists the target for every fortnight of pregnancy.
Enter your height, pre-pregnancy weight and current week, and note whether you are carrying twins, which raises the recommended range substantially. Because these are population guidelines, individual advice may differ — your midwife or obstetrician accounts for your health, starting weight and how the pregnancy is progressing. This tool is for information, not medical advice.
Frequently asked questions
How much weight should I gain during pregnancy?
The IOM guidelines depend on pre-pregnancy BMI: about 12.5–18 kg (28–40 lb) if underweight, 11.5–16 kg (25–35 lb) if normal weight, 7–11.5 kg (15–25 lb) if overweight, and 5–9 kg (11–20 lb) if obese, for a single baby.
How is the weekly target worked out?
First-trimester gain is small — roughly 0.5–2 kg total. After week 13 a steady weekly rate applies (about 0.45 kg/week for normal weight, less if overweight), so the cumulative target at any week is the first-trimester gain plus the rate times the weeks since 13.
Is the guidance different for twins?
Yes. Carrying twins raises the recommended total substantially — roughly 17–25 kg (37–54 lb) for a normal-weight mother — because there are two babies plus extra placenta and fluid. This tool shows the higher twin range when selected.
How much weight should I have gained by 20 weeks?
For a normal-weight woman the IOM target by week 20 is roughly 3–5.5 kg (about 7–12 lb): the small first-trimester gain plus about 0.35–0.5 kg per week after week 13. The pregnancy weight gain calculator tailors this to your pre-pregnancy BMI.
Is it normal to lose weight in the first trimester?
Some women lose a little early on from nausea, which is often fine. The IOM plan expects only a small first-trimester gain of about 0.5–2 kg, with most weight added later; discuss significant loss with your provider.
What if I started pregnancy overweight or obese?
The recommended total is lower — about 7–11.5 kg if overweight and 5–9 kg if obese, versus 11.5–16 kg at a normal weight. The calculator picks the band from the height and pre-pregnancy weight you enter.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/pregnancy-weight-gain/curl
curl "https://calculator.free/api/v1/pregnancy-weight-gain/?units=metric&height=165&weight=60&week=20"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/pregnancy-weight-gain/?" + new URLSearchParams({
"units": "metric",
"height": "165",
"weight": "60",
"week": "20"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.