Pregnancy Weight Gain Calculator

About this calculator

This calculator shows how much weight gain is recommended during pregnancy, based on your pre-pregnancy Body Mass Index (BMI). It applies the IOM/NASEM 2009 guidelines — the same ranges used by the CDC and ACOG — for both singleton and twin pregnancies, and reports the total recommended gain in kilograms and pounds plus the recommended weekly rate of gain in the second and third trimesters. Enter your pre-pregnancy weight and height; optionally add your current week and current weight to see whether your gain so far is below, on, or above the expected band.

How to read your results

The headline figure is your recommended total weight-gain range for the whole pregnancy, shown in both kg and lb. Your pre-pregnancy BMI places you in one of four categories — underweight, healthy weight, overweight, or obese — and each category has its own range: lower categories are advised to gain more, higher categories less. The weekly-rate figure applies only to the second and third trimesters, after a smaller first-trimester gain. If you add a current week and current weight, the calculator builds an expected band for that week and labels your progress as below, on track, or above it. These are population guidelines, not personal targets: healthy pregnancies occur across a range of gains, so use the result as a starting point for a conversation with your healthcare provider.

How it's calculated

Pre-pregnancy BMI is weight in kilograms divided by height in metres squared (BMI = kg ÷ m²); imperial inputs are converted to kg and cm first. The BMI is mapped to a category using the WHO adult cut-offs (under 18.5, 18.5–24.9, 25–29.9, 30+). Each category maps to the IOM/NASEM 2009 total-gain range and (for singletons) the published second/third-trimester weekly rate; twin ranges use the IOM provisional figures, with the underweight-twin case falling back to the CDC tracker estimate. The optional expected-by-week band assumes a first-trimester gain of 0.5–2 kg through week 13, then a straight-line progression to the full recommended total at week 40; your gain so far (current weight minus pre-pregnancy weight) is compared with that band to flag below / on track / above. Pounds are the canonical published figures; the kilogram ranges are the IOM-published kilogram values.

Worked example

A woman with a pre-pregnancy weight of 60 kg and height of 165 cm (BMI 22.0, healthy weight) is carrying one baby.

Her recommended total gain is 11.5–16 kg (25–35 lb), with a second/third-trimester rate of about 0.35–0.50 kg (0.8–1.0 lb) per week. At week 20 the expected cumulative gain is roughly 3.4–5.6 kg; a gain of 4 kg by then would be on track.

Frequently asked questions

How is the recommended weight-gain range decided?

It comes from your pre-pregnancy BMI. The IOM/NASEM 2009 guidelines set a different total-gain range for each BMI category: underweight (BMI under 18.5) 12.5–18 kg, healthy weight (18.5–24.9) 11.5–16 kg, overweight (25–29.9) 7–11.5 kg, and obese (30 or more) 5–9 kg for a singleton pregnancy. Women who start lighter are advised to gain more, and those who start heavier to gain less.

What about twins?

For twin pregnancies the IOM gives provisional total ranges: 17–25 kg (37–54 lb) for healthy weight, 14–23 kg (31–50 lb) for overweight, and 11–19 kg (25–42 lb) for obese. There is no IOM range for underweight women carrying twins because the evidence was insufficient, so for that case the calculator shows the CDC tracker estimate of 50–62 lb and flags it as an estimate.

What does the weekly rate mean?

After a small first-trimester gain (the IOM assumes about 0.5–2 kg in total over the first 13 weeks), most weight is gained at a steadier pace in the second and third trimesters. The weekly rate is the recommended pace for that later period — for example 0.35–0.50 kg per week for a healthy-weight singleton pregnancy. The IOM does not publish a weekly rate for twins, so that figure is derived from the total range and labelled accordingly.

I have gained more (or less) than the range — is something wrong?

Not necessarily. The ranges are population averages and good outcomes happen across a spread of gains. A reading outside the band is a prompt to discuss your pattern with your provider, who can weigh your individual circumstances — it is not a diagnosis. Sudden or rapid changes in weight are worth raising promptly.

Does this replace advice from my doctor or midwife?

No. This is a medical estimate built from published population guidelines, not personalised advice. Your provider sets your individual target taking into account your health history, how the pregnancy is progressing, and other factors the calculator cannot see.

Sources

• www.cdc.gov/maternal-infant-health/pregnancy-weight/index.html
• www.ncbi.nlm.nih.gov/books/NBK32799
• pmc.ncbi.nlm.nih.gov/articles/PMC2847829

Reviewed by the YouCalc Team · Last reviewedMay 24, 2026