How much weight should I gain during pregnancy?

It depends on your pre-pregnancy BMI. The 2009 IOM guidelines for a single baby recommend roughly 12.5–18 kg if underweight, 11.5–16 kg at a healthy weight, 7–11.5 kg if overweight, and 5–9 kg if obese.

Does this work for twins?

No — these ranges are for a single baby. Twin pregnancies have higher targets, so follow the plan from your midwife or doctor.

How is the recommended range chosen?

It comes from your pre-pregnancy BMI band: underweight (BMI < 18.5), healthy (18.5–24.9), overweight (25–29.9) or obese (30+). Each band has its own total-gain target from the 2009 IOM guidelines.

How much should I gain per week in the later trimesters?

In the second and third trimesters the IOM suggests roughly 0.44–0.58 kg/week if underweight, 0.35–0.5 if healthy weight, 0.23–0.33 if overweight, and 0.17–0.27 if obese. Most weight gain happens after the first trimester.

How is my pre-pregnancy BMI calculated?

BMI is your pre-pregnancy weight in kilograms divided by your height in metres squared (kg/m²). The tool computes it from the height and pre-pregnancy weight you enter, in metric or imperial.

What if my gain is outside the range?

The range is a guide, not a strict rule. Being a little above or below is common and not necessarily a problem, but discuss any concerns about your weight gain with your midwife or doctor.

Is my data uploaded anywhere?

No. Every calculation runs in your browser and nothing is sent to a server.

Pregnancy Weight Gain Calculator

Q: How much should I gain per week in the later trimesters?

In the second and third trimesters the IOM suggests roughly 0.44–0.58 kg/week if underweight, 0.35–0.5 if healthy weight, 0.23–0.33 if overweight, and 0.17–0.27 if obese. Most weight gain happens after the first trimester.

Q: How is my pre-pregnancy BMI calculated?

BMI is your pre-pregnancy weight in kilograms divided by your height in metres squared (kg/m²). The tool computes it from the height and pre-pregnancy weight you enter, in metric or imperial.

Q: What if my gain is outside the range?

The range is a guide, not a strict rule. Being a little above or below is common and not necessarily a problem, but discuss any concerns about your weight gain with your midwife or doctor.

Q: Is my data uploaded anywhere?

No. Every calculation runs in your browser and nothing is sent to a server.

Pregnancy weight gain calculator

Healthy weight gain in pregnancy depends on your pre-pregnancy BMI and how far along you are. This calculator works out your BMI, your gain so far, and the expected range for your week using the 2009 Institute of Medicine (IOM) guidelines for a single baby — so you can see at a glance whether you are on track.

How it works

The tool computes your pre-pregnancy BMI, picks the matching IOM band, and compares your gain so far against that band’s total-gain range:

BMI         = pre-pregnancy weight (kg) ÷ height (m)²
gain so far = current weight − pre-pregnancy weight
band by BMI: <18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30+ obese

Recommended total gain (single baby, IOM 2009)

Pre-pregnancy BMI	Category	Total gain
< 18.5	Underweight	12.5–18 kg
18.5–24.9	Healthy weight	11.5–16 kg
25–29.9	Overweight	7–11.5 kg
30+	Obese	5–9 kg

Example

Height 1.65 m, pre-pregnancy weight 60 kg, current weight 68 kg:

BMI: 60 ÷ 1.65² = 60 ÷ 2.7225 ≈ 22.0 → healthy-weight band
Gain so far: 68 − 60 = 8 kg, within the 11.5–16 kg total target as the pregnancy progresses

Enter your numbers, drag the week slider, and see whether your gain is on track — all privately in your browser.