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.

What is the Pregnancy Weight Gain Calculator?

Free pregnancy weight gain calculator. Enter your height, pre-pregnancy weight, current weight and week to see if your gain is on track for the recommended range. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Pregnancy Weight Gain Calculator

Name: Pregnancy Weight Gain Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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

Worked 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

Where does the weight go?

A common misconception is that pregnancy weight gain is entirely fat. In a typical single pregnancy for a healthy-weight person, the total gain is distributed across multiple components. The breakdown varies by individual, but roughly:

Baby — typically 3–4 kg at term
Placenta — around 0.6–0.7 kg
Amniotic fluid — around 0.8–1 kg
Uterus growth — around 0.9 kg
Breast tissue — around 0.4–1.4 kg
Increased blood volume — around 1.5 kg
Body fluid and tissue — around 1–2 kg
Maternal fat stores — 2.5–4 kg (varies most by individual)

This is why the IOM total-gain ranges are meaningful: they reflect what the body needs for fetal development and maternal physiology, not just caloric accumulation.

Rate of gain by trimester

Weight gain is not linear. The IOM guidelines describe how total gain distributes:

First trimester (weeks 1–13) — about 0.5–2 kg total in most women; morning sickness can temporarily reduce weight in this period.
Second and third trimesters — more consistent weekly gain, with the IOM suggesting a rate of roughly 0.35–0.5 kg/week for healthy-weight women. The rate differs by BMI band.

Pre-pregnancy BMI	2nd/3rd trimester rate
Underweight	0.44–0.58 kg/week
Healthy weight	0.35–0.50 kg/week
Overweight	0.23–0.33 kg/week
Obese	0.17–0.27 kg/week

If your gain is outside the range

The IOM ranges are guidelines, not strict cutoffs. Many women gain slightly above or below the range and have healthy outcomes. Discuss any concerns about pace of gain — too slow or too fast — with your midwife or obstetrician, who can assess your individual situation. Do not restrict food intake during pregnancy without clinical guidance.

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