Pregnancy Weight Gain Calculator

Enter your pre-pregnancy weight, current weight and week — see the official healthy gain range for right now and for the whole pregnancy.

Your details

Weight gained so far

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Fill in your weights on the left.

Pre-pregnancy BMI—
BMI category—
Recommended total gain—
Healthy range by week 20—
Where you stand—
Typical rate from here—

Ranges are the Institute of Medicine (IOM, 2009) guidelines used by providers in the US and many other countries. They're population guidance — your own provider may personalise them.

IOM recommended total gain

Pre-pregnancy BMIOne babyTwins
Underweight (< 18.5)12.7–18.1 kg (28–40 lb)No official range*
Normal (18.5–24.9)11.3–15.9 kg (25–35 lb)16.8–24.5 kg (37–54 lb)
Overweight (25.0–29.9)6.8–11.3 kg (15–25 lb)14.1–22.7 kg (31–50 lb)
Obese (≥ 30.0)5.0–9.1 kg (11–20 lb)11.3–19.1 kg (25–42 lb)

*The IOM published no twin range for underweight — care is individualised; ask your provider.

Where the ranges come from

The targets used here are the Institute of Medicine (IOM, 2009) guidelines — the standard reference for pregnancy weight gain in the US and widely used elsewhere. They start from one insight: the healthy amount to gain depends on where you started, measured by your pre-pregnancy BMI. A lower starting BMI supports a higher gain; a higher starting BMI, a lower one.

How the week-by-week band works

Weight gain isn't linear. A typical first trimester adds only 0.5–2 kg (1–4.5 lb) in total; the steady climb happens in the second and third trimesters. This calculator anchors those two facts and interpolates a healthy band for your exact week, so a week-16 reading isn't judged against a week-40 target.

Reading your result

Within the range means your trajectory matches the guideline band — carry on. Below or above is a conversation starter, not a verdict: fluid shifts, morning sickness, multiple pregnancies and pre-existing conditions all move the number, and one weigh-in matters far less than the trend across weeks. Save results to your history and the trend builds itself.

Twins

Expecting two changes the arithmetic — the IOM's provisional twin ranges are substantially higher and appear automatically when you tick the twins box. For underweight mothers of twins no official range exists, so the calculator says so rather than inventing one.

What weight gain is made of

At term, a typical 13 kg gain is mostly not fat: roughly 3.5 kg of baby, 1.5 kg of placenta and amniotic fluid, 1 kg of uterus and breast tissue, 1.5 kg of blood, 1.5–2 kg of extra fluid — with about 3–4 kg of maternal energy stores for breastfeeding.

ListCalc health tools are educational estimates, not medical advice. Dates and ranges here are population averages — your midwife, OB-GYN or doctor confirms what applies to you. See our disclaimer.

Frequently asked questions

Do I really need to gain weight in the first trimester?
Barely \u2014 typical guidance is just 0.5\u20132 kg (1\u20134.5 lb) across the whole first trimester, and losing a little to morning sickness is common. The meaningful gain happens from the second trimester on.
The calculator says I'm above the range. Should I diet?
No \u2014 weight-loss dieting isn't recommended during pregnancy. An above-range reading is a prompt to review the trend with your provider, who may adjust targets or simply reassure you.
\u201cEating for two\u201d \u2014 how much extra food is it really?
Far less than the phrase suggests: roughly no extra calories in the first trimester, ~340 extra per day in the second and ~450 in the third for a singleton pregnancy \u2014 about a sandwich, not a second dinner.
Which weight do I use as \u2018pre-pregnancy\u2019?
Your usual weight just before conceiving. If you don't know it, use your weight at your first prenatal visit if it was early, or your best honest estimate \u2014 the ranges are wide enough to absorb small errors.
Are the twin ranges as reliable as the singleton ones?
They're published as \u2018provisional\u2019 \u2014 based on less data \u2014 and there's no official range for underweight mothers of twins. Twin pregnancies are monitored more closely precisely so guidance can be personalised.
Where does the weight actually go?
Mostly baby and support systems: fetus, placenta, amniotic fluid, extra blood and fluid, uterus and breast tissue \u2014 plus a purposeful 3\u20134 kg energy reserve for breastfeeding.

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