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Pregnancy Weight Gain Calculator

Recommended weight gain by week, from your starting BMI.

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Before pregnancy

Now

Recommended gain by week

WeekLow endHigh end

The IOM guidelines

Pre-pregnancy BMICategorySingleTwins

Recommended by week

—

Your numbers

Pre-pregnancy BMI—
Total for the pregnancy—
Weekly rate from here—
Gained so far—

—

Against the range for this week

Institute of Medicine guidance, which is population-level advice rather than a personal target. Nausea, medication, oedema and many other ordinary circumstances move people outside the ranges. Discuss anything that concerns you with your midwife or doctor rather than adjusting on your own.

Quick Tool Overview

The Pregnancy Weight Gain Calculator tracks gain against the Institute of Medicine ranges for your pre-pregnancy BMI, week by week rather than as one total. Single and twin pregnancies have separate guidelines, and both are implemented.

What it does
Compares your weight gain to the IOM range for your BMI
You give it
Pre-pregnancy height and weight, current week and weight
You get back
A recommended range for this week and the whole pregnancy
Best for
Reassurance between appointments and antenatal planning
Calculators Free, unlimited use No sign-up Runs in your browser

About the Pregnancy Weight Gain Calculator

See how much weight gain is recommended at your stage of pregnancy, based on your pre-pregnancy BMI and the Institute of Medicine guidelines. The range is given for the week you are in now, not just for the pregnancy as a whole, and twins are handled separately.

The guidelines are deliberately BMI-dependent, because the healthy amount to gain differs substantially: a woman starting underweight is advised to gain 12.5 to 18 kilograms, while one starting in the obese category is advised 5 to 9. Gain is also not linear — the first trimester accounts for only a kilogram or two, with the rest arriving at a fairly steady weekly rate afterwards, which is why a single total figure is far less useful than a weekly range.

Key features of the Pregnancy Weight Gain Calculator

The actual IOM ranges

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.

Week by week, not one total

Gain is not linear — the first trimester accounts for only a kilogram or two — so the range is given for the week you are actually in.

Twin pregnancies included

The separate, higher ranges for twins are implemented rather than left out.

Your position on the range

Current weight is plotted against the recommendation, with the gap in kilograms or pounds.

Points you at a midwife

The page frames the ranges as population guidance worth discussing, not a target to hit alone.

How to use the Pregnancy Weight Gain Calculator

  1. 1

    Enter your pre-pregnancy details

    Height and the weight you started at. Your BMI category sets the recommended range.

  2. 2

    Add your current week

    Either type the week directly or give your due date and let it be worked out.

  3. 3

    Enter your current weight

    Optional, but it plots you against the recommended range for this week.

  4. 4

    Read the range

    Recommended gain so far, the total for the whole pregnancy, and the weekly rate from here.

Frequently asked questions

The IOM guidelines depend on pre-pregnancy BMI: 12.5–18 kg if underweight, 11.5–16 kg if healthy weight, 7–11.5 kg if overweight and 5–9 kg if obese, for a single baby.

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