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Pregnancy Weight Gain Calculator

View IOM pregnancy weight-gain reference ranges by BMI category and pregnancy week.

By Nitin Raturi · Last reviewed

Your details

How to use this Pregnancy Weight Gain Calculator

Use your pre-pregnancy measurements to see how IOM reference ranges relate to a completed pregnancy week.

  1. Enter your height and pre-pregnancy weight.
  2. Choose singleton or twin pregnancy and enter a completed week.
  3. Optionally add a current weight to compare the estimated gain range.
  4. Read the full-pregnancy range, trimester rates, and week-specific estimate together.
  5. Discuss your own care and any questions with your clinician.

Good to know

  • The ⓘ beside each field explains its role and accepted range.
  • For weeks before 14, the week view is an even interpolation of the source’s first-trimester total, not a weekly clinical target.
  • Use clinician guidance for your own circumstances, including if it differs from this general reference.

Height

Your height is used with your pre-pregnancy weight to calculate BMI.

How to fill it in

  • Enter a height in centimetres from 120 to 220.
  • Use the height you normally provide to your clinician.

Example

At the default inputs, the calculated BMI is 22.0.

Keep in mind: BMI is a screening measure and does not describe every person’s health or pregnancy needs.

Pre-pregnancy weight

This is the weight from before pregnancy used to place the estimate in a BMI category.

How to fill it in

  • Enter kilograms from 30 to 250.
  • If you do not know this weight, avoid treating a guess as a precise category.

Example

With the default inputs, the week 20 estimate is 2.95–5.50 kg.

Keep in mind: The resulting category selects a population-level reference; your clinician may interpret it differently for you.

Pregnancy type

The 2009 IOM report gives different reference ranges for singleton and twin pregnancies.

How to fill it in

  • Choose singleton or twins.
  • The report does not establish a twin range for the underweight BMI category.

Example

For the default singleton example, the weekly rate range is 0.35–0.50 kg.

Keep in mind: This calculator does not cover higher-order multiple pregnancies or individual medical factors.

Completed pregnancy week

Enter the number of full weeks completed, from 1 through 42.

How to fill it in

  • Use a whole week, not a day count or a decimal.
  • Weeks 1–13 use an explicitly labelled interpolation because the source gives only a first-trimester total.

Example

At the default week 20, the estimated cumulative gain range is 2.95–5.50 kg.

Keep in mind: The estimate is not a week-by-week clinical target; the first-trimester display is a simple interpolation.

Current weight (optional)

An optional current weight lets the calculator compare your reported gain with the week-specific reference estimate.

How to fill it in

  • Enter kilograms from 30 to 300, or leave this blank.
  • The comparison is current weight minus pre-pregnancy weight.

Example

The default example has a current gain of 3.00 kg, compared with 2.95–5.50 kg.

Keep in mind: A comparison outside the estimate is not a diagnosis or a reason to change care without your clinician.

Reference ranges

BMI 22.0 · Normal BMI category · Singleton · completed week 20

Total pregnancy gain range

11.50–16.00 kg

Full-pregnancy reference range in the IOM table.

Gain range for week 20

2.95–5.50 kg

Calculated from the first-trimester range plus the weekly rate for later weeks.

First-trimester gain

0.50–2.00 kg

Total gain range for the first trimester in the IOM guidance.

Weekly rate, second and third trimesters

0.35–0.50 kg/week

Reference rate range, not a personal prescription.

General information only; this is not medical advice, diagnosis or treatment. Talk to a qualified healthcare professional about your situation and follow your clinician’s guidance.

These ranges use standard BMI categories. Some Asian populations may experience health risks at lower BMI levels; WHO’s consultation discussed additional public-health action points, not pregnancy-specific IOM categories. Ask your clinician how BMI applies to you. WHO expert consultation report.

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

The IOM reference combines a total-pregnancy range with separate trimester guidance; the week view is an estimate, not a personal target.

  1. Step 1Calculate pre-pregnancy BMI22.04using height and pre-pregnancy weight
  2. Step 2Select the matching tableNormal BMI categorywith a singleton or twin pregnancy option
  3. Step 3Estimate cumulative gain2.95 kg to 5.5 kgusing completed week and trimester rates

BMI is weight in kilograms divided by height in metres squared. The calculator uses standard BMI categories from the IOM guidance and does not alter them for a particular population.

Reading the ranges

At the default inputs, the IOM table gives 11.5 kg to 16 kg as the full-pregnancy range.

Default example: 60 kg pre-pregnancy weight and week 20
BMI
pre-pregnancy kg ÷ (height in metres)²
After week 13
first-trimester range + completed weeks after week 13 × weekly rate range
Optional comparison
current weight − pre-pregnancy weight
  • BMIbody mass index used to select a table group 22.04
  • wcompleted gestational week 20
  • rweekly rate range after week 13 0.35 kg/week–0.5 kg/week
  1. Full-pregnancy IOM rangetable for BMI group and pregnancy type11.5 kg–16 kg
  2. First-trimester rangeIOM total for the first trimester0.5 kg–2 kg
  3. Estimated gain by week 20first-trimester range plus 7 weeks at the published rate2.95 kg–5.5 kg

The total-pregnancy range and rate-based week estimate come from related but distinct parts of the report. They are not forced to meet at one exact point. Display values are rounded; calculations retain full precision.

The first trimester is different

  • Source gives a totalIOM gives a 0.5–2 kg first-trimester range, not a week-by-week schedule.
  • Early week displayFor weeks 1–12, this tool divides that total evenly as a visual estimate only.
  • Individual careReal patterns vary; this display is not a clinical target or an assessment.

BMI and population context

Standard BMI groups are used here to match the IOM tables; they may not capture every population's health context.

A WHO expert consultation described variation in health risk among Asian populations below BMI 25 and discussed additional public-health action points at BMI 23 and 27.5. Those points are not pregnancy-specific IOM categories. They do not replace individual clinical interpretation. See the

WHO consultation report

and discuss how BMI applies to you with your clinician.

These ranges start from your BMI before pregnancy. Dates and BMI can be checked in their own tools.

To find your pre-pregnancy category, use the BMI calculator, which also shows the lower cut-offs suggested for Asian populations. The pregnancy conception calculator estimates conception and the fertile window from a last period or due date.

For daily protein in pregnancy, the protein intake calculator follows ICMR-NIN 2020 guidance for Indian adults.

Common mistakes

  • Mistake: Treating the week estimate as a personal goal.

    Instead: Use it as general context and follow your clinician’s advice.

  • Mistake: Reading the first-trimester interpolation as an official weekly rule.

    Instead: The IOM source gives a trimester total; the early-week values are evenly interpolated for display.

  • Mistake: Comparing weights from different units or dates.

    Instead: Enter kilograms and use a current weight measured around the week you selected.

  • Mistake: Assuming a twin reference exists for every BMI group.

    Instead: The report does not establish a twin range for the underweight group.

Assumptions and limits

  • Source rangesThe IOM tables provide population-level reference values.
  • No personal assessmentThe tool does not consider pregnancy complications or individual clinical context.
  • Transparent interpolationThe early-week display evenly divides the source’s trimester total.

The optional comparison subtracts pre-pregnancy weight from current weight. The calculator does not assess fetal growth, fluid changes, complications, nutrition, or health conditions. It does not advise changing care or treatment.

Sources and methodology

Weight-gain categories, full-pregnancy ranges, first-trimester total and later weekly rates come from the National Academies report

Weight Gain During Pregnancy: Reexamining the Guidelines

(2009), Tables 5-1 and 5-2 for singleton and twin total ranges, and Table 5-3 for trimester and weekly rates. The Asian-population caveat is based on the WHO Expert Consultation report linked above. Sources checked on 22 Oct 2026.

This tool was prepared by Nitin Raturi, a software engineer, and has not been medically reviewed. Last reviewed: 22 Oct 2026. See the project methodology and changelog in the page details.

This tool is for general information and is not medical advice, diagnosis or treatment. Talk to a qualified healthcare professional about your situation.

A separate script recomputes every test range two ways, and a third time in the report’s pound figures. Read how we test our calculators, or browse more health calculators.

Frequently asked questions

Which pregnancy weight-gain guidance does this calculator use?

It uses the US National Academies / IOM 2009 ranges for singleton and twin pregnancies, grouped by pre-pregnancy BMI.

How is the BMI category calculated?

BMI is pre-pregnancy weight in kilograms divided by height in metres squared. Standard cut-offs select the reference category used in the IOM report.

What does the first-trimester range mean?

The IOM report gives a total first-trimester range of 0.5 to 2 kg. For a week before week 13, this calculator shows a linear display interpolation, not an IOM weekly target.

How does the week-specific range work after week 13?

It adds the relevant IOM weekly rate range to the first-trimester range for each completed week after week 13.

Can I use it for twins?

Yes, it shows the report’s twin-pregnancy ranges for normal, overweight and obesity BMI categories. The report does not establish a twin range for underweight BMI.

Does the optional weight check tell me whether my pregnancy is healthy?

No. It compares entered weight gain with a broad reference estimate only; it does not diagnose or assess pregnancy health.

What about Asian BMI thresholds?

Some Asian populations may have health risks at lower BMI levels, but the WHO action points are not pregnancy-specific IOM cut-offs. Discuss how BMI applies to you with your clinician.

Should I follow this range instead of my clinician’s advice?

No. This is general information. Follow your clinician’s advice for your own circumstances, including if it differs from this reference.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 22 Oct 2026; next review due by . Found an error? Tell us.

Changelog

  • : Registered at the owner's request. Built from IOM 2009 reference ranges, first-trimester interpolation disclosure, and optional weight comparison.

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