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Pregnancy Weight Gain Calculator — IOM Ranges by BMI & Week

Pre-pregnancy BMI + week → IOM recommended total gain, the by-week target, and an on-track check — singleton & twins — browser-only

  • Runs locally
  • Category Calculator
  • Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.
Pre-pregnancy BMI
22.0
BMI category
Normal weight
Recommended TOTAL gain (full term)
11.5–16 kg
Recommended gain by week 20
2.9–5.5 kg
Your privacy
Height and weight stay in your browser. Nothing is uploaded — no account, no analytics on the numbers you enter. The shareable link encodes your inputs in the URL, so avoid posting it publicly if the values are sensitive.
Educational use only — based on the US IOM 2009 guidelines. This is NOT a substitute for prenatal care. Your obstetrician or midwife adjusts targets for your individual health, and clinical advice always takes priority.

What this tool does

A pregnancy weight gain calculator built on the US Institute of Medicine (IOM) 2009 guidelines. Enter pre-pregnancy weight and height for the BMI category the recommendation depends on, then your current gestational week to see the recommended total gain for full term and the cumulative gain by that week. Add your current weight and it flags whether you are below, on track, or above the band for now. All four IOM bands are built in — underweight 12.5–18 kg, normal 11.5–16, overweight 7–11.5, obese 5–9 — plus wider provisional twin ranges. The math splits the small first-trimester allowance from the steady weekly rate, so the by-week target tracks how gain really distributes. Metric and imperial, copy summary, shareable link, 100% in-browser. Educational reference, not prenatal care.

Tool details

Input
Numbers
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result + Copy
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
Shareable URL state
Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget
Initial JS <= 9 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Calculator · HR
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Pregnancy Weight Gain Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

  • Getting a realistic range before a purchase, plan, workout, or schedule decision.
  • Comparing scenarios by changing one input at a time.
  • Turning rough assumptions into a number you can discuss.

Calculation checks

  • Double-check units, dates, rates, and rounding assumptions.
  • Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
  • Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

  1. 1 Pregnancy Due Date Calculator Pregnancy due date calculator — track weeks, trimester, baby development by week. Open
  2. 2 BMI Calculator Body Mass Index calculator with WHO + Asian classifications — metric and imperial — browser-only Open
  3. 3 BMR Calculator BMR calculator — basal metabolic rate by Mifflin-St Jeor and Harris-Benedict (compared side-by-side). Open

Real-world use cases

  • Check this week's target between prenatal appointments

    Your last visit was two weeks ago and you want to know if your gain is reasonable before the next one. Enter your pre-pregnancy weight, height, the current week, and today's weight. The by-week band tells you whether you're below, on track, or above for where you are, so you walk into the appointment with a concrete number instead of a vague worry.

  • Plan a target before you start trying

    Knowing your pre-pregnancy BMI category up front sets expectations for total gain. Enter your current weight and height to see which IOM band you fall in (underweight, normal, overweight, obese) and the full-term total it implies, then pair it with the BMI calculator and ideal-weight calculator to plan ahead.

  • Understand the twin numbers

    Twin pregnancies follow different ranges, and the gap is large — a normal-BMI twin pregnancy targets 16.8–24.5 kg versus 11.5–16 kg for a singleton. Tick "Carrying twins" to see the provisional IOM range for your category and a note about why the underweight-twin band is borrowed from the normal range.

  • Convert between metric and imperial for a clinic abroad

    Many clinics report gain in pounds while charts at home are in kilograms. Enter your numbers in whichever unit you measured, switch the toggle, and read the band in the other unit. The shareable link keeps the exact scenario so you can send it to a partner or compare two readings.

  • Share a scenario with a partner or midwife

    Copy the result summary or share the URL so someone else lands on the same BMI, the same total band, and the same by-week target. It makes "is this gain okay?" a shared, specific conversation rather than two people guessing from memory.

Common pitfalls

  • Using your current pregnant weight instead of your pre-pregnancy weight for the BMI. The IOM band is fixed by your starting BMI; feeding in a later weight shifts you into the wrong category and the wrong total range.

  • Reading the full-term total as a target for right now. The big number (e.g. 11.5–16 kg) is for week 40; at week 20 the recommended cumulative gain is much smaller. Use the by-week figure for where you actually are.

  • Applying singleton ranges to a twin pregnancy. Twins need substantially more gain — forgetting the "Carrying twins" toggle makes an on-track twin pregnancy look "above range."

Privacy

Pre-pregnancy weight, height, current week, and current weight stay in your browser while the calculation runs. There is no account and the values are not uploaded to a server. The shareable link encodes your inputs in the URL query string, so avoid posting that link publicly if the numbers are sensitive — copy the text summary instead.

FAQ

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Made by Toolora · 100% client-side · Updated 2026-06-13