Twin pregnancy weight gain calculator
A twin pregnancy weight gain calculator turns pre-pregnancy body mass index and completed weeks of gestation into the recommended weight-gain range clinicians and educators cite from the Institute of Medicine twin guidelines.
Run — free
Enter BMI in kilograms per square metre and gestational weeks from zero through forty-two; the tool classifies the BMI band as underweight, normal weight, overweight, or obese, returns the twin-term total recommended gain, the second- and third-trimester weekly rate band, and a cumulative recommended range in kilograms interpolated to the week you supply. Twin totals are substantially higher than singleton tables and are aligned to about thirty-seven weeks, when many twin pregnancies reach term. BMI that is missing, zero, negative, or not a finite number is rejected with invalid_input so a nonsense index never invents a schedule. Prenatal education, midwifery worksheets, patient-facing apps, and coding kata fixtures all need that same deterministic table lookup without a spreadsheet. The path is pure arithmetic and fixed tables—no network, no random seeds, no wall-clock dependence—so the free browser runner and the prepaid API return the same JSON after fixed decimal rounding every time you call it.
How to use it
Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.
Check your inputs
Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.
Use it again or automate it
Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.
What you can do with it
Get an answer now
Enter one set of values and see the result without building a spreadsheet or script.
Compare scenarios
Change one value at a time and rerun the calculation to understand what affects the result.
Automate repeated work
Use the API when the same calculation needs to run inside your product or workflow.
FAQ
What inputs does the twin pregnancy weight gain calculator need?
Pre-pregnancy BMI (kg/m²) as a positive number and completed weeks of gestation (0–42). The tool classifies BMI and returns IOM 2009 twin recommended ranges in kilograms.
What happens if BMI is not a positive number?
The API returns invalid_input. Zero, negative, missing, or non-numeric BMI is outside the contract and is never charged.
Which guideline table is used?
Institute of Medicine / National Research Council 2009 provisional twin pregnancy total-gain ranges by pre-pregnancy BMI, with weekly rates interpolated so week 37 matches those totals. Underweight uses the commonly cited 22.7–28.1 kg provisional band.
Is this the same as a singleton pregnancy weight-gain calculator?
No. pregnancy_type is always twin. Singleton schedules use lower totals and a forty-week horizon; this calculator is the twin table aligned to about thirty-seven weeks.
Is the twin pregnancy weight gain calculator free?
The browser tool is free and runs locally. API calls use prepaid balance at $0.002 per successful request; failed tasks are never charged.
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/twin-pregnancy-weight-gain \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"bmi":22,"weeks":20}'const res = await fetch("https://api.kit.forhosting.com/health/twin-pregnancy-weight-gain", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"bmi": 22,
"weeks": 20
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/twin-pregnancy-weight-gain",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"bmi": 22,
"weeks": 20
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/twin-pregnancy-weight-gain", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"bmi":22,"weeks":20}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"bmi":22,"weeks":20}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/twin-pregnancy-weight-gain", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"bmi": 22,
"weeks": 20
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.twin_pregnancy_weight_gain",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_weeks | 42 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |