ForHosting KIT · Developer Utilities

Pregnancy weight gain calculator

A 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 guidelines.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

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 full-term total recommended gain for a singleton pregnancy, the second- and third-trimester weekly rate band, and a cumulative recommended range interpolated to the week you supply. Weeks above forty-two are rejected with invalid_input so post-term outliers never invent 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 pregnancy weight gain calculator need?

Pre-pregnancy BMI (kg/m²) and completed weeks of gestation (0–42). The tool classifies BMI and returns IOM 2009 singleton recommended ranges.

What happens if weeks are greater than 42?

The API returns invalid_input. Gestation above 42 weeks is outside the supported schedule for this calculator.

Which guideline table is used?

Institute of Medicine / National Research Council 2009 singleton pregnancy total and second/third-trimester weekly weight-gain ranges by pre-pregnancy BMI category.

Does this cover twin or multiple pregnancies?

No. pregnancy_type is always singleton. Twin and higher-order schedules use different published ranges and are out of scope.

Is the pregnancy weight gain calculator free?

The browser tool is free and runs locally. API calls use prepaid KIT 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

POSThttps://api.kit.forhosting.com/health/pregnancy-weight-gain

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/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/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/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/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/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.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

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`min_bmi`	10
`max_bmi`	60
`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.

Read the full KIT documentation →

Run — free