ForHosting KIT · Developer Utilities

Conception window calculator

Conception window calculator: enter your values and see a clear result on this page. Free for individual checks; API from $0.002.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

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

How is the conception window calculated?

Ovulation is estimated as last_period plus (cycle_length − 14). The window runs from five days before ovulation through one day after. Next period is last_period plus cycle_length. All dates use civil calendar arithmetic.

Which input fields are required?

Only last_period (YYYY-MM-DD). Aliases lmp, period_start, and last_menstrual_period are accepted. cycle_length is optional and defaults to 28 (range 21–45). Invalid input returns invalid_input and is not billed.

Why is the luteal phase fixed at 14 days?

This tool implements the common textbook calendar model with a fixed 14-day luteal phase. It does not accept a custom luteal length; that keeps the contract simple and fully deterministic for goldens and SEO demos.

Is this a medical diagnosis of fertility?

No. It is an educational calendar estimate for planning and teaching. Irregular cycles, postpartum recovery, and contraception all change real fertility; use clinical tools when medical decisions depend on timing.

What does the conception window calculator cost?

The browser widget is free. API calls use prepaid KIT balance at $0.002 per successful task; invalid input is not 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/conception-window

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/conception-window \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"last_period":"2026-03-01"}'

const res = await fetch("https://api.kit.forhosting.com/health/conception-window", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "last_period": "2026-03-01"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/conception-window",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "last_period": "2026-03-01"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/conception-window", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"last_period":"2026-03-01"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"last_period":"2026-03-01"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/conception-window", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "last_period": "2026-03-01"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.conception_window",
  "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.

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 →