ForHosting KIT · Developer Utilities

Calendar method safe days calculator

The calendar method safe days calculator applies the Standard Days Method to a single cycle length and returns the lower and higher fertility calendar days of the cycle, plus the safer early and late day ranges.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Day one is the first day of menstrual bleeding. The fertile window is fixed at cycle days eight through nineteen inclusive—twelve consecutive higher-fertility days used by CycleBeads-style teaching and many natural-family-planning primers. Safer early days run from one through seven; safer late days run from twenty through the end of the cycle. Classic efficacy studies for the Standard Days Method assume regular cycles between twenty-six and thirty-two days; this endpoint still computes the same window for other lengths in a practical twenty-one to forty-five day range and flags eligible false when the length falls outside that band. The browser widget and the API share one pure deterministic module, so homework demos, wellness apps, and automation pipelines never disagree on day numbers. This is educational fertility-awareness arithmetic, not medical advice and not a guarantee against pregnancy.

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 do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

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/safe-days-calendar

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/safe-days-calendar \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"cycle_length":28}'

const res = await fetch("https://api.kit.forhosting.com/health/safe-days-calendar", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "cycle_length": 28
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/safe-days-calendar",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "cycle_length": 28
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/safe-days-calendar", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"cycle_length":28}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"cycle_length":28}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/safe-days-calendar", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "cycle_length": 28
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.safe_days_calendar",
  "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 →