Friday the 13th finder
Enter a year and see every Friday the 13th in it: 2026 has three, on 13 February, 13 March and 13 November. All twelve months are checked, so you get the full list and the count at once. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Year
- 2,026
- Quantity
- 3
- Dates
- 2026-02-13, 2026-03-13, 2026-11-13
- Fridays
- 2026-02-13, 2026-03-13, 2026-11-13
Enter an integer Gregorian year and this tool returns the full list of ISO dates, a count, month names, and step-by-step notes for each of the twelve day-thirteen checks.
What Friday the 13th means on a Gregorian calendar
Friday the thirteenth is simply the calendar coincidence that day number thirteen of a month falls on weekday Friday. Whether that day is a Friday depends only on the weekday of the first of that month, which in turn depends on the year’s leap status and the fixed month lengths after February.
A common year and a leap year shift the later months differently because the leap day sits after February thirteenth: January and February weekdays match between a leap year and the common year that would otherwise align with it only until the leap day, then March onward diverges. That is why two consecutive years almost never share the same Friday-the-thirteenth months, and why a year can have one, two, or three such dates—never zero in some configurations and never more than three under the standard Gregorian month table.
This tool does not assign meaning or luck; it only reports the mathematical fact.
Practical tips, limits, and related searches
Keep years inside the published range so four-digit Gregorian practice and sibling date tools stay consistent. Round-trip checks are easy: pick one returned ISO date and confirm with a weekday calculator that it is Friday, and confirm that months not listed have a thirteenth on another weekday.
This landing targets people searching for a Friday the 13th finder, Friday the thirteenth dates in a year, or unlucky Friday calendar online; it is not a day-of-week calculator for arbitrary dates, not a business-day counter, and not a leap-year checker by itself—though it does report the leap flag used during the scan. Prefer this capability when you already have a year and only need the list of Friday-the-thirteenth dates; if you have a full YYYY-MM-DD string and need its weekday, use the day of the week calculator instead.
Year bounds stop at nine thousand nine hundred ninety-nine to keep the product surface aligned with other pure-parse date capabilities in this catalog.
What you can do with it
Trivia and content calendars
Editors and social teams list every Friday the 13th in the upcoming year when planning posts, event pages, or themed promotions without opening a wall calendar.
Classroom weekday drills
Teachers assign a year and ask students to find Friday the 13ths by hand, then compare against a deterministic list and step log.
FAQ
How many Friday the 13ths can a year have?
Under the Gregorian calendar a year has one, two, or three Friday the 13ths depending on the weekday of January 1 and whether the year is a leap year. This tool always scans all twelve months and returns the exact count.
What happens if the year is not an integer?
Floats, empty strings, and non-numeric values are rejected so a silent empty list cannot hide bad input.
Does this use my computer’s clock or timezone?
No. Weekdays are computed with pure integer Zeller arithmetic for day 13 of each month. Results do not depend on Date, timezone, or wall-clock time.
What format are the dates returned in?
ISO calendar form YYYY-MM-DD with day always 13, for example 2026-02-13. The entries array also includes month number and English month name.
Is the Friday the 13th finder free?
The browser tool is free and runs locally.
Related tools
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/date/friday-13th \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"year":2026}'const res = await fetch("https://api.kit.forhosting.com/date/friday-13th", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"year": 2026
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/date/friday-13th",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"year": 2026
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/date/friday-13th", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"year":2026}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"year":2026}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/date/friday-13th", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"year": 2026
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "date.friday_13th",
"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
year_min | 1 |
year_max | 9999 |
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. |
Technical notes
A Friday the 13th finder answers a calendar curiosity people search every year: given a year, which months have a Friday the thirteenth? Non-integer years are rejected with a clear invalid_input error instead of a silent empty list.
What Friday the 13th means on a Gregorian calendar
In the proleptic Gregorian calendar used here, every month has a thirteenth, so there are always twelve candidates to test in a year: January thirteen through December thirteen.
How to call the API and what comes back
The value must be a whole number in the inclusive range from one through nine thousand nine hundred ninety-nine; decimal fractions, scientific notation strings, empty strings, and non-numeric types are rejected. Prefer sending a numeric year rather than a pre-formatted string when you control the client; string years are accepted only when they match a strict integer pattern without a decimal point. Send a JSON body with one required integer field named year, which may also be supplied under the aliases y or value. On success the response echoes year as an integer, sets count to the number of Friday-the-thirteenth dates found, sets dates and fridays to the same ordered array of ISO strings in YYYY-MM-DD form with day always thirteen, sets entries to objects with month number, English month name, and iso, sets is_leap_year to the Gregorian leap flag for that year, and includes message as a short English summary plus steps as an ordered array that records the leap check and each month’s include-or-skip decision. Failed validation—missing field, non-integer number, non-numeric string, or year outside the published range—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related searches
When teaching or testing, keep a small known set: a year with three Friday the thirteenths, a year with one or two, a leap year, and a deliberate non-integer failure such as a float year to prove the invalid_input path. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send bad years.
Integration use cases
Test fixtures for calendar UIs
Engineering teams freeze known years with one, two, or three Friday the 13ths for highlight badges and notification schedulers without using Date.