Rosh Hashanah date calculator
Enter a year and get the civil date of Rosh Hashanah: in 2026, 1 Tishri falls on 12 September and opens Hebrew year 5787. The date comes from the fixed arithmetic Hebrew calendar, so you can plan years ahead. 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
- Date
- 2026-09-12
- Month
- 9
- Day
- 12
- Hebrew year
- 5,787
Rosh Hashanah, the Jewish New Year, begins at 1 Tishri and does not fall on a fixed Gregorian day: it moves through September and October according to the arithmetic Hebrew calendar. Planners, schools, synagogues, and product calendars need a repeatable civil date for each year without maintaining hand-edited almanacs. This capability accepts a single Gregorian year, maps it to the corresponding Hebrew year (Anno Mundi equals Gregorian year plus 3761), applies the traditional molad of Tishri and dehiyyot postponement rules in pure integer arithmetic, and returns the proleptic Gregorian civil date of 1 Tishri as an ISO-8601 string plus component fields.
What the arithmetic Hebrew calendar computes for 1 Tishri
The fixed arithmetic Hebrew calendar is a lunisolar system: months track mean lunar conjunctions (moladot), while leap months keep the year aligned with the seasons over a nineteen-year Metonic cycle of two hundred thirty-five months. Rosh Hashanah is the civil and liturgical start of the year on 1 Tishri.
Its date is not taken from a live astronomical observation of the new moon; it is computed from the mean molad of Tishri for that Hebrew year, then adjusted by the classical postponement rules (dehiyyot) so that the year length stays in the allowed common or leap ranges and so that 1 Tishri does not fall on Sunday, Wednesday, or Friday.
Those constraints are the same family of rules documented in standard calendrical references such as Dershowitz and Reingold: count months elapsed since the calendar epoch, convert the molad into a day count, apply the first postponement class in the elapsed-days formula, then add a zero-, one-, or two-day year-length delay when needed. The result is a fixed day number that this capability converts into a proleptic Gregorian year, month, and day with pure integer math.
Where Rosh Hashanah dates fit into real scheduling work
Jewish communal life, many school districts, university religious-observance policies, and some employers treat Rosh Hashanah as a day when services, leave, and event schedules must not conflict. Product calendars, HR systems, logistics cut-offs, and content pipelines therefore need a reliable 1 Tishri civil date for every year they plan, not only the current autumn.
Feed this capability a range of years in a loop or through a batch wrapper, store the ISO dates, and derive related observances with simple day offsets when your product also tracks Yom Kippur (ten days later on 10 Tishri) or the intermediate days of the High Holiday season. Keep requests small, pin the ISO strings in tests, and you get reproducible High Holiday anchors for LMS plugins, edge workers, and published community calendars.
What you can do with it
Multi-year High Holiday calendar tables
Compute 1 Tishri for each year in a planning horizon, then derive related observances and blackout dates for school, HR, and community event systems.
Synagogue and community event planning
Publish service times and seating plans that depend on Rosh Hashanah without maintaining hand-edited almanacs for each autumn.
FAQ
Which calendar rules are used?
The fixed arithmetic Hebrew calendar: molad of Tishri for Hebrew year (Gregorian year + 3761), classical dehiyyot postponements, and a pure Rata Die conversion to the proleptic Gregorian civil date of 1 Tishri.
Is the date the evening start or the daytime of 1 Tishri?
The civil Gregorian date of daytime 1 Tishri (ISO calendar day).
What years are accepted?
Any integer year greater than or equal to 1.
Which Hebrew year starts on Rosh Hashanah?
The Hebrew year equals the Gregorian year plus 3761. For 2026 that gives 5787, so the Rosh Hashanah that falls on 12 September 2026 opens the year 5787.
Why does Rosh Hashanah never fall on a Sunday, Wednesday or Friday?
The classical postponement rules move 1 Tishri by one or two days when needed, so it never lands on those weekdays and the length of the year stays within the allowed range.
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/rosh-hashanah \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"year":2026}'const res = await fetch("https://api.kit.forhosting.com/date/rosh-hashanah", {
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/rosh-hashanah",
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/rosh-hashanah", 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/rosh-hashanah", 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.rosh_hashanah",
"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.
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
Invalid years fail with invalid_input instead of inventing a date.
Input contract, response shape, and how to read the result
The year is the Gregorian civil year in which Rosh Hashanah falls in the Northern Hemisphere autumn (September or October). The response does not include sunset, candle-lighting, or time-zone offsets: Jewish day boundaries begin at local sunset, so liturgy and community schedules may still need local sunset data on top of this civil date. POST a JSON body with one required field, year, as a positive integer greater than or equal to one. Missing year, empty strings, non-finite values, non-integers, and years below one fail with invalid_input and are not billed. On success the body includes date as a full ISO calendar string YYYY-MM-DD for the daytime of 1 Tishri; year, month, and day as integers matching that civil date; and hebrew_year as the Anno Mundi year (Gregorian year plus 3761) whose Tishri new year was computed. There is no optional Julian switch and no multi-day range: this endpoint is dedicated to the first day civil date so product and SEO intent stay clear. Pricing is a flat $0.002 per successful request under the published item unit. Use the free in-browser tool for one-off checks, and the API when you need the same contract inside a batch job, a school calendar, or a multi-year holiday generator that must match published almanacs year after year.
Where Rosh Hashanah dates fit into real scheduling work
That determinism is especially useful when an audit asks how a holiday table was produced: the algorithm family, the Gregorian year, the Hebrew year, and the ISO result are enough to reproduce the answer from first principles without reconstructing historical moon observations or depending on a third-party calendar API that might change or rate-limit.
Integration use cases
Product and content holiday pipelines
Anchor seasonal content, promotions, and support staffing to the correct Rosh Hashanah weekend across years with a deterministic API contract.
Technical questions
How do I get the Rosh Hashanah date for a year?
Call the capability with { "year": 2026 } (or any integer year ≥ 1). The response includes date as an ISO string such as 2026-09-12 plus month, day, and hebrew_year fields.
What does the Rosh Hashanah date API cost?
The browser tool is free for interactive use. The API charges the published base price of $0.002 per successful request from your prepaid balance; invalid input is not charged.