When Is Rosh Hashanah and Yom Kippur 2026: Exact Dates, Calendar Mechanics, and Postponement Rules

Rosh Hashanah 2026 begins at sundown on Friday, September 11, and runs through Sunday, September 13. Yom Kippur 2026 begins at sundown on Sunday, September 20, and ends the evening of Monday, September 21. Both dates are fixed by the Hebrew calendar, not by the Gregorian one, so the solar dates shift every year within a defined window. The ten days between them are the Aseret Yemei Teshuvah, the Ten Days of Repentance.

The Hebrew calendar runs on lunar months, not solar years

The Hebrew calendar is lunisolar. Each month begins near a new moon, so twelve lunar months total roughly 354 days. A solar year is about 365.25 days. Left alone, the holidays would drift about 11 days earlier every year and eventually land in summer.

To prevent that drift, the calendar adds a thirteenth month in seven out of every nineteen years. This is the Metonic cycle, a 19-year pattern in which years 3, 6, 8, 11, 14, 17, and 19 are leap years. A leap year in this system runs about 383 to 385 days. The added month is Adar I, inserted before the standard Adar.

Rosh Hashanah falls on the first day of Tishrei, the seventh month in the religious count. Yom Kippur falls on the tenth of Tishrei. Because both holidays sit in the same month, the gap between them is always nine days, plus the day counts at each end. That interval never changes, even though the Gregorian dates do.

The practical upshot: the autumn holidays stay in autumn. The spring holidays stay in spring. The calendar self-corrects instead of drifting. Plainly, the lunar months set the rhythm, and the leap month keeps the seasons in place.

Why the dates shift by up to about a month

Because 19 Hebrew years equal 235 lunar months, which is very close to 19 solar years, the calendar realigns with the sun every 19 years. Within that cycle, Rosh Hashanah can fall anywhere from early September to early October on the Gregorian calendar.

The earliest possible date is September 5, and the latest is October 5. That gives a roughly 30-day spread across the full cycle. The 2026 date of September 11 sits near the early-middle part of that range.

For comparison, here is how the pair of holidays lands in nearby years. The civil dates below are the evening-before starts, which is how Jewish holidays are observed: a day begins at sunset.

The nine-day gap is constant. What moves is the anchor date. Notice that 2027 jumps back to early October after 2026's mid-September start. That back-and-forth is the Metonic cycle doing its job.

The postponement rules that most explainers skip

The calendar does not simply place Rosh Hashanah on the astronomical new moon of Tishrei. A set of postponement rules, called the dechiyot, can push the date forward by one or two days. These rules exist to keep the calendar internally consistent.

There are four postponement conditions. Two are practical and two are mathematical.

The first rule prevents Rosh Hashanah from falling on certain weekdays relative to Yom Kippur. If the new moon of Tishrei lands on a Sunday, Wednesday, or Friday, Rosh Hashanah is pushed to the next day. This is called lo ADU Rosh, an acronym for the Hebrew days aleph (Sunday), daled (Wednesday), and vav (Friday). The reason is to avoid Yom Kippur falling on a Friday or Sunday, which would create back-to-back Sabbath-like restrictions that are hard to observe.

The second rule handles a different edge case: if the new moon falls after midday, the day is treated as already past, and Rosh Hashanah moves forward. Two further rules adjust for the length of the prior year so that the calendar year stays within allowed lengths of 353, 354, or 355 days for common years and 383, 384, or 385 days for leap years.

The counterintuitive detail: the Hebrew calendar is not purely astronomical. It is a fixed arithmetic system with built-in legal adjustments. Two communities can compute the same new moon and still land Rosh Hashanah on different civil dates if their rules diverge at the margins. This is why some calendar apps and printed calendars disagree by a day around edge cases.

For 2026, none of these postponements push the date off the September 11 start. The computed new moon and the postponement checks converge there.

What actually happens across the ten days

The stretch between the two holidays has its own structure. The timeline below shows the sequence of observances most Jews encounter.

Tzom Gedaliah is a minor fast day. It can be postponed to Sunday if the third of Tishrei falls on the Sabbath, which is a separate application of the same "no fast on Sabbath" logic that shapes the major calendar rules. In 2026, September 14 is a Monday, so the fast is observed on its nominal date.

Yom Kippur is a full fast day, roughly 25 hours from sundown to nightfall the next day. The exact length depends on latitude and the time of year. In New York City, the 2026 fast runs from about 6:45 p.m. on September 20 to about 7:55 p.m. on September 21. In more northern cities the window stretches; nearer the equator it shortens. These times are approximate and should be checked against a local Jewish calendar.

Edge cases and common misconceptions

Several myths recur every year. Clearing them up matters for anyone scheduling around the holidays.

The most common error is treating Rosh Hashanah as a single day. It is observed for two days in the Diaspora and, in most Reform and some other communities, one or two days in Israel and elsewhere. The two-day observance is called yom tov sheni shel galuyot, the second festival day of the Diaspora.

A second misconception is that the dates are unpredictable. They are entirely predictable. Anyone can compute them with the arithmetic rules, and they are published decades in advance. What feels unpredictable is only the Gregorian conversion.

A third error: the holidays are not always in September or always in October. As the comparison table shows, they oscillate. For 2026 specifically, both land in September.

A red-flag warning for planners: sunset-based start times mean the civil date is the evening before the named day. If a workplace calendar lists "Rosh Hashanah: September 12," the observance actually begins the evening of September 11. Similarly, Yom Kippur observance begins the evening of September 20 even though the fast day is often listed as September 21.

Another edge case involves travel and the International Date Line. Observance follows local sunset, so a traveler crossing the date line can encounter the holiday start at a different civil clock time. Communities near the line have established local conventions, but the underlying rule is sunset-based, not clock-based.

Practical scheduling steps

For anyone planning events, travel, or work coverage around these dates, the following steps reduce errors.

Confirm the exact start time for your city, not just the date, because candle lighting and fast times depend on local sunset. Block the evening before each holiday, not only the daytime. Rosh Hashanah begins the evening of September 11; Yom Kippur begins the evening of September 20. Treat September 11 through September 21, 2026, as a single sensitive window for major deadlines, since the intervening days carry religious obligations even outside the two named holidays. If you rely on a printed or app calendar, cross-check against a second source for the postponement edge cases. For business travel, note that the fast on Yom Kippur lasts about 25 hours and affects stamina and scheduling the next day.

What the calendar cannot tell you

The arithmetic gives exact civil dates, but several practical details fall outside the calendar's scope. Local candle-lighting and fast times depend on latitude, longitude, and the community's customary calculation. Different streams of Judaism observe slightly different customs around the second day and around the minor fast.

The 2026 dates are stable and well established. What varies is how they are observed, not when they fall. Anyone with medical conditions that affect fasting, or with travel plans that cross the date line, should consult both a local religious authority and a qualified medical professional rather than relying on the date arithmetic alone.

This article is general educational information about calendar mechanics, not a religious ruling or a medical or legal opinion. It does not provide guidance on fasting safety or personal observance. For decisions about fasting, health, or observance, consult a qualified local professional or your own religious authority.