Yahrzeit Calculator

Accurately determine future Yahrzeit dates for the next 10 years based on the Hebrew calendar.

What is a Yahrzeit Calculator?

A yahrzeit calculator is a specialized tool used by the Jewish community to determine the annual anniversary of a loved one’s passing according to the Hebrew calendar. Unlike the Gregorian calendar, which is based on the solar cycle, the Jewish calendar is lunisolar. This means that a death anniversary (Yahrzeit) falls on a different Gregorian date every year.

Using a yahrzeit calculator is essential for observing Jewish mourning traditions, such as reciting the Kaddish prayer, lighting a 24-hour memorial candle, and visiting the cemetery. These observances are traditionally held on the Hebrew date of the death, which begins at sunset the preceding evening. Our tool helps you navigate these complexities, including leap years (Adar I and Adar II) and the shifting sunset times.

Yahrzeit Calculator Formula and Mathematical Explanation

The mathematics behind a yahrzeit calculator involves converting a Gregorian date to a Julian Day Number, then mapping that number to the complex structure of the Hebrew calendar. The Hebrew calendar consists of 12 or 13 months, with months alternating between 29 and 30 days.

The core logic follows these steps:

1. Sunset Adjustment: If the passing occurred after sunset, the yahrzeit calculator adds one day to the Gregorian date before conversion.
2. Gregorian to Hebrew Conversion: Calculating the Molad (lunar conjunction) and applying the four rules of postponement (Dehiyyot) to determine the start of the year.
3. Anniversary Projection: Locating the same Hebrew month and day in subsequent years, accounting for the 19-year Metonic cycle which dictates leap years.

Hebrew Calendar Variables Table

Variable	Meaning	Unit	Typical Range
H-Month	Hebrew Month	Name	Nisan to Adar (II)
H-Day	Hebrew Day	Integer	1 to 30
Metonic Cycle	Leap Year Position	Year	1 to 19
Sunset Rule	Time adjustment	Boolean	Yes/No

Practical Examples (Real-World Use Cases)

Example 1: A person passed away on March 15, 2020, at 10:00 PM. Since it was after sunset, the yahrzeit calculator treats the Hebrew date as the 20th of Adar, 5780. In 2024 (a leap year), the Yahrzeit falls on March 30 (Adar II), while in 2025, it falls on March 20.

Example 2: A passing occurred on September 10, 2023, at 10:00 AM. The yahrzeit calculator identifies this as the 24th of Elul, 5783. The anniversary in 2024 will be September 27, 2024 (24th of Elul, 5784).

How to Use This Yahrzeit Calculator

1. Select the Date: Use the date picker to choose the Gregorian date of death.
2. Specify Sunset: Indicate if the death happened after sunset. This is the most common mistake made when manually calculating dates.
3. Review Results: The yahrzeit calculator will immediately display the Hebrew date of passing and the next Gregorian anniversary.
4. Examine the Schedule: Review the 10-year table to plan future memorial services and Yizkor dates.
5. Copy and Save: Use the copy button to save the dates to your digital calendar or print them for family members.

Key Factors That Affect Yahrzeit Calculator Results

• The Sunset Boundary: Jewish days begin and end at sunset, not midnight. A yahrzeit calculator must account for this or the anniversary will be off by one day.
• Leap Years (Adar I & II): The Hebrew calendar adds an entire month seven times every 19 years. If someone passes in Adar during a non-leap year, specific rules determine which Adar is used in leap years.
• Month Lengths: Cheshvan and Kislev can have 29 or 30 days depending on the year’s “character” (defective, regular, or complete).
• Rosh Hashanah Postponements: The start of the Hebrew year can be delayed based on the day of the week or the time of the new moon.
• Year of Passing: The very first Yahrzeit might follow different customs if the burial was delayed significantly, though usually, it follows the date of death.
• Local Timezones: Sunset occurs at different times globally. While the yahrzeit calculator uses a general rule, specific halachic questions should be directed to a Rabbi.

Frequently Asked Questions (FAQ)

What happens if someone died on the 30th day of a month?

If the month in the current year only has 29 days, the Yahrzeit is typically observed on the 1st of the following month or the 29th, depending on specific family or congregational traditions. Our yahrzeit calculator follows standard Rabbinical conventions.

Does the Yahrzeit date change every year?

In the Hebrew calendar, the date stays the same (e.g., 10th of Kislev). However, because the Hebrew and Gregorian calendars are not aligned, the Gregorian date changes annually.

When do I light the Yahrzeit candle?

The candle should be lit at sunset on the evening preceding the date provided by the yahrzeit calculator, as that is when the Hebrew day begins.

How do leap years affect Yahrzeits in Adar?

If a death occurs in Adar during a non-leap year, the Yahrzeit is usually observed in Adar II during leap years. Our yahrzeit calculator accounts for these nuances.

Is Yahrzeit calculated from the day of death or burial?

Yahrzeit is strictly calculated from the day of death. However, for the first year of mourning (the 11-month Kaddish period), some traditions look at the burial date.

Can I use this for the Yizkor service?

While Yizkor is recited on specific holidays (Yom Kippur, Shemini Atzeret, Passover, and Shavuot), the yahrzeit calculator is used for the personal anniversary of the death.

What if I don’t know if the death was after sunset?

If the time is unknown, standard practice is to assume it was before sunset unless there is evidence otherwise. Consult a Rabbi for specific guidance.

Is the calculation the same for Sephardic and Ashkenazi traditions?

The calendar math is the same, but certain customs regarding leap years and the 30th day of the month may vary slightly between communities.