Various websites provide Jewish calendars, including Chabad.org and Hebcal. To find the calendar on Chabad.org, hover over Jewish Practice and click Jewish Calendar. Hebcal lists Jewish calendar options, including holiday dates and a date converter, on its homepage.
The calendar on Chabad.org lists major Jewish holidays along with other smaller events and information, such as daily study, candle lighting times and Torah readings. The site also offers other features at the side of the page, such as a date converter, birthday date calculator and Bar Mitzvah date calculator.
Hebcal provides a listing of major holidays and a calendar customization feature. It also provides a date converter and calculators for important dates. It prominently includes a calculator for Shabbat times, as these vary depending on the local length of day; Jewish hours are calculated by dividing daylight time by 12.
The Jewish calendar follows the cycles of the moon as well as the sun. Jewish months follow the lunar cycle of 29.5 days, making the Jewish year 354 days long. This causes the Jewish calendar to shift 11 days a year compared to the modern Gregorian calendar, which is purely solar and has 365 days in a year. An extra month is added to the Jewish year every two or three years to keep holidays properly aligned with the seasons.