Hebrew Year Length Calculator

Because both leap months and calendar postponement rules affect the result, a year can have one of six valid lengths: 353, 354, or 355 days in a common year, and 383, 384, or 385 days in a leap year. The result also labels the year deficient, regular, or complete and reports whether it is a leap year, making the output convenient for calendar software, research, scheduling, and data validation.

Why Hebrew years have six possible lengths

The Hebrew calendar is lunisolar: its months follow lunar cycles while its leap-year pattern keeps festivals in their intended seasons. A common year contains twelve months, and a leap year adds a thirteenth month. That distinction creates two broad ranges, but it does not determine the final total by itself. The lengths of Cheshvan and Kislev can vary, producing deficient, regular, and complete forms. A deficient common year has 353 days, a regular common year has 354, and a complete common year has 355. Their leap-year counterparts have 383, 384, and 385 days. This calculator resolves all of those rules from the Hebrew year number alone. Its response includes the original year, the exact day count, a classification, and a leap-year flag. That compact structure is useful when a program needs a reliable value rather than a formatted calendar or a conversion tied to a civil date. No location, clock, or contemporary calendar service is needed.

How the deterministic calculation works

The calculation first counts the lunar months elapsed before Tishri of the requested year using the fixed nineteen-year Metonic cycle. It then computes the traditional molad parts and applies the Hebrew calendar postponement arithmetic to obtain an integer day number for Rosh Hashanah. The same operation is performed for the following Hebrew year, and subtracting the two day numbers gives the requested year length. This is more dependable than assembling a list of month lengths from an assumed year type, because the year type is precisely what must be discovered. Every operation is bounded integer multiplication, division, remainder, comparison, or subtraction. The implementation does not call JavaScript Date, inspect a machine timezone, read the current time, use randomness, or contact a network service. Consequently, the same input produces the same JSON result in UTC and in every other runtime timezone. The accepted range is deliberately finite so all intermediate integers remain safely exact in JavaScript number arithmetic.

Reading and using the result

Send the Hebrew year as an integer, for example 5784, rather than a Gregorian year or a text label. The days field is the full span from Rosh Hashanah of that year to Rosh Hashanah of the next. The leap field tells you whether the result belongs to the twelve-month common group or the thirteen-month leap group. The classification field describes the variable shape: deficient means one day below the group’s regular length, regular means the middle length, and complete means one day above it. This terminology lets downstream systems reason about Cheshvan and Kislev without guessing from the total. Calendar generators can select month tables, import pipelines can reject inconsistent records, and educational tools can demonstrate cycle behavior. Treat the Hebrew year number as its own calendar coordinate; do not infer it by merely adding a constant to a Gregorian year near January, because Hebrew years begin in Tishri and overlap parts of two Gregorian years. API requests are priced at $0.002.