1,284. Which Months Are Malei and Which Are Chaseir

Hilchos Kiddush HaChodesh 8:5

Following is the schedule of the malei and chaseir months based on our current, fixed calendar: Tishrei is always malei; Teves is always chaseir. From Teves on, months alternate malei and chaseir. The result is: Tevet - chaseir; Shvat - malei; Adar - chaseir; Nisan - malei; Iyar- chaseir; Sivan - malei; Tamuz - chaseir; Av - malei; Elul - chaseir. In a leap year, Adar I is malei and Adar II is chaseir.

Hilchos Kiddush HaChodesh 8:6

Regarding Marcheshvan and Kislev, sometimes they are malei, sometimes they are chaseir, and sometimes Marcheshvan is chaseir while Kislev is malei. If both of these months are malei, it is called a year whose months are complete. If both these months are chaseir, it is called a year whose months are deficient. If Marcheshvan is chaseir and Kislev is malei, it is called a year whose months are in order.