Definition:Calendar/Gregorian/Year

Definition
A Gregorian year, also known as the civil year, is the length of a year as defined using the Gregorian calendar.


 * $1$ Gregorian year $= \begin{cases} 366 \, \text {days} & : 400 \mathrel \backslash y \\

365 \, \text {days} & : 400 \nmid y \text{ and } 100 \mathrel \backslash  y\\ 366 \, \text {days} & : 100 \nmid y \text{ and } 4 \mathrel \backslash  y\\ 365 \, \text {days} & : 4 \nmid y \end{cases}$ where:
 * $y$ denotes the number of the year
 * $4 \mathrel \backslash y$ denotes that $y$ is divisible by $4$
 * $4 \nmid y$ denotes that $y$ is not divisible by $4$.

Also see

 * Discrepancy between Gregorian Year and Tropical Year