DateTime.IsLeapYear() Method in C#

The DateTime.IsLeapYear() method in C# is used to determine whether a specified year is a leap year. This static method returns true if the year is a leap year, and false otherwise. A leap year occurs every 4 years, with exceptions for century years that are not divisible by 400.

Syntax

Following is the syntax −

public static bool IsLeapYear(int year);

Parameters

• year − An integer representing the year to be checked. The year must be between 1 and 9999.

Return Value

Returns a bool value −

• true if the specified year is a leap year

• false if the specified year is not a leap year

How It Works

A leap year follows these rules −

• Divisible by 4 AND not divisible by 100, OR

• Divisible by 400

Using IsLeapYear() with Regular Years

Example

using System;

public class Demo {
    public static void Main() {
        int year = 2019;
        Console.WriteLine("Year = " + year);
        if (DateTime.IsLeapYear(year)) {
            Console.WriteLine("Leap Year!");
        } else {
            Console.WriteLine("Not a Leap Year!");
        }
        
        // Test multiple years
        int[] testYears = {2020, 2021, 2024};
        foreach(int testYear in testYears) {
            Console.WriteLine($"{testYear}: {(DateTime.IsLeapYear(testYear) ? "Leap" : "Not Leap")} Year");
        }
    }
}

The output of the above code is −

Year = 2019
Not a Leap Year!
2020: Leap Year
2021: Not Leap Year
2024: Leap Year

Using IsLeapYear() with Century Years

Example

using System;

public class Demo {
    public static void Main() {
        // Century years - special leap year rules
        int[] centuryYears = {1900, 2000, 2100, 2400};
        
        foreach(int year in centuryYears) {
            bool isLeap = DateTime.IsLeapYear(year);
            Console.WriteLine($"{year}: {(isLeap ? "Leap" : "Not Leap")} Year");
        }
    }
}

The output of the above code is −

1900: Not Leap Year
2000: Leap Year
2100: Not Leap Year
2400: Leap Year

Handling Out of Range Years

The method throws an ArgumentOutOfRangeException if the year is outside the valid range (1 to 9999) −

Example

using System;

public class Demo {
    public static void Main() {
        try {
            int year = 101910;
            Console.WriteLine("Year = " + year);
            bool result = DateTime.IsLeapYear(year);
            Console.WriteLine(result ? "Leap Year!" : "Not a Leap Year!");
        }
        catch (ArgumentOutOfRangeException ex) {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

The output of the above code is −

Year = 101910
Error: Year must be between 1 and 9999.
Parameter name: year

Conclusion

The DateTime.IsLeapYear() method provides a simple way to determine if a year is a leap year, handling all the complex rules automatically. It accepts years between 1 and 9999 and throws an exception for invalid ranges, making it reliable for date calculations and validations.