# nan A quiet NaN (“not a number”). ``` static var nan: Double { get } ``` ## Discussion A NaN compares not equal, not greater than, and not less than every value, including itself. Passing a NaN to an operation generally results in NaN. ``` let x = 1.21 // x > Double.nan == false // x < Double.nan == false // x == Double.nan == false ``` Because a NaN always compares not equal to itself, to test whether a floating-point value is NaN, use its `isNaN` property instead of the equal-to operator (`==`). In the following example, `y` is NaN. ``` let y = x + Double.nan print(y == Double.nan) // Prints "false" print(y.isNaN) // Prints "true" ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)