# isNaN A Boolean value indicating whether the instance is NaN (“not a number”). ``` var isNaN: Bool { get } ``` ## Discussion Because NaN is not equal to any value, including NaN, use this property instead of the equal-to operator (`==`) or not-equal-to operator (`!=`) to test whether a value is or is not NaN. For example: ``` let x = 0.0 let y = x * .infinity // y is a NaN // Comparing with the equal-to operator never returns 'true' print(x == Double.nan) // Prints "false" print(y == Double.nan) // Prints "false" // Test with the 'isNaN' property instead print(x.isNaN) // Prints "false" print(y.isNaN) // Prints "true" ``` This property is `true` for both quiet and signaling NaNs. --- 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)