# isLess(than:) Returns a Boolean value indicating whether this instance is less than the given value. ``` func isLess(than other: Double) -> Bool ``` ## Parameters `other` The value to compare with this value. ## Return Value `true` if this value is less than `other`; otherwise, `false`. If either this value or `other` is NaN, the result of this method is `false`. ## Discussion This method serves as the basis for the less-than operator (`<`) for floating-point values. Some special cases apply: - Because NaN compares not less than nor greater than any value, this method returns `false` when called on NaN or when NaN is passed as `other`. - `-infinity` compares less than all values except for itself and NaN. - Every value except for NaN and `+infinity` compares less than `+infinity`. The following example shows the behavior of the `isLess(than:)` method with different kinds of values: ``` let x = 15.0 x.isLess(than: 20.0) // true x.isLess(than: .nan) // false Double.nan.isLess(than: x) // false ``` The `isLess(than:)` method implements the less-than predicate defined by the [IEEE 754 specification](http://ieeexplore.ieee.org/servlet/opac?punumber=4610933). --- 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)