# velocity(value:time:context:) Calculates the velocity of the animation at a specified time. ``` nonisolated func velocity(value: V, time: TimeInterval, context: AnimationContext) -> V? where V : VectorArithmetic ``` ## Parameters `value` The vector to animate towards. `time` The amount of time since the start of the animation. `context` An instance of [`AnimationContext`](/documentation/SwiftUI/AnimationContext) that provides access to state and the animation environment. ## Return Value The current velocity of the animation, or `nil` if the animation has finished. ## Discussion Implement this method to provide the velocity of the animation at a given time. Should subsequent animations merge with the animation, the system preserves continuity of the velocity between animations. The default implementation of this method returns `nil`. > Note: State and environment data is available to this method via the > `context` parameter, but `context` is read-only. This behavior is > different than with ``doc://com.apple.SwiftUI/documentation/SwiftUI/CustomAnimation/animate(value:time:context:)`` and > ``doc://com.apple.SwiftUI/documentation/SwiftUI/CustomAnimation/shouldMerge(previous:value:time:context:)`` where `context` is > an `inout` parameter, letting you change the context including state > data of the animation. For more information about managing state data > in a custom animation, see ``doc://com.apple.SwiftUI/documentation/SwiftUI/AnimationContext``. --- 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)