CSS animation-timing-function

The CSS animation-timing-function property allows you to specify how an animation will progress over one cycle of its duration.

More specifically, the property describes how the animation will change speed over the duration of each cycle. This effect is applied by using one of the timing functions described in CSS.

The animation-timing-function is specified using a cubic bézier curve, which is defined by four control points; P₀, P₁, P₂, and P₃. The points P₀ and P₃, which represent the start and end of the animation cycle, are always set to (0,0) and (1,1) repectively.

The animation-timing-function property includes a number of keywords that can be used as a quick way to get a nice transition. Alternatively, you can use the cubic-bezier() function to specify your own cubic-bézier curve.

For a keyframed animation, the animation-timing-function property applies between keyframes, not over the entire animation. For example, in the case of an ease-in-out timing function, an animation will ease in at the start of the keyframe and ease out at the end of the keyframe. A animation-timing-function defined within a keyframe block applies to that keyframe, otherwise the timing function specified for the animation is used.

Syntax

Possible Values

ease

The ease function is equivalent to cubic-bezier(0.25, 0.1, 0.25, 1.0).

linear

The linear function is equivalent to cubic-bezier(0.0, 0.0, 1.0, 1.0).

ease-in

The ease-in function is equivalent to cubic-bezier(0.42, 0, 1.0, 1.0).

ease-out

The ease-out function is equivalent to cubic-bezier(0, 0, 0.58, 1.0).

ease-in-out

The ease-in-out function is equivalent to cubic-bezier(0.42, 0, 0.58, 1.0).

cubic-bezier()

Specifies a cubic Bézier curve. The four values specify points P₁ and P₂ of the curve as (x1, y1, x2, y2). Both x values must be in the range [0, 1], but the y values can exceed that range.

step-start

Represents the timing function steps(1, jump-start) or steps(1, start). This keyword specifies that the animation will jump immediately to the end state and stay in that position until the end of the animation.

step-end

Represents the timing function steps(1, jump-end) or steps(1, end). The animation stays in its initial state until the end, where it directly jumps to its final position.

steps(<integer>[, [ jump-start | jump-end | jump-none | jump-both | start | end ] ]?)

Positive integer representing the amount of equidistant treads composing the stepping function. For example, steps(5, end) indicates that there are 5 treads, with the last one occuring right before the end of the animation. The optional second parameter specifies the jump term (when the jumps occur). If omitted, it defaults to jump-end (or end).

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

initial

Represents the value specified as the property's initial value.

inherit

Represents the computed value of the property on the element's parent.

unset

This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

Cubic Bézier Curves

The ease, ease-in, ease-out, ease-in-out, linear, and cubic-bezier() timing functions use a Bézier curve.

A cubic Bézier curve is defined by four control points, P₀, P₁, P₂, and P₃ as shown in the following diagram.

The P₀ and P₃ control points are always set to (0,0) and (1,1). In other words, they don't move.

However, P₁ and P₂ can be moved with the Bézier curve timing functions. When using the cubic-bezier() function, you can specify the location of these two control points by using an x and y value. Like this: x1, y1, x2, y2. When using one of the keywords, the keyword uses a predefined set of values (as listed above).

Step Timing Functions

The step-end, step-start, and steps() functions are all step timing functions. The way these work is that they progress the animation in steps — as opposed to a smooth curve like the Bézier curve functions.

Here's more detail on how they work.

Using the step-end Keyword

The step-end keyword causes the animation to remain in the start position until the very end. At first, this may appear as though the animation isn't actually working, as the effect won't happen until the end.

Using the step-start Keyword

The step-start keyword causes the animation to jump straight to the end position, then remain there until the end of the animation.

Using the steps() Function

steps(5, end)

This is an example of using steps(5, end).This breaks the animation up into 5 distinct points. The animation waits, then jumps to the next point at the applicable time (which is determined by how many steps you specify).

steps(5, start)

This is an example of using steps(5, start). This is similar to steps(5, end), however, it jumps to the first step immediately instead of waiting for the first time increment.

Basic Property Information

Example Code

Basic CSS

Working Example within an HTML Document

CSS Specifications

• This property is defined in CSS Animations Level 1 (W3C Working Draft)
• The easing functions are defined in CSS Easing Functions Level 1 (W3C Candidate Recommendation)

Browser Support

Browser support for CSS properties can vary, particularly for newer or experimental features. Check current browser compatibility before using a property in production, especially when supporting older browsers.

The following table provided by Caniuse.com shows the level of browser support for this feature.

Initial Value

CSS properties have an initial value that applies when the property has not been explicitly set. The initial value is different from the value inherited from a parent element and may vary between properties.

Inheritance

Some CSS properties inherit their computed value from their parent element by default, while others do not. The inherit, initial, unset, and revert keywords can also be used to control how a property gets its value.

Vendor Prefixes

Most modern CSS properties use the standard, unprefixed syntax. Vendor-prefixed properties such as -webkit- are mainly relevant to older browser versions or specific features and should only be used when required by your browser support targets.