Ease-In vs Ease-Out: Key Differences Explained

Discover the differences between ease-in vs ease-out, and learn how these timing functions enhance UI/UX and animation in web design.

Have you ever wondered how smooth, engaging animations can keep a user hooked on a website? Understanding the nuances between “ease-in” and “ease-out” in CSS transitions is essential for mastering UI/UX design.

When delving into animation easing functions, you’re navigating a delicate dance of motion design that enhances user experience.

In web development, CSS transitions and JavaScript animations aren’t just about movement—they’re about guiding the user through an interactive journey.

This article aims to decode the intricacies of “ease-in vs ease-out,” shedding light on how animation timing functions and keyframe animations create seamless visual experiences.

By the end, you’ll grasp how to craft polished, responsive animations that not only look professional but also boost web performance.

Expect to dive deep into BĂ©zier curvesbrowser rendering, and the subtle art of pacing your digital motion ease. Ready to transform your front-end development skills? Let’s get started.

Basic Concepts of CSS Timing Functions

The art of web design thrives on the delicate dance of animations. These animations offer a flair that makes our digital creations come alive.

Central to this choreography are CSS timing functions – the unsung heroes behind smooth transitions and engaging user interactions.

Default Transition Timing Function

When we talk about default transition timing in CSS, the conversation inevitably circles back to the ‘ease’ function.

This is the vanilla state, the first stop in our journey through the realm of animation easing.

The ‘ease’ function in CSS

In the simplest terms, ‘ease’ is the default timing function in CSS. It’s like that dependable friend who offers a balanced and harmonious rhythm to your transitions.

What it does is quite magical – it starts off slow, picks up the pace, and then decelerates again before halting. This creates a seamless, natural feel to movement.

Cubic-bezier representation of ‘ease’

Digging deeper, we uncover the cubic-bezier representation, a sophisticated mathematical model that paints the ‘ease’ function.

Imagine a curve that epitomizes smooth acceleration and deceleration. The cubic-bezier function encapsulates this with four control points:

transition-timing-function: cubic-bezier(0.25, 0.1, 0.25, 1);

Dev abstraction aside, this little snippet whispers the secret language of motion, giving our animations life.

Key Timing Functions

Every masterpiece has its specifics. Likewise, our toolkit includes key timing functions: ease-in and ease-out, each adding its unique flavor to transitions.

ease-in: definition and characteristics

Ease-in is the crescendo builder in our animation symphony. It starts with a slow tempo and gains momentum as it progresses.

The acceleration feels natural, like a car smoothly pulling away from a stop.

Characteristics include:

  • Slow start
  • Increased pace towards the end
  • Perfect for elements entering the screen gracefully

In action:

transition-timing-function: ease-in;

Visual magic when you want to initiate engagement.

ease-out: definition and characteristics

The ease-out function, in contrast, is about winding down the rhythm – perfect for exits. It starts briskly and slows down, making it feel like an object is gently landing.

Characteristics are:

  • Quick start
  • Smooth, slow finish
  • Ideal for elements making a gentle exit

It looks something like this:

transition-tiling-function: ease-out;

Utilize it when you want users to notice something fading away softly.

ease: combination of ease-in and ease-out

This brings us to ease, a harmonious blend of ease-in and ease-out. It starts gently, accelerates through the middle, and decelerates at the end.

This multifunctional timing delivers a holistic and balanced feel.


  • Gradual start and end
  • Swift, balanced middle
  • Versatile for various transitions

CSS snippet:

transition-timing-function: ease;

Achieving a natural flow is key, and ease achieves just that, making it a go-to for numerous scenarios.

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Ease-in and Ease-out: Detailed Explanation

Easing functions are the unsung heroes in the drama of web animations.

The subtle differences between ease-in and ease-out make a world of difference in how elements move across the visual landscape.


It’s all about the elegant beginnings.

Description of ease-in function

Ease-in eases you into the animation, like pulling out from a driveway – slow at first, gaining speed as it goes.

It’s the maestro of building anticipation, creating a crescendo in the first half of the motion.

Example syntax in CSS

A sprinkle of CSS to get that glide:

transition-timing-function: ease-in;

It’s like setting the stage for something grand to enter.

Typical use cases and scenarios

Ideal for:

  • Animating elements entering the viewport
  • Highlighting key components
  • Creating suspense before a big reveal

Think of it as the curtain rising in a theater, every pixel builds up the excitement.


Now imagine the graceful exit.

Description of ease-out function

Ease-out is your go-to for exits. It starts quickly, then slows down, easing the viewer into a clean finish, like softly landing a plane.

Example syntax in CSS

Your CSS would look like this:

transition-timing-function: ease-out;

Picture it: elements gracefully winding down their motion, leaving a lasting impression.

Typical use cases and scenarios

Perfect for:

  • Elements fading out or exiting the screen
  • Completing user actions smoothly
  • Ending animations on a softer note

This is the ultimate tool for handling farewells gracefully in your UX design.

Ease-in-out vs Ease

Enter the hybrid maestro.

Differences between ease-in-out and ease

Ease-in-out merges both worlds – starting slow, speeding up, then slowing down again. It’s a balanced routine, like a well-rehearsed dance.

In contrast, ease itself has a more uniform flow but follows a similar principle. However, it often lacks the distinctive mid-point peak of its cousin.

Visual representation and examples

CSS snippet for both:

/* Ease-in-out */
transition-timing-function: ease-in-out;
/* Ease */
transition-timing-function: ease;

Visually, ease-in-out creates a more dynamic flow, perfect for elements that enter, interact, and then exit in one smooth motion.

It’s the A-lister for content sliders and carousel transitions.

Practical Applications and Best Practices

Crafting the perfect animation isn’t just about aesthetics. It’s about the experience.

The kind that makes users feel a seamless connection between themselves and the interface.

Best Practices for Using Ease Functions

Getting it just right starts here.

Matching easing functions to brand aesthetics

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Every brand has a personality. Reflecting it through animations can make a big difference.

For instance, a tech startup might use sharp, quick transitions to give an edgy feel, while a luxury brand prefers smooth, elegant easing functions.

Match the mood:

  • Tech-savvy, fast-paced: Quick ease-out for immediate feedback
  • Luxurious, smooth: Glide-in with ease-in
  • Friendly, approachable: Balanced ease-in-out

Animations communicate more than you think.

Adhering to animation timing guidelines

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Timing is everything. Imagine an animation that lingers too long; it becomes a hurdle, not a feature.

Keep it snappy, ideally between 200-500ms. Long enough to be noticed, short enough to keep momentum.


  • 200-300ms: For most micro-interactions
  • 500ms: For more complex sequences like modal pop-ups

Too long and users get frustrated; too short and they miss the finesse.

Common Use Cases in Web Development

Animations breathe life into static interfaces. Here’s where it gets tangible.

Applying ease-in for entering elements

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When something enters the viewport, it should do so with grace. An ease-in function, starting slow and picking up speed, provides this elegance.

Scenario: A notification slide-in

CSS magic:

.notification {
  transition: transform 0.3s ease-in;
  transform: translateX(-100%);
.notification-show {
  transform: translateX(0);

Use ease-in to make elements feel like they’re naturally introducing themselves.

Applying ease-out for exiting elements

Exits should be as graceful as arrivals. Ease-out is like the bow at the end of a performance, slowing things down, giving users time to process.

Scenario: Modal window fade-out

CSS simplicity:

.modal {
  transition: opacity 0.4s ease-out;
  opacity: 1;
.modal-hide {
  opacity: 0;

Subtle, yet powerful, ease-out allows elements to exit as though they’re fading into the distance.

Example scenarios with CSS code snippets

Let’s marry the theory with practice.

Example: Button hovering effect

.button {
  transition: background-color 0.2s ease;
.button:hover {
  background-color: #ff6347;

Here ease provides a balanced hover effect, offering feedback without being too aggressive. It’s the sweet spot between ease-in vs ease-out principles.

Example: Smooth scrolling

html {
  scroll-behavior: smooth;
  scroll-timing-function: ease-in-out;

This elegance often goes unnoticed, but it’s there, enhancing user experience by making page navigation smoother.

Understanding Easing in Animation and Development

Easing – the subtle powerhouse that breathes humanity into motion. Both animators and developers wield this tool, yet each crafts its magic differently.

Animation Perspective

First, journey back to a time when animations were meticulously hand-drawn, frame-by-frame. The era of Walt Disney.

Historical context: Disney’s 12 Basic Principles of Animation

Everything starts with Disney’s holy grail – the 12 Basic Principles of Animation. These principles are the Bible for animators, dictating how objects should move to appear realistic and appealing.

Among these, two principles stand out to us: slow-in and slow-out.

Slow-in and slow-out principles

These principles form the essence of easing. Picture a pendulum. It doesn’t just start and stop abruptly; it gradually accelerates and decelerates.

This slow-in, slow-out creates lifelike motion.

When it comes to keyframe animations, this is what makes a character jump, not just magically float. A car speeding up, then stopping gracefully at a red light – it all draws back to slow-in and slow-out.

Development Perspective

Now, let’s pull the thread to web development. Here, easing takes on a new form.

The challenge lies in mingling deterministic code with the fluid, often unpredictable nature of user interactions.

Differences in interpretation between animation and web development

Developers don’t work with pencil and paper. Instead, they code. Ease-inease-out, and custom cubic-bezier functions all come into play.

These terms are akin to an animator’s sketch – directives to ensure smooth transitions.

But, unlike an animator who controls every frame, developers often play with events set by user inputs. You can’t predict every click, hover, or scroll.

Explanation of inferred subjects in animations vs development

In animations, the subject is explicit. A character, a car, a bouncing ball. Every motion detail is scripted.

However, on the web, subjects are often inferred. This means, a button’s hover state or a modal’s entry/exit isn’t always explicitly detailed but inferred through CSS and JavaScript.

Here’s where easing functions like ease-in and ease-out come alive.

They control the pacing of inferred subjects, ensuring what feels unscripted becomes a scripted, fluid experience.

Blurring lines: When applying easing functions like ease-in or ease-out to a web animation, think of it as drawing a curve not just through time but through user expectation. A seamless synthesis where code meets artistry.

Advanced Techniques and Customization

Easing functions are the unsung heroes in the cadence of web design. But beyond the basics lies a world of advanced techniques where you can truly make your animations sing.

Custom Easing Functions

The magic begins with customization. While default easing functions like ease-in and ease-out are handy, sometimes you need a touch more… personality.

Creating custom cubic-bezier functions

Think of cubic-bezier functions like drawing a path on a roller coaster.

You control the steep climbs and the gentle slopes. The syntax is just a set of four values defining two points.

Here’s how we can start:

transition-timing-function: cubic-bezier(.42,0,.58,1);

This is the classic ease-in-out curve. But let’s tweak it. Imagine a bounce:

transition-timing-function: cubic-bezier(.68, -0.55, .27, 1.55);

Can you see it? The subtle bounce towards the end? That’s the cubic-bezier magic.

Examples of custom easing functions

Custom functions aren’t just quirky; they’re practical.

  • For a snappy interruption: *
transition-timing-function: cubic-bezier(.4, .0, .2, 1);
  • For a luxurious glide: *
transition-timing-function: cubic-bezier(.25, .1, .25, 1);

Each curve’s distinctiveness turns a simple transition into an experience. Think ASAP sharpness vs end-of-day relaxation.

Combining Easing Functions with Other CSS Properties

Here’s where CSS becomes an art form. Mixing easing functions with other properties brings dynamism to your designs.

Transition timing with transforms

Transforms do more than just move things. When paired with easing functions, they create fluid, captivating sequences.

Imagine a rotating div:

transform: rotate(360deg);
transition: transform 2s cubic-bezier(.42,0,.58,1);

And voilà! Your element doesn’t just rotate; it pirouettes with finesse.

Synchronizing easing with multiple CSS animations

Layering multiple animations with synced easing functions can be mesmerizing.

Consider a button that grows while changing color:

.element {
  transition: transform 0.5s ease-in, background-color 0.5s ease-out;
  transform: scale(1.2);
  background-color: #FF6347;

The dual transition is where the magic happens. Ease-in for the growth, ease-out for the color shift. Different timings give an element that holistic cohesive feel.

Crafting these layered, synchronized transitions makes every interaction feel carefully designed.

FAQ On Ease-In vs Ease-Out

What is the difference between ease-in and ease-out?

Ease-in starts slowly, accelerating towards the end of the animation. It’s like pressing the gas pedal gently. Ease-out begins quickly and decelerates towards the end.

Think of easing into a smooth stop. These timing functions create visually pleasing CSS transitions in UI/UX design.

When should I use ease-in?

Use ease-in when you want an element to start moving smoothly from a still position. This is particularly effective for creating keyframe animations where the initial motion is subtle and then gains speed, guiding the user’s attention toward the final action.

When should I use ease-out?

Ease-out is perfect for finishing actions smoothly. Employ it when animating elements that should come to a gentle halt. This makes the end of a transition feel more natural and user-friendly, crucial for crafting responsive digital motion ease.

How do ease-in and ease-out impact user experience?

They profoundly affect user experience by making animations more intuitive. Proper use of these timing functions enriches motion design and ensures transitions are not jarring, improving overall user engagement.

This nuanced control over animation speed enhances web performance.

Are ease-in and ease-out available in all browsers?

Yes, most modern browsers support these CSS animation properties. However, always check the compatibility of animation timing functions in older versions to ensure a seamless experience across different platforms. This is key in effective front-end development.

How do ease-in and ease-out relate to BĂ©zier curves?

Ease-in and ease-out are predefined BĂ©zier curves in CSS. They control the rate of change for an animation using a curve plotted between points. Understanding these curves allows for more complex, customized animations, optimizing browser rendering.

Can I combine ease-in and ease-out in one animation?

Absolutely. Combining ease-in and ease-out creates the ease-in-out effect, where the animation starts slowly, accelerates in the middle, and decelerates at the end. This produces fluid smooth transition in animation crucial for advanced web development.

What are some practical examples of using ease-in and ease-out?

Ease-in can animate a button expanding when clicked, starting slowly and picking up speed. Ease-out might animate a modal window closing, starting quickly and easing to a stop. These functions are essential for creating refined UI/UX animations.

How does performance in animations benefit from using ease-in and ease-out?

Using these functions optimizes browser rendering by controlling frame rates effectively. This ensures animations run smoothly without causing performance drops. Therefore, animation timing control is vital for maintaining a responsive user interface.

Can ease-in and ease-out be used with JavaScript animations?

Yes, both can be utilized in JavaScript animations. These timing functions can be coded directly within JavaScript, enabling dynamic, programmable control over animations. This is beneficial for complex websites that go beyond basic CSS transitions.


Delving into ease-in vs ease-out unveils the artistry behind creating seamless UI/UX animations. These animation timing functions not only enrich user engagement but also elevate the overall experience.

Understanding their nuances allows you to control animation speed, resulting in smoother, more responsive animations.

Ease-in serves best when initiating movement, offering a gentle start. Meanwhile, ease-out ensures a graceful halt, creating a polished and professional feel for your web development projects. Incorporating both can transform mundane transitions into captivating experiences.

To truly harness the power of ease-in and ease-out, consider:

Mastering these functions enhances not just the aesthetic but also the functional aspects of web design. Implementing these techniques will undoubtedly elevate your work, ensuring fluid, engaging digital interactions.

Ease-In vs Ease-Out: Key Differences Explained

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The Author

Dirk Gavor

Slider Revolution high priest on the mission to find the line between not enough coffee and just a little too much coffee. Same with beer.

For any inquiries or additional resources related to this blog post or else, please don't hesitate to comment below or email me at [email protected].

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