Inertial bounce and overshoot in After Effects

What is the inertial bounce expression in After Effects?

It is a short expression, written by Dan Ebberts, that adds a realistic-looking bounce back to keyframed motion. It appears in his bounce-and-overshoot article on motionscript.com, a site that describes itself as "Dan Ebberts' AE Expressions and Scripting Resource". The article page carries the line "Copyright © 2012 Dan Ebberts".

The name causes confusion. People search for it as inertial bounce, but when we checked the motionscript.com pages on 3 November 2026 that phrase was not used there. The article calls it Keyframe Bounce Back. Look for that heading when you want the original. Copies passed around elsewhere may have been edited, so treat the article as the reference text.

It is expression code, not a plugin or a script you install. You paste text onto a property; there is no file to install. Our page on plugins, scripts and extensions in After Effects explains the three kinds of file and where each one goes.

The article pages we read don't publish a licence or terms for reusing the code, or which After Effects versions it has been tested in. We don't reproduce the full expression here either. Copy it from the article, where it is credited and complete.

How do I add the bounce expression to a layer?

Keyframe the move first, then paste Dan Ebberts' expression onto that same property and preview. The order matters: the expression is built around keyframes, as its name, Keyframe Bounce Back, says.

1. Keyframe the move. On the property that should bounce, set a start value and the value the layer should land on.
2. Open the article. Go to the Keyframe Bounce Back section of Dan Ebberts' bounce-and-overshoot article on motionscript.com (linked in the sources below).
3. Copy all of it. Select from the first line, e = .7; g = 5000; nMax = 9;, down to the last line. A partial copy breaks the expression.
4. Add an expression to the keyframed property and paste. If you haven't done this before, our guide to adding expressions in After Effects walks through it.
5. Preview. Play through the last keyframe and watch the landing.
6. Tune e and g at the top of the expression until the bounce feels right. The next section covers this.

Each property that should bounce needs its own keyframes and its own copy of the expression. The bounce is worked out from your keyframes, so you can retime them later without pasting the expression again.

For more ready-made code, see our After Effects expressions library. The wiggle and loopOut guides cover the two expressions most editors learn next.

How do I change the elasticity and gravity of the bounce?

Edit the two numbers at the top of the expression. The article says you control the bounce by adjusting the elasticity (e) and gravity (g) variables. The defaults on the first line are e = .7 and g = 5000.

Both values sit on that first line, so you don't need to read the rest of the code to tune the bounce. This method stops you going round in circles:

1. Change one value at a time. Leave g at 5000 and try a few values of e. Then fix e and move g.
2. Preview the same few frames each time. Set a short work area around the landing so each preview is quick.
3. Write down the pairs you like. A note such as "logo drop: e .5, g 6000" saves you guessing on the next job.
4. Change only the numbers. Keep the line written as in the article, with its decimal points and semicolons in place.

The same line also sets nMax = 9. The article text we checked names only e and g as the bounce controls. Leave nMax as it is unless you have read what it does in the full article.

Reusing your tuned version. Once you have a pair you like, save the whole expression with your values in a text file next to your project templates. You can also put it on a one-click button. We cover that, using mouzerun, in our own section further down.

How is an overshoot different from a bounce in After Effects?

An overshoot passes its target value and settles back onto it. A bounce comes back off a hard stop, like a ball off a floor. The article's address on motionscript.com, bounce-and-overshoot, names both. The bounce-back expression is the one this page is about.

Pick by what the object is:

• Overshoot suits things that spring into place: a title scaling past 100% and easing back, a card sliding a little past its spot, a needle swinging past a reading.
• Bounce suits things that hit something: a logo dropping onto a line, an icon landing on the bottom of the frame.

How to key an overshoot by hand

You don't need an expression for a single overshoot. Four keyframes do it:

1. Keyframe the start value.
2. A few frames before the end, keyframe a value past the target. For a scale-up to 100%, that might be 110%.
3. Keyframe a smaller miss on the other side, for example 97%.
4. Keyframe the target, 100%.

Then smooth the keyframes so the motion doesn't look stepped. Our Easy Ease guide covers that step. Hand keys are easy to retime and need no code, but each overshoot is built once. Change the target and you rebuild the in-between keys. The expression avoids that because it works from your keyframes.

A third route is a ready-made easing curve. Our page on After Effects easing presets covers Easing lab's 44 ready curves and six curve types, Bounce and Elastic among them. Easing lab is in the After Effects workspace, which is Windows only.

Why is my bounce expression not working?

Most failures come from a partial paste, a property with no keyframes or a typo in the values. Work through these in order:

1. Was the whole expression copied? Compare the first and last lines of your paste with the article.
2. Does the property have keyframes? The expression is built around keyframes. With nothing keyframed, there is no move for it to bounce back from.
3. Is it on the keyframed property? If one property is keyframed but the expression sits on another, nothing visible happens at the landing.
4. Did the first line change? A deleted semicolon or a stray character in e = .7; g = 5000; nMax = 9; can stop the expression. Retype only the numbers.
5. Are you previewing past the last keyframe? The bounce comes after the move lands. If your work area ends on the last keyframe, you won't see it.
6. Is it a copy from somewhere else? Copies may have been edited. Replace yours with the text from motionscript.com and test again.

Supported After Effects versions are not published on the article. If it still fails, try the original text in a new comp with one keyframed layer. That tells you whether the problem is the expression or something else on your layer.

Which bounce method should you use?

Use the expression when you want a bounce that follows your keyframes as you retime them. Use keyframes, by hand or from a tool, when you want to edit every frame or hand the comp to someone who doesn't edit code. Checked on 3 November 2026. We make mouzeclick, one of the options below.

One question decides most cases: will the timing change after you add the bounce? If yes, keep it as an expression until the edit is locked, then bake it if you need to.

Should you bake a bounce expression to keyframes?

Bake it when the animation is final, or when the comp goes to someone who shouldn't touch code. Keep it live while the timing is still moving.

A live expression works from your keyframes. Move the landing keyframe three frames later and the bounce moves with it. The cost is that the bounce itself isn't visible as keys, so you can't nudge one frame of it. You also depend on the expression text staying intact when the project is opened elsewhere.

Baked keyframes are the opposite. Each frame of the bounce is a key you can drag, delete or copy to another layer. Change the main move, though, and the old bounce keys no longer match it. You either re-bake or fix them by hand.

A sensible order for client work:

1. Build the move and add the expression.
2. Tune e and g while the edit is still changing.
3. Lock the timing with the client.
4. Bake, then trim or adjust individual bounce keys if needed.

Newton skips the expression stage. Its product page says it "only creates keyframes".

Is there an inertial bounce script or plugin for After Effects?

On the pages we checked, Dan Ebberts' bounce is expression text, not a script. If you would rather use a tool than paste code, one option is Newton 4, a physics tool for After Effects sold on aescripts.com. Its product page states "Newton only creates keyframes", so it is not an expression tool: you get editable keys, not live code.

What its page shows, checked on 3 November 2026:

• Version: 4.0.77 is listed as the current version, dated 30 January 2024.
• After Effects: 2024, 2023, 2022, 2021 and 2020 are listed. Later versions are not listed.
• Systems: Windows and macOS, with native support on Apple Silicon (M1 and above). macOS 10.14 Mojave is the minimum.
• Demo: limited only by a 25-frame export restriction.
• Price: the text we read does not give the price of a new Newton 4 licence. Newton3 owners who bought after 1 September 2023 upgrade free; otherwise the upgrade is $99.99. Newton2 owners upgrade for $150. There is no upgrade discount for Newton1. Floating licences cost extra.

Where Newton is the better pick: when you want physics-based motion written as plain keyframes, with no expression code left in the project, and you work in one of the listed After Effects versions. The 25-frame demo lets you test that before you pay. For one layer landing on one line, the free expression is often enough.

Where mouzeclick fits (we make it)

This section is about our own product. mouzeclick doesn't replace Dan Ebberts' expression, but it can cut down the copying, pasting and baking around it. These are the parts that touch this job:

• mouzeexpr (Windows and Mac) applies 24 ready expressions with settings, in five groups. You can Apply, Update or Remove one, or Bake it to keyframes. For the expressions it applies, that covers the "lock the timing, then bake" step without hand-keying. See every item on the mouzeexpr feature page.
• mouzerun (Windows and Mac) makes your own one-click buttons. A button can hold a script, an expression, an animation preset, a menu command or a keyframe ease. Paste your tuned bounce expression into a button, with your own e and g values, and apply it in one click. Buttons can be exported and imported. Details are on the mouzerun page.
• mouzekit (Windows and Mac) has 28 After Effects tools in 7 groups, Rigs among them. Each tool is one undo step, and its expressions work in any language of After Effects. See the mouzekit tool list.
• Easing lab, in the After Effects workspace, has six curve types: Bezier, Spline, Elastic, Bounce, Wave and Steps. It comes with 44 ready curves and offers Read, Apply and Auto. You can copy a curve as an expression or export curves as .mzgraph. The same workspace's Library holds 25 recommended expressions.

Platforms: the 22 extensions, mouzeexpr, mouzerun and mouzekit among them, run on Windows and Mac. The workspaces, which include Easing lab and the Library, are part of mouzeclick on Windows only. The Mac app does not include them. Mac setup takes four steps, covered on our Mac install page.

The mouse app runs on both systems. Its After Effects Tool wheel puts 114 tools in 13 groups a flick away, and an Options wheel slot can hold typed text, keys or a macro.

Where mouzeclick is not the pick: if you only need one bounce now and then, Dan Ebberts' free expression does the job. If you want physics-based motion written as keyframes, that is what Newton is made for.

The trial runs 3 days, no card, and every After Effects tool works fully. Plans are in the pricing section.

Questions people ask

Sources

Checked on 2026-11-03. Prices and features change: each link goes to the maker's own page.

1. Dan Ebberts, bounce and overshoot article (motionscript.com)
2. motionscript.com: Dan Ebberts' AE Expressions and Scripting Resource
3. Newton 4 product page (aescripts)

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