How to prevent announcement bars from causing layout shifts on your website

By Philip Dematis · 10/30/2025 · 3 minutes read

A small thing like an announcement bar can make your whole page jump around. Here’s why that happens, how it impacts user experience and SEO, and how to fix it easily in Shopify or other site builders.

Many websites use announcement bars: Those slim notification strips at the very top that show free shipping offers, discounts, or messages like “New collection out now.”

They seem harmless, but if they aren’t set up properly, they can cause a frustrating experience for visitors and even lower your performance scores on Google.

This happens because of something called Cumulative Layout Shift (CLS). If the announcement bar loads or changes height after the main page has already loaded, it pushes everything else down. That small movement is exactly what Google measures as a layout shift.

Let’s look at what causes this, why it matters, and how to fix it.

What causes layout shift in announcement bars

There are two common situations where announcement bars lead to CLS problems.

1. The bar loads late

If your announcement bar appears after the rest of the page is already visible, it will push all other elements downward.

This often happens when the bar is dismissible - meaning it has a little “x” button that lets the visitor hide it.

Why? Because before showing the bar, the site checks the browser’s local storage to see if the visitor has dismissed it before. That requires a small JavaScript action, which only runs after the main page has already started loading.

So, your visitor sees the header, then suddenly everything drops a few pixels when the bar appears.

2. The bar’s content changes height

Some sites rotate messages in the announcement bar with a slider or carousel. For example:

Slide 1: “Free shipping on orders over $50”
Slide 2: “Buy one, get one 30% off for a limited time”
Slide 3: “New arrivals now live”

If one of those lines is longer and takes up two rows, the height of the bar changes. When that happens, the rest of the page shifts down to adjust, then back up again on the next slide. That constant movement creates layout instability.

Why layout shift is a bigger deal than it seems

Even if it looks like a small detail, layout shift affects both user experience and performance metrics.

Visitors get annoyed. If they’re about to click a button or menu item, and the page moves, it’s easy to misclick or lose focus. This can lead to higher bounce rates.
It hurts your Core Web Vitals score. Google measures CLS as part of page experience metrics. A high CLS score means your page is unstable, and that can lower your SEO rankings.
It impacts ad performance. If you run paid campaigns, Google Ads takes landing page experience into account. A shifting page can reduce your ad quality score and increase your costs.

How to fix announcement bar CLS in Shopify

If your site is built on Shopify, there are simple steps to prevent these issues.

1. Use the theme’s built-in announcement bar

Most modern Shopify themes include a native announcement bar feature. It’s usually designed to load with the rest of the page, so it won’t shift content afterward. Avoid using separate apps for announcement bars - they often add extra JavaScript and load later.

2. Keep consistent text length in sliders

If you use multiple messages, make sure each one takes up roughly the same height. Keep them to one line if possible. That way, when the slides rotate, the height of the bar remains fixed.

3. Pre-allocate space for dynamic elements

If you must use a dismissible bar, make sure the CSS includes a fixed height. That way, even before the JavaScript runs, the browser reserves space for it and avoids shifting other elements.

4. Test on different devices

CLS can appear differently on mobile and desktop. Use Chrome’s Lighthouse tool or PageSpeed Insights to see if your announcement bar causes layout shifts.

FAQ

What is CLS in simple terms? It’s when elements move around while the page loads or updates. Google measures this as part of Core Web Vitals.

How do I check if my site has CLS issues? You can use Google PageSpeed Insights or Chrome DevTools. They’ll highlight which parts of your layout shift during load.

Can animations in announcement bars cause CLS? Yes, especially if the animation changes height or position dynamically without a fixed container.

Wrapping up

A shifting announcement bar might seem like a small issue, but it can have a noticeable impact on how your site feels and performs. Taking a few minutes to stabilize it not only improves visitor experience but can also help with SEO and ad performance.

It’s one of those details that contribute to making the website feel much smoother.