Mobile conversion killers are the small-screen problems that make a visitor give up: buttons pushed below the fold, pop-ups that cannot be closed, forms that open the wrong keyboard, tap targets that are too small, and pages that load slowly on a phone connection. Each one looks minor on desktop. On a phone, each one can end a sale. The fix is to walk your buying path on a narrow phone width, as a stranger, and remove every obstacle you meet.
Why does mobile need its own check?
Most store owners and founders build and review their sites on a laptop. Their customers often arrive on a phone, from social media, an ad, or a text from a friend. That mismatch means the version of the site that earns money is often the version nobody on the team looks at.
Phones also make every existing friction bigger. A long form is tiring on desktop and exhausting on a phone. A vague button is a small pause on desktop and a lost tap on mobile. A slow page is annoying on office Wi-Fi and a reason to leave on a train.
What are the most common mobile conversion killers?
The main button is below the fold
On desktop, the hero, the product image, the price, and the buy button may all fit on one screen. On a phone, the hero image alone can fill the screen. The visitor has to scroll before they even learn what to do. Many will not.
Pop-ups that cover everything
A discount pop-up that appears instantly, fills the screen, and has a tiny close button is a common reason mobile visitors bounce. Google's Search documentation explains its guidance on intrusive interstitials and dialogs: developers.google.com/search/docs/appearance/avoid-intrusive-interstitials.
Forms that fight the thumb
- Email fields that do not open the email keyboard.
- Phone fields that open the full keyboard instead of the number pad.
- Autocorrect changing names and addresses.
- Labels that disappear once you start typing, so the visitor forgets what the field was for.
- Error messages that appear above the fold while the visitor is typing below it.
Tap targets that are too small or too close
Links squeezed together in a footer, tiny size selectors, and close buttons in the corner all lead to mis-taps. A mis-tap that opens the wrong page feels like the site is broken.
Sticky elements that eat the screen
A sticky header, a cookie banner, a chat bubble, and a promotional bar can together cover a large share of a small screen. Each was added for a good reason. Together, they leave little room for the product.
Slow pages on real connections
Heavy images, autoplay video, and many third-party scripts slow mobile pages. Google's guide to Core Web Vitals, at web.dev/articles/vitals, explains the loading, interactivity, and visual stability measures that matter for user experience.
Horizontal scrolling and cut-off content
A table, an image, or a long word that is wider than the screen makes the whole page wobble sideways. Visitors read that as a broken site.
How do I find mobile problems on my own site?
- Open your site on a phone, or in your browser's device mode at a narrow width.
- Start signed out, from the page where most visitors arrive, not from the homepage you designed first.
- Try to complete the money path: buy a product, start a trial, or book a call.
- Note every scroll you did not expect, every tap that missed, every field that was awkward.
- Repeat at a larger phone width, and once in landscape if your audience uses it.
Do it with your thumb, not a mouse. The thumb is how your customers experience the site.
What should I fix first?
Fix what blocks the money path before what makes it prettier.
- First, anything broken: a button that does nothing, a form that will not submit, a page that will not load.
- Second, anything that hides the next step: a buy button below the fold, a pop-up that covers the page.
- Third, anything that slows the visitor: extra fields, the wrong keyboard, tiny tap targets.
- Last, visual polish.
After each fix, walk the path again on the same width. Mobile layouts have a habit of fixing one thing and breaking another.
How does this apply to AI-built apps?
If you built your product with Lovable, Bolt, Cursor, or Base44, the generated layout often looks great in the preview pane on a laptop. The preview is not the phone. Generated components can overflow, stack in odd orders, or hide navigation behind a menu that does not open. It is worth testing the mobile path before every launch, not after the first complaint.
Persqo can run your journey at a phone width with realistic AI visitors. Each visitor tries to complete a goal, and you get mobile screenshots, a replay of the session, and a list of where they got stuck. If you built with an AI tool, you also get a fix prompt for Claude Code or Cursor. Start with a free check, or see the builders page for testing an app built with AI.
For the checkout specifically, use the checkout friction audit. For forms, read the guide to form friction.
The mobile conversion checklist
- The primary action is visible on the first screen at a narrow phone width.
- Pop-ups wait, and close with an obvious, thumb-sized button.
- Email, phone, and number fields open the right keyboard.
- Labels stay visible while typing.
- Error messages appear next to the field that caused them.
- Tap targets are large enough and spaced apart.
- Sticky bars and banners leave room for the content.
- No horizontal scrolling anywhere on the money path.
- Pages load acceptably on a mobile connection.
- The full path was completed, end to end, on a phone width, after the latest change.
Questions people ask
Why do mobile visitors convert worse than desktop visitors?
Phones make every friction bigger. Screens are small, typing is slow, connections can be unreliable, and visitors are often distracted. A page that is merely busy on desktop can become unusable on a phone.
Is a responsive theme enough?
A responsive theme makes the layout fit the screen. It does not guarantee that the important parts stay visible, that forms use the right keyboard, or that pop-ups can be closed. You still need to walk the buying path on a real phone width.
Which phone sizes should I test?
Start with a common narrow phone width and a common larger phone width. Most layout problems show up at the narrow end. You do not need to own many devices to catch the problems that matter most.
Do pop-ups hurt mobile conversion?
Pop-ups that cover the content on arrival frustrate mobile visitors and can be hard to close on a small screen. Google also documents guidance against intrusive interstitials on mobile. If you use them, make them easy to dismiss and delay them until the visitor has seen the page.