A sticky header keeps navigation within reach as people scroll, which sounds purely helpful until you watch it eat a third of a phone screen on every page. Done badly, it hurts both usability and search performance. Here's how to keep the benefit without the cost.
First, shrink on scroll. A header that's tall at the top but compresses once the user starts moving respects screen real estate. Mobile users especially feel the difference when a 90-pixel bar collapses to 50.
Second, hide on scroll-down, reveal on scroll-up. This pattern — sometimes called the "smart header" — gets out of the way while reading and reappears the instant someone reverses direction looking for navigation. It's the closest thing to reading intent that a header can manage.
Third, watch your layout shift. A header that loads, then resizes, then snaps into place damages your Cumulative Layout Shift score, and Core Web Vitals feed directly into ranking. Reserve the space upfront so nothing jumps.
Fourth, keep it light. Heavy sticky headers with background blur and shadow filters can cause repaint jank on lower-end devices. Test scrolling on a mid-range Android, not just your own flagship.
Fifth, ensure it never obscures anchor targets. When someone clicks a jump link, account for the header height so the destination heading isn't hidden underneath. A little scroll-margin in CSS saves a lot of confusion. Small fixes, but together they turn a liability into a genuine convenience.