301 vs 302: what actually changes

The difference in one line each

Google documents the two behaviours separately, and the distinction is about canonicalisation rather than about whether the browser arrives in the right place. Both kinds of redirect send the visitor to the destination.

• Permanent (301, 308): the redirect target is shown in search results, and the indexing pipeline uses the redirect as a signal that the target should be canonical.
• Temporary (302, 303, 307): the source page is shown in search results, and the redirect is not used as a canonical signal.

Why the wrong one is so easy to ship

Most frameworks, hosting platforms and CDNs default to a temporary redirect when you do not specify. A redirect added quickly — during a migration, or to retire a page — therefore tends to be temporary by accident rather than by decision.

The visitor experience is identical, so nothing looks wrong. What happens instead is that the old URL stays in the index and the new one struggles to replace it.

About the "you lose 15% through a redirect" figure

This number circulates widely. It does not appear in Google’s redirect documentation, which describes the canonicalisation behaviour above and does not state a loss percentage.

We are not going to tell you the true figure, because we do not know it and neither does anyone outside Google. The honest position is that the documented, observable difference between 301 and 302 is which URL gets indexed — and that is reason enough to use the right one.

What to check

For each redirect on your site, ask one question: will the original URL ever serve content again? If not, it is a permanent move and should return 301. Genuinely temporary situations — maintenance pages, split tests, geographic routing — should stay 302.

One caution: permanent redirects are cached aggressively by browsers, so reversing one later is slow to take effect for people who have already followed it. Only mark a redirect permanent when the move genuinely is.