How long do SSDs actually last?

For normal use, considerably longer than most people fear, and typically longer than you will keep the machine. The concern comes from the fact that flash memory cells wear with each write, which is true but is usually the wrong thing to worry about.

Manufacturers rate drives in total bytes written, and consumer drives are commonly rated for hundreds of terabytes. Ordinary use, meaning documents, photos, software and browsing, writes a small fraction of that annually. At typical rates the rated endurance corresponds to decades rather than years, and drives frequently exceed their rating substantially in endurance testing.

The activities that genuinely consume endurance are sustained heavy writing: video editing with large scratch files, running databases with high write volume, or continuous logging. If you do those, choosing a drive with a higher endurance rating is worthwhile.

What actually kills drives in practice is more often controller failure or a firmware fault than worn-out cells, and that failure mode is abrupt rather than gradual. This is important because it undermines the intuition that a drive will warn you before dying. Mechanical drives often give audible or performance warnings; solid state drives frequently do not.

The monitoring data most drives expose includes a wear indicator and a general health assessment, and checking it occasionally is worthwhile, particularly on a drive several years old.

The practical conclusion is not to worry about write endurance in ordinary use, but to treat any single drive as capable of failing without notice and keep backups accordingly. That advice is unchanged from the mechanical era; only the failure mode differs.