Crash rate

Crash rate measures how often an app crashes relative to its usage, typically expressed as crashes per session, per user, or as the percentage of sessions affected by a crash. It is one of the core stability metrics tracked through crash reporting tools embedded in the app.

It is commonly calculated as crash-affected sessions ÷ total sessions over a period, and can be broken down by app version, device model, OS version, or geography to isolate which combination is responsible for a spike. This differs from mean time between failures, a reliability metric more common in systems and hardware contexts that measures the average operating time between failures rather than a rate over a fixed session count. Crash rate is also distinct from ANRs (application-not-responding events on some platforms), where the app freezes without fully crashing — both are stability signals but are usually tracked and reported separately.

Crash rate matters because stability problems directly damage retention and app store ratings, and a spike after a release is one of the clearest, fastest signals that a rollout needs to be halted or rolled back. The main pitfalls are averaging crash rate across all users when a crash is actually concentrated on one device model or OS version, and measuring crash rate over too short a window after a release before enough sessions have accumulated to be statistically meaningful.