Quantified self

Quantified self refers to the practice, and the loosely organized movement around it, of tracking personal data, steps, sleep, mood, spending, screen time or any other measurable behavior, in order to notice patterns and make deliberate changes. The term was coined around 2007 by Wired editors Gary Wolf and Kevin Kelly, though people had kept personal logs and diaries long before smartphones and wearables made continuous tracking effortless.

In practice it spans simple manual logs, fitness trackers and smartwatches measuring signals like heart rate variability, and personal-finance tools built for net worth tracking or savings rate. This differs from the player tracking data collected on professional athletes by a team's dedicated systems: quantified-self data is typically gathered by an individual, about themselves, for their own use, with far less standardization or oversight.

The practice matters because ongoing self-measurement can reveal patterns, a link between sleep and mood, or spending and stress, that are hard to notice without data, supporting more deliberate habit change. Common pitfalls include tracking so many metrics that no single one gets acted on, mistaking correlation in a small personal sample for a real causal effect, and abandoning a tracking habit once the novelty wears off, which breaks the continuity the insight depends on.