The forgetting is measurable. Without rehearsal, about 60–70% of new facts vanish in the first day, and the curve keeps eroding for weeks ¹. A card timed to land just before that drop, repeatedly, beats the same hours spent all at once, confirmed across 317 experiments ².

Recall is the active ingredient, not re-reading. Students who took one practice test recalled 50% more a week later than students who re-read the passage ³. Once a fact was answered right once, further studying added nothing; further testing did the work ⁴.

It holds for decades. Adults tested on high-school Spanish 50 years on kept a flat shelf of vocabulary for 25-plus years without rehearsal ⁵. In a follow-up, 13 review sessions spread far apart matched the five-year retention of 26 packed close together ⁶. In medical school, Anki users scored 6–13% higher on their exams regardless of test-taking skill ⁷.

Install Anki. Free on desktop and Android, $25 once on iPhone, free sync, no ads. Pick it unless you have a reason not to.

Start months ahead, not two weeks before an exam: the scheduler needs review history to space anything, and early starters beat late ones at equal card counts ⁷.

The turn comes at two weeks. Cards from day one come back and you remember them.

By six months the deck holds a few thousand kept items: a language you'd dropped a decade ago works again, the chapter you read in winter is recallable in summer. At the year mark, what you reviewed enough has settled into a state where forgetting roughly stops ⁵. The bill is the daily contact you kept up.

For casual learning, Duolingo and similar apps hide lighter spacing in a friendlier shell: lower ceiling, but you open them. For exams that test application over recall, spaced past-paper practice often wins on the same machinery ⁸.