Guides · Memory
The forgetting curve is not your enemy. It is a timetable, and once you can read it, you can beat it with less total study time.
Here is the uncomfortable truth about a study session: most of what you learn in it will be gone within a few days unless you come back to it. This is not a personal failing. It is how memory works for everyone, and it was measured carefully over a century ago. The good news is that the decay is predictable, which means you can schedule around it.
Spaced repetition is the practice of reviewing material at increasing intervals: soon after you first learn it, then a bit later, then later still. Each review happens right around the time you would otherwise start to forget, and each one pushes the next forgetting point further out. The result is that a topic you might have reviewed ten times before an exam under a cramming approach needs perhaps four or five well-timed reviews instead, and stays with you long after the test.
Cramming works, in a narrow sense. If you spend four hours on a topic the night before, you will remember a lot of it the next morning. The problem is what happens afterward: the memory decays almost as fast as it was built, so by the final exam, or by next year's course that assumes you know this, it is mostly gone and you have to relearn it from scratch.
Spacing the same four hours across two weeks produces a slightly worse score the next morning and a dramatically better score a month later. For anything cumulative, which is nearly every school subject, that is the trade you want.
You do not need an algorithm to get most of the benefit. A fixed schedule is easier to stick to and works nearly as well. Here is one that fits a typical school week:
| Review | When | What to do |
|---|---|---|
| Day 0 | The day you learn it | Take notes, then do a short closed-book recall before you stop (see the active recall guide). |
| Day 1 | Next day | Answer your questions or cards from memory. Rewrite anything you missed. |
| Day 3 | Two days after that | Same again. This one usually catches the things that felt solid on day 1 and were not. |
| Day 7 | One week | Quick review. Most cards should be fast now. Spend your time on the stragglers. |
| Day 14 | Two weeks | Final check. Anything still shaky goes back into the day-1 rotation. |
After day 14, you can safely leave the topic for a month or more and it will still be there when you need it for a cumulative exam. Look at the numbers: five short sessions, most of them under ten minutes, in place of one long painful night.
The simplest way to run this without software is a "review calendar." Every time you learn a new topic, write its name under today's date, then under the dates one, three, seven, and fourteen days out. Each morning, look at today's date and review whatever is listed. The Study Planner can do this if you enter each review as its own dated task.
If you would rather not do the bookkeeping, the Flashcard Builder handles it automatically. When you rate a card as "got it," it schedules the next review further out; when you rate it "still learning," it brings the card back sooner. You just open the tool and review whatever is due.
Spaced repetition is best for things with a definite right answer that you need to recall quickly: vocabulary, dates, formulas, definitions, anatomical structures, the steps of a process, the causes of an event. It is a poor fit for skills that need practice rather than recall, like writing an essay or solving an unfamiliar problem type. For those, space the practice instead: do a couple of problems of each type every few days rather than twenty in a row once.
It is also a poor fit for material you have not understood yet. A flashcard that says "What is entropy?" will not teach you what entropy is. Understand first, then use spacing to keep it.
Suppose you learn two new topics per week in a class. After the first few weeks you will have a steady state where every day has one or two reviews due from different points in the schedule. In practice that is ten to fifteen minutes a day per class. Over a semester that adds up to less total time than a few cramming nights, and you walk into the final already knowing the material rather than hoping you can rebuild it in a weekend.