Spacing: distribute your practice over time#

Imagine you have six hours to learn something — a list of vocabulary, a set of formulae, the parts of a flower. You could sit down and grind through all six hours tonight. Or you could do one hour a day for six days. Same total effort, same material. Which leaves you remembering more next month? It’s not close: the six short sessions win, and they win by a lot. This is the spacing effect, and it’s one of the most reliable findings in the whole science of learning. Next I’ll show you why it works and how to put it to use without keeping a calendar in your head.

Spaced beats massed — every time#

Cramming all your repetitions into one block is called massed practice. Spreading the same repetitions across separate sessions is distributed (or spaced) practice. When researchers pit the two against each other, distributed practice wins consistently — across word lists, facts, skills, children and adults, and across delays from minutes to months.

The single best summary comes from Cepeda and colleagues, who pooled the results of well over a hundred experiments stretching back more than a century. Their verdict was clear: spacing your study reliably produces better long-term retention than massing it, and the advantage grows the longer you wait before the test. Nick Kornell put it in terms any student feels in their gut — he had people learn with flashcards either crammed or spaced, and spacing beat cramming so consistently that he titled the result plainly: spacing is more effective than cramming.

Here’s the part that trips people up. Massed practice often feels better while you’re doing it. Run through the same ten cards five times in a row and they start to feel easy — so you conclude you’ve learned them. You haven’t; you’ve just made them temporarily fluent. Spacing feels harder in the moment because you’ve forgotten a little between sessions and have to work to recall it. That effort is the point. The mild struggle of dragging something back from the edge of forgetting is exactly what cements it. Don’t trust the feeling of ease — trust the spacing.

Why a gap helps#

If repetition builds memory, why would waiting between repetitions help? A few things are going on.

You beat the forgetting curve. Memories decay fastest right after you learn something, then more slowly. A review placed just as a memory starts to fade does far more work than one piled on while the memory is still fresh. Reviewing something you already remember perfectly is nearly wasted effort.
Each gap forces a real retrieval. When you come back after a day, you can’t just coast on what’s still echoing in working memory — you have to genuinely pull the item back up. That act of retrieval is itself a powerful learning event (I cover it in its own right under retrieval practice).
You vary the context. Each session happens in a slightly different mood, time of day and setting. Your memory ends up tied to more cues rather than to one narrow situation, so it’s easier to reach later.

There’s a practical ceiling worth knowing about. Within a single session, piling on more and more repetitions gives you less and less — once you can recall something cleanly a couple of times, hammering it ten more times that same evening barely moves your long-term retention. Those extra reps are far better saved for tomorrow. This is the real reason ten minutes a day beats an hour once a week: the hour spends most of its time above the point of diminishing returns, while the daily sessions each land fresh.

How wide should the gaps be?#

The honest answer from the research is wider than feels comfortable. People reliably under-space. As a rule of thumb, the gap between reviews should scale with how long you need to remember something: studying for a test next week wants gaps of a day or two; knowledge you want for years wants gaps that stretch into weeks and then months.

Earlier learning advice (including earlier editions of this manual) leaned hard on a specific trick: expanding intervals — review after one day, then three, then a week, then a fortnight, each gap longer than the last. The logic is appealing, and expanding schedules do work well. But I want to be straight with you: the evidence that an expanding schedule beats a simple equal-interval one (reviewing at a fixed spacing every time) is mixed. Sometimes expanding wins, sometimes equal intervals match or beat it. So don’t agonise over the perfect ramp.

What actually matters, in order:

That you space at all — this is the big win, worth far more than the schedule’s exact shape.
That the gaps are long enough — err on the side of longer.
That you lengthen the gaps as material sticks — give the easy items longer holidays and bring the stubborn ones back sooner.

Beyond that, the precise pattern is a detail. A consistent habit you’ll actually keep beats a clever schedule you abandon.

Let software do the scheduling#

Tracking review dates for hundreds of facts by hand is miserable — the old approach of a review calendar or a spreadsheet works, but it doesn’t scale. This is exactly what spaced-repetition software is for. Tools like Anki automate the whole thing: you make digital flashcards once, and each day the app hands you precisely the cards due for review and nothing else.

The mechanism is simple to use and clever underneath. When a card comes up, you try to recall the answer, then rate how it went. Get it easily and the app pushes the next review further out — days become weeks, weeks become months. Stumble, and it brings the card back soon and rebuilds the interval from there. Easy cards quietly drift to the back; hard cards get the attention. You spend your minutes only where memory is actually wearing thin.

Modern versions go further. Anki’s current scheduler, FSRS (the Free Spaced Repetition Scheduler), fits a model of your forgetting to your review history and aims each card at a retention target you choose — say, a 90% chance you’ll still recall it when it next comes due. Set the target, do your reps, and it works out the calendar. (The much older SuperMemo program pioneered this idea decades ago; today’s free, open tools have made it mainstream.)

A few tips to get the most from it:

Start early and keep daily. Add cards as you learn, and do a short session every day. Skip a week and the backlog piles up fast.
Make good cards. One idea per card, in your own words. Garbage in, garbage out — the scheduler can’t rescue a vague or overloaded card.
Trust your honest rating. The whole system depends on you grading recall truthfully, not generously.
Don’t over-load it. Add new cards at a sustainable pace; a thousand in week one just buries you.

The takeaway#

Same total effort, spread out, buys you dramatically more durable memory than the same effort crammed. So break study into short, regular sessions; let the gaps grow as material sticks; and don’t trust the easy feeling of cramming — it lies. For anything you need to remember for more than a few days, set up a few flashcards in a tool like Anki and let it schedule your reviews. Ten minutes a day, and the forgetting curve quietly stops being your problem.