Studying with Spaced Repetition

Spaced repetition isn't a study trick — it's a response to a fact about memory: the interval between reviews matters more than the number of reviews. Cramming ten reviews into one evening builds a fragile memory that fades in days. The same ten reviews spread out over weeks, timed just before you'd otherwise forget, build a durable one. FSRS is the algorithm Sona uses to find that timing for every card, individually, based on how you've actually rated it.

What FSRS is doing behind the scenes

Every time you review a card, FSRS updates two numbers for it: how difficult it seems to be for you, and how stable your memory of it is. From those, it estimates how long you can go before you're likely to forget it — and schedules the next review right around there. A card you find easy drifts toward longer and longer intervals. A card you keep struggling with comes back sooner, more often, until it stabilizes.

None of this is something you configure. There are no "ease factors" or interval settings to tune, the way older systems make you manage. You just rate each card after you see it, and the schedule adjusts itself.

Rate honestly, not hopefully

After you flip a card, you rate it Again, Hard, Good, or Easy. This is the one place where getting it right actually matters — it's the entire signal FSRS has to work with.

• Again — you didn't get it. No shame in this; it's the whole point of reviewing.
• Hard — you got there, but it took real effort or you weren't fully sure.
• Good — you recalled it correctly, at a normal pace.
• Easy — it was instant, no effort at all.

The temptation is to rate generously — Good when it was really Hard, because you technically got the answer. Resist it. FSRS schedules the next review based on what you tell it, so an optimistic rating just means you'll see the card again too late, once you've actually forgotten it, and have to relearn it from scratch. An honest Hard now saves you a real miss later.

Study sessions never punish an honest Again — it isn't a failure, it's exactly the information the scheduler needed.

Study is the only thing that touches your schedule

Sona has three ways to go through a deck, and only one of them is FSRS. Study is the real thing — your due and new cards, and every rating you give feeds back into scheduling. Browse is a free, read-only flip through the whole deck with nothing tracked, good for a quick refresher on a bus with no pressure attached. Quiz is low-stakes practice — eight different formats (multiple choice, true/false, written recall, listening, audio choice, sentence building, and a timed matching game, among others) that never touch your schedule at all, so quizzing yourself as much as you want before a test never distorts what Study thinks you actually know.

If you only have time for one of the three on a given day, make it Study — it's the one actually managing what you'll remember next week.

A few minutes daily beats a weekend push

Because FSRS times reviews just before you'd forget, a deck's daily queue is usually small — a handful of cards, not a hundred. That's by design: the whole point of spreading reviews out is that each one stays cheap. Skip a few days and the queue doesn't vanish, it just backs up, and a two-week gap usually means more cards have drifted past their ideal review point than a daily five-minute habit would ever let happen. Short and frequent almost always beats long and occasional here.

Study anywhere, including offline

Any deck you've downloaded works fully offline — Study, Browse, and Quiz all run with no connection at all, including starting a brand-new session, and your reviews sync back the moment you're online again. That's true on the free plan too; nothing about spaced repetition itself is paywalled.

If your queue tends to pile up on days you're commuting or traveling, downloading the decks you review most is worth doing before you actually need it, not after.