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Free tool
Your memory fades on a predictable curve — and a few well-timed reviews flatten it. Set how much you want to learn below and see your review schedule, how many reviews lock a card into long-term memory, and how spacing beats studying once.
Study a card once and never review it, and this model puts your recall at about 4% after 30 days. Spacing a handful of reviews keeps it near your 90% target instead.
At a 90% target, review each card roughly this far after first studying it:
These figures are estimates from a standard forgetting-curve model (stability 9.5 days, ×2.5 per review), not a guarantee — real recall depends on the material and on you. In Koydo, you never set this by hand: the app schedules every review for you automatically.
After you learn something, your ability to recall it decays over time — the forgetting curve. The calculator models recall as it falls, then schedules a review at the moment it reaches your target. Each successful review strengthens the memory, so the next review can wait longer: days, then weeks, then months. That widening gap is the whole idea behind spaced repetition.
Raise your retention target and reviews come closer together; lower it and they spread out. Either way, a handful of spaced reviews keeps recall high for a fraction of the effort of cramming.
Grounded in the research
Spacing your practice and recalling answers (rather than re-reading them) are two of the most replicated findings in learning research. We list the studies — and where every flashcard comes from — on our sources & methodology page. New to these ideas? Start with our plain-English guide to how to study smarter.
It's a tool that estimates when to review what you're learning so it sticks. You enter how many cards you want to learn and your target retention, and it shows a review schedule and how your memory holds up over time, based on the forgetting curve.
In this model, roughly four to five well-spaced reviews are enough to push a card into long-term memory (stability of about a year). Each review is spaced further apart than the last — days, then weeks, then months.
There's no single best schedule — it depends on your target retention. A common pattern is to review about 1 day, 3 days, a week, a couple of weeks, then a month or more after first studying. Lower your retention target and the gaps stretch out; raise it and they tighten.
No. This calculator is here to show how spacing works — in the Koydo Flashcards app the timing is handled for you automatically, so you just study what comes up each day.
It uses a standard, transparent forgetting-curve model and is meant to illustrate the idea, not to predict your exact memory. Real recall depends on the material and on you. The research behind it is on our sources page.
You just saw the schedule. In the app, you never set it by hand — Koydo brings each of our 15 million+ human-curated cards back exactly when you need it.