If Box 1 has swollen past 100 cards and your daily review now takes an hour, the fix has three parts. Stop feeding Box 1. Shrink the cards that keep failing. Drain Box 1 before you touch the higher boxes. Plan on a few days of short sessions spent only on Box 1.

The one thing to know first: almost every number on this page comes from people who run the Leitner system and write about it, not from controlled studies. Treat the numbers as sensible starting points, not measured limits.

What you need

  • Every card currently in Box 1

    Physical or digital. The steps work for both.

  • Blank cards and a pen

    For splitting and rewriting cards.

  • A timer

    Your review time is the measure you will track.

  • A divider or rubber band

    To keep a backlog pile separate from today's pile.

Clearing the backlog, one step at a time

  1. Stop adding new cards

    Put every unstudied card aside. Nothing new goes into Box 1 until it is back under control. The Leitner Method FAQ names pausing new cards as the first fix. The Anki manual gives the same advice for software: stop new cards until you catch up, because adding them while you are behind makes the backlog worse.

    It worked when: the new-card pile sits outside the box, untouched.

  2. Count Box 1 and time one pass

    Note two numbers. The FAQ treats a Box 1 under 30 cards and a 10 to 20 minute review as healthy. It treats a review that keeps running past 30 minutes as overloaded. LeitnerBox.io calls a Box 1 consistently above 50 cards a warning sign.

    It worked when: you have a card count and a minute count written down.

  3. Mark every card you fail

    During that pass, put a tick on the back of each card you get wrong. Over the next few sessions, the cards with several ticks are your problem cards.

    It worked when: a handful of cards carry most of the ticks.

  4. Split the cards that test more than one fact

    Take each heavily ticked card and ask whether it asks for two or more things at once. If it does, rewrite it as several cards, each with one question. Both Active Recalling and LeitnerBox.io list overstuffed cards as a main cause of a Box 1 that keeps growing.

    It worked when: each new card has one question and one short answer.

  5. Throw out duplicates

    Pull any cards that test the same thing. Active Recalling lists this as a fix step.

    It worked when: each fact appears once in Box 1.

  6. Set aside cards you do not understand

    Some cards fail because the idea underneath them was never learned, such as a reaction mechanism you skipped. Active Recalling suggests checking for missing prerequisite knowledge. Move these cards out of the box and go back to the source material before you return them.

    It worked when: every card left in Box 1 is one you understand but cannot yet recall.

  7. Review only Box 1 until it is small

    Skip the higher boxes for now. The FAQ suggests spending a couple of days clearing Box 1 after missed reviews before you go back to normal sessions. If a full pass still runs long, split the box. Keep a front pile you review daily and a backlog pile you work down a fixed number at a time. This borrows the Anki manual's filtered deck approach of working an overdue backlog "at a comfortable, sustainable pace."

    It worked when: Box 1 is under about 30 cards and a pass takes 20 minutes or less.

  8. Restart new cards at 5 to 10 a day

    Bring new cards back slowly. The FAQ recommends 5 to 10 a day to start. Other guides go as high as 10 to 20, but a box that just overflowed is a reason to start low.

    It worked when: Box 1 holds steady for a week instead of creeping back up.

When Box 1 refills anyway

New cards almost certainly came back too fast. New cards pile up quietly: the Anki manual estimates that 20 new cards a day leads to roughly 200 reviews a day once the deck matures. Drop back to 5 a day. If it still creeps, try the slower pace FluentFlash suggests, which is 5 to 10 new cards a week rather than a day.

Some of it is the system doing its job. LeitnerBox.io puts it plainly: "Having cards return to Box 1 is not failure, it's the system working correctly." When one card has failed many times, though, it is usually overstuffed or rests on something you never understood. Go back to steps 4 and 6.

Yes, but the controls have different names. Lower the New cards/day setting, or set it to zero until the backlog is gone. Then use the manual's two filtered decks: one for cards overdue less than a week, studied daily, and one for older overdue cards, worked down slowly. How Anki's scheduling differs from [fixed boxes with pass/fail grading](/leitner-system-vs-anki-for-exam-prep/) is covered separately.

With Box 1 back under about 30 cards and new cards capped, you can return to reviewing every box on its normal days. The next job is getting those days right, so that Box 2 and Box 3 do not pile up the same way.

Which box do you review on which day?

The schedule for 3, 5 and 7 boxes, laid out side by side.

See the box schedule