How Many New Flashcards a Day? The Science

It is Sunday evening, you open a new 250-word deck, and you are in the mood. The cards fly by. Two hours later the whole deck is done, and it feels like the best study session in months. On Thursday you open the app again, and 257 cards are waiting.

I have done this myself, more than once. Some people who sign up for Words on Repeat do it too: they finish a whole beginner deck in their first two or three days. It feels fast. But research says it is a slow way to learn words. This is not about willpower. It is simply how memory works.

Below I explain six studies in simple words. Then I show what learning a whole deck at once does to your reviews. At the end you get a simple answer to the question in the title.

What the research says

1. Spreading it out beats doing it all at once

This is one of the oldest findings in memory research. In 1885 Hermann Ebbinghaus tested his own memory. He found that 38 repetitions spread over three days worked as well as 68 repetitions done in one day. Spreading them out saved him almost half the work.

Since then, people have tested this hundreds of times. In 2006 a team led by Nicholas Cepeda looked at 317 experiments together, from 184 scientific articles. Most of them tested how well people remembered words and facts. Overall, spreading study out clearly won. Few things in learning science are this solid.

2. With flashcards, cramming feels better but works worse

Nate Kornell (2009) tested this with flashcards. Students learned word pairs in two ways. Spread out: all the cards in one big pile, so each card came back only after many other cards. Crammed: the cards in small piles, so each card came back quickly.

Spreading the cards out worked better for 90% of the students. But after the first session, 72% thought cramming had worked better.

That is the trap. When a card comes back soon after you last saw it, it is easy, and easy feels like learning. When it comes back later, you have to search your memory for it. That small effort is exactly what makes the word stay.

3. Sleep between sessions saves work

In a study by Stéphanie Mazza and colleagues (2016), 40 people learned 16 Swahili words (with their French meaning). Twelve hours later, they practiced the words again until they knew all 16. Half of them slept between the two sessions. The other half did both sessions on the same day.

The people who slept needed about half as many tries to relearn the words (about 3 instead of 6). A week later they remembered about 15 of the 16 words. The other group remembered about 11. Six months later, the sleep group still remembered more than twice as many.

Sleep helps the brain keep new memories. When you spread a deck over a week, every group of new words gets a night of sleep before you practice it again.

4. Fewer sessions, further apart

Psychologist Harry Bahrick and three members of his family learned 300 foreign words each and practiced them over several years (1993). They wanted to see which schedule worked best. They tested their memory up to five years after the last session.

13 sessions eight weeks apart worked about as well as 26 sessions two weeks apart. So the bigger gaps gave the same result with half as many sessions.

5. The right gap depends on how long you want to remember

In a study with more than 1,350 people (Cepeda and colleagues, 2008), the researchers changed the gap between the first study session and a review. To remember something for a week, the best gap was roughly one to three days. To remember it for a year, it was roughly three to five weeks. A spaced repetition app chooses these gaps for every card by itself. But it works best when the new cards are spread out from the start.

What a whole deck in one evening does to your reviews

The studies are about memory. There is also a practical side, and you feel it much sooner: reviews. Every new card you learn today comes back for review over the next days and weeks. Cards you learn together come back together.

To show this, I ran a simulation with the scheduler we use in Words on Repeat (FSRS). I used the same 250-card deck twice: once with all 250 cards learned on day 1, and once with 30 new cards a day. To keep it realistic, about 1 in 10 answers is wrong.

Learning everything at once means 528 cards on day 1 (each new card comes back a few times on its first day). Then 257 cards on day 5 and 220 on day 19, with almost nothing in between. At 30 a day, the busiest day has 101 cards, and there is never a wall.

That day-5 wall is where many people give up. They have not lost interest. But 257 cards on a Thursday evening take an hour they do not have, and the next day the pile is still there.

So how many new words a day?

There is no magic number, but there is a sensible range. This is a recommended pace, not a limit. Every new card brings more reviews over the next weeks, so the best way to choose is by the time you have each day. The table below is a rough guide, not a result from the studies:

For comparison, Anki, the best-known flashcard app, suggests 20 new cards a day by default. At 20 a day you learn about 600 words a month.

When going faster makes sense

Sometimes speed matters more than saving time: an exam in six weeks, a trip next week. Then more new words a day is fine. Just follow three simple rules:

1. Review every day. The extra words only pay off if you see them again on time.
2. Do not add lots of new words just before a day you cannot study. A day off is fine. A day off right after a big batch is what builds the wall.
3. Count back from the date. 1,300 words in 16 weeks is about 12 new words a day, not 300 on the last weekend. Our German B1 article shows how to do the math for an exam.

How Words on Repeat helps you keep a steady pace

We built the same idea into the app, as a suggestion rather than a rule:

• Spaced repetition takes care of the reviews. FSRS brings each card back just before you would forget it, so a little every day is enough.
• Exam Kits suggest a daily number up to your exam date. Enter the date and the kit shows how many new cards a day get you through every word in time. There is no daily limit on new words in a kit. You can go faster if you want.
• Trip Kits split 50 phrases over five days, about ten a day, so day one is already useful if you fly tomorrow.
• Your streak counts days, not cards. One short session a day keeps it going, and that daily habit is exactly what the research rewards. If you miss a day, a streak freeze keeps it alive.
• While you study, the app suggests about 30 new words a day. It is a hint, not a stop. You can change the number or turn it off in Settings, under New words a day.
• A practice test shows what has really stuck. It asks 20 mixed questions on one of your decks (choose the meaning, listen, type the word, fill the gap), with an optional 10-minute timer. Start one on the Quiz page, for example a few days after you finish a deck.

Want to try the steady way? Pick a beginner deck from the public decks. Learn 20 new words today and 20 tomorrow. If you want to know why we forget in the first place, the science of spaced repetition explains the forgetting curve.

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