How many flashcards should I study a day?

Add 15 to 25 new cards a day and review whatever is due. With spaced repetition the review pile settles at roughly 10 to 20 minutes a day; more new cards than that and the pile grows faster than you can clear it.

How often should I review flashcards?

Not on a fixed schedule. Review each card just before you would forget it: the next day, then a few days later, then a week, then weeks. Spaced repetition apps calculate this per card from how well you answered; on paper, a Leitner box with 3 to 5 compartments does the same job roughly.

Should I write flashcards by hand or use an app?

Use whichever you will actually review. Paper is fine for a few hundred cards. Past that, an app wins because it tracks the schedule for every card, works on your phone in spare minutes, and can generate cards from text so you spend the time reviewing rather than writing.

Why do I forget flashcards I already learned?

Because getting a card right once does not store it for good. Memory decays on a curve, and each successful recall at the right moment flattens that curve. If you only review a card when you feel like it, you review it too late or not at all. Scheduling fixes this, not more effort.

Are flashcards good for learning languages?

They are the best tool for vocabulary and the wrong tool for grammar and speaking. Use them for words and set phrases, with an example sentence on the back, and practise grammar and conversation elsewhere.

How to Study With Flashcards Effectively (What Works)

Flashcards work when you use them to recall, not to recognise. Say the answer out loud before you flip, grade yourself honestly, keep one fact per card, and let a schedule decide when each card comes back. Here is how to set that up, on paper or in an app, and the mistakes that make flashcards feel useless.

Quick Answer

One fact per card. A question on the front, one answer on the back.
Recall before you flip. Say or write the answer, then check. Looking at the back first is reading, not studying.
Grade yourself honestly. "Got it", "almost", "no". The grade decides when the card returns.
Space the reviews. Right cards wait longer each time; wrong cards come back tomorrow.
Daily, short. Fifteen to twenty minutes a day beats two hours on Sunday.

Why flashcards work (when they do)

Two findings from memory research explain the whole method. The first is retrieval practice: pulling an answer out of memory strengthens it far more than reading it again. The second is the spacing effect: a review spread over days beats the same number of reviews done in one sitting. A flashcard forces retrieval (if you answer before flipping) and makes spacing easy (because each card is a separate unit you can schedule).

Flashcards stop working when either half is missing: when you flip too early and just recognise the answer, or when you review the whole deck in order every day so that the spacing never happens.

How to make cards worth reviewing

One fact per card. "What are the three branches of the US government?" is three cards, not one. A card with a list on the back gets graded "almost" forever.

Ask a question on the front. "Mitochondria" on the front and a paragraph on the back is a note, not a card. "What does the mitochondrion do?" with "Produces ATP (the cell's energy)" is a card.

Both directions for vocabulary. For a language word, make one card from your language to the target language and one back. Recognising a word and producing it are different skills.

Add context on the back. An example sentence, a mnemonic, a picture. The front stays short; the back can carry whatever helps the answer stick.

Make cards from what you are actually studying. Your textbook chapter, your lecture notes, the article you read. Downloaded decks are fine for standardised material (anatomy, JLPT vocabulary), but a card you wrote from your own material is one you already half-know.

How to review

Say the answer before you flip. Out loud, or write it. This is the single step most people skip, and it is the one that does the work.

Grade honestly, with three levels. Right without hesitation, right after a struggle, wrong. Apps call these "easy / good / again". Marking a struggle as "easy" sends the card away for weeks and you forget it.

Let wrong cards come back the same session or the next day. Do not keep hammering a missed card ten times in a row; once more at the end of the session, then tomorrow.

Shuffle. Reviewing in the same order teaches the order, not the content.

Stop when the due pile is empty. Studying cards that are not due is the time sink. The schedule is doing its job; trust it.

Spacing on paper: the Leitner box

If you use paper cards, use three to five boxes. New cards start in box 1 and are reviewed daily. A correct answer moves a card up one box; box 2 is reviewed every three days, box 3 weekly, box 4 every two weeks. A wrong answer sends the card back to box 1. This is a rough version of what spaced repetition apps do per card.

Spacing in an app: SM-2 and friends

Apps track a schedule for every single card. The common algorithm is SM-2 (used by Anki and Flashi), which lengthens the gap after each correct answer and resets it after a wrong one. You open the app, review what is due, close it. The deck can be thousands of cards and the daily session still fits in a coffee break, because most cards are not due on any given day. A fuller explanation is in what is spaced repetition and how does it work.

The practical difference between apps is how much work it takes to get cards in. Anki needs each card typed or a shared deck downloaded ($24.99 on iPhone). Flashi is free on iPhone and builds a deck from a pasted word list or chapter, so the time goes into reviewing. See free flashcard app for what the free plan includes, and flashcards for language learning for per-language deck advice.

A daily routine that holds

Morning, 5 minutes: review what is due.
After class or reading: turn today's new material into 15 to 25 cards (or paste it into an app and let it draft them, then fix the wording).
Evening, 5 to 10 minutes: review the new cards once, plus anything still due.

That is 15 to 20 minutes a day. Kept up for three months, it is roughly 1,500 to 2,000 facts in long-term memory, which is a conversational vocabulary in a new language or the core of a semester course.

Mistakes that make flashcards feel useless

Flipping before answering. You recognise the answer and feel like you know it. You do not.
Too much per card. Long backs mean permanent "almost".
Reviewing everything every day. Exhausting, and it removes the spacing that makes the method work.
Making cards you never review. A beautiful deck studied once is a notebook.
Only reviewing before the exam. Spacing needs days between reviews; a single cram session gives it none.

Sources

Roediger & Karpicke (2006), "Test-enhanced learning: taking memory tests improves long-term retention" (retrieval practice).
Cepeda et al. (2006), "Distributed practice in verbal recall tasks: a review and quantitative synthesis" (spacing effect).
Leitner, S. (1972), So lernt man lernen (the Leitner box).
SuperMemo SM-2 algorithm description (Wozniak, 1990).