How to make flashcards from lecture slides (and which slides to skip)

To make flashcards from lecture slides, don't turn every bullet point into a card. Pick the few ideas per lecture that the exam can ask about, write each one as a question you have to answer from memory, and put the answer in your own words on the back. Then review them spread over days, not all at once the night before.

A deck of forty slides usually gives you ten to twenty good cards, not two hundred. The cards that help are the ones that make you think ("why does a price ceiling cause a shortage?"), not the ones that make you recognize a phrase ("price ceiling: ___").

The rules below hold up whether you use paper cards, Anki or an app that builds them for you.

Why flashcards work, and when they don't

Flashcards work because they make you pull an answer out of memory before you see it. That act of retrieval is what makes things stick, much more than rereading. It's the testing effect, and a large review of study techniques by Dunlosky and colleagues rates practice testing among the most useful strategies a student can use.

They stop working in two common situations:

• When you flip too early. If you glance at the question and turn the card over, you're rereading with extra steps. The pause before you flip is the whole point.
• When the card is a copy of the slide. A card that says "Mitochondria: powerhouse of the cell" trains you to complete a phrase. On the exam, the question will be about what the mitochondria do and why that matters, and that card never made you think about it.

A flashcard is a question you answer, not a slide you reread.

Step 1: choose which slides deserve a card

Go through the deck once and sort the slides into three groups:

1. Card material. Definitions you'll need to use, the differences between similar concepts, the steps of a process, cause and effect, and anything the lecturer said would be on the exam.
2. Context. Title slides, outlines, history, a photo of the author. Read them once; no card.
3. Problems and diagrams. Worked examples in engineering or economics, reaction mechanisms in organic chemistry, a labeled diagram in anatomy. These need a different kind of card (more below) or practice problems instead.

In an intro economics lecture on supply and demand with thirty-five slides, around twelve cards is a reasonable number: the difference between a change in demand and a change in quantity demanded, what shifts each curve, what a price ceiling and a price floor do, and how to read the effect of each on a graph.

Step 2: write questions, not phrases

Each card should ask something you could be asked. A few patterns that work for almost any course:

• Why or how: "Why does a binding price ceiling cause a shortage?" Back: at that price, more people want to buy than sellers want to sell.
• Difference: "SN1 vs SN2: what's the key difference in the mechanism?" Back: SN1 goes through a carbocation in two steps; SN2 is one step with backside attack.
• Apply: "A contract was signed by a 16 year old. Is it valid?" Back: the rule on capacity in your jurisdiction, and the exception.
• Example: "Give a real example of a negative externality." Back: your own, not the slide's.
• Diagram, with the image: paste the diagram with labels hidden and ask what each one is. Image occlusion in Anki or a simple screenshot with boxes does this.

Rules that save you later:

• One idea per card. If the answer has five parts, split it, or turn it into "list the five steps" and accept that it's a harder card.
• The answer in your words. Copying the slide's sentence lets you recognize it without understanding it.
• Add where it came from. "Lecture 4, slide 12" on the back. When you get it wrong, you go back to that slide.

Step 3: review them spaced out

The other half of flashcards is when you review them. In an experiment by Kornell, studying a deck of flashcards spread out over time worked better than cramming the same cards in small batches, even though cramming felt more effective to the people doing it.

A simple schedule that works without any app:

• Day 1: make the cards the same day as the lecture and go through them once.
• Day 2 or 3: go through them again. Cards you got right move to a "later" pile; misses stay.
• After a week: the later pile. Anything you miss goes back to the front.
• Before the exam: all the cards, mixed across lectures.

Apps like Anki do this scheduling for you. What matters is that the cards you miss come back sooner than the ones you know. More on why in spaced repetition.

Should you let an app make the cards?

There are now many tools that turn a PDF of slides into flashcards in seconds. They save real time, especially with long decks. The tradeoff is that writing the card yourself is part of what makes you learn it, so a deck someone else made, person or AI, will feel easier than it is.

A good middle ground: let a tool draft the cards, then go through each one and rewrite the ones that are just phrases copied from the slide. Delete the ones you'd never be asked about. You keep most of the time savings and most of the learning.

One option is Filmina, a web app that explains your lecture slides out loud. Its Practice section builds flashcards and seven other kinds of questions from your own slides and notes, so there's nothing to write, and the cards you miss come back the next day while the ones you know come back further apart. It's free to start, with a monthly limit on practices. If you're deciding between tools, there are comparisons with Quizlet and Knowt. If you prefer writing your own cards, Anki is still excellent and free on desktop.

Common mistakes

• Too many cards. Two hundred cards per lecture is a sign you copied the deck. You'll stop reviewing them by week three.
• Only definitions. Exams in most courses ask you to apply and compare. Mix in why, difference and example cards.
• Reviewing only the cards you know. It feels good and teaches nothing. Shuffle, and spend your time on the misses.
• Making cards the night before. At that point, practice questions or past papers give you more per hour. Cards pay off when they're made early and reviewed often.

Flashcards are one way to practice recall. If you want the bigger picture, start with active recall, and for explaining ideas instead of memorizing them, the Feynman technique.

Frequently asked questions

How many flashcards should I make per lecture?

Usually ten to twenty for a typical deck of slides: one per idea the exam could ask about. If you're making many more, you're probably copying bullet points instead of choosing.

Is it better to make your own flashcards or use pre-made ones?

Making them yourself helps you learn, because you have to decide what matters and put it in your own words. Pre-made or AI-generated cards save time; if you use them, edit and delete before you study.

Are flashcards good for understanding or only memorizing?

Both, if you write them as questions about why, how and what's different. Cards that only complete a phrase train memorization of that phrase, and little else.

How often should I review my flashcards?

Spread out: the day you make them, a couple of days later, then a week later, with the ones you miss coming back sooner. Reviewing the same deck many times in one session feels productive but is forgotten faster.