The J method: the D0, D1, D3, D7 calendar explained

What is the J method?

D0 (J0 in French) is the day you learn or understand a chapter for the first time. The following reviews are counted from that day: D+1 the next day, D+3 three days later, D+7 a week later, and so on. It’s also written D1, D3, D7. The most often cited calendar looks like D0, D+1, D+3, D+7, D+15, D+30.

The intervals vary from one source to another: some add D+2 or D+10, others push to D+60 for a distant competitive exam. Calendar variants also circulate under other names. All rely on the same idea: space out the reviews, further and further apart, instead of going over everything the day before.

Why does spacing out your reviews work?

The spacing of reviews has been studied since the late 19th century. A 2006 meta-analysis (Cepeda et al.) gathers 317 experiments on memorizing verbal information. It concludes that spreading learning over several days clearly improves what you remember, compared with massed sessions, and that the most effective interval gets longer when the deadline is further away.

The same review stays cautious about expanding intervals (1, 3, 7 days…): the data don’t let us say they do better than even spacing, and depending on the study they help or give similar results. For you, the consequence is practical: space out your reviews and test yourself at each one, without hunting for the perfect calendar.

How do you keep the J method by hand?

Take a sheet or a spreadsheet with one row per chapter and one column per review: D0, D+1, D+3, D+7, D+15, D+30. On D0, calculate and write all the dates in the row. Every morning, look at which boxes fall today.

As a guideline, allow 10 to 20 minutes per review for a chapter you already understand. Watch the load: each chapter you add brings five more reviews, and after three weeks several chapters fall on the same day.

• Step 1: on D0, understand the chapter and write 8 to 15 questions whose answers are in your course notes.
• Step 2: at each review, answer the questions without your notes, then check.
• Step 3: record the result in the cell, for example in green (all correct), orange (a few gaps) or red (many mistakes).
• Step 4: after a red cell, add a review one or two days later, limited to the topics you missed.
• Step 5: if you skip a day, do the review the next day and push back the following ones instead of giving up on the table.

Example: a D-day schedule before a test

Take a history chapter on the Cold War, learned on a Monday, with a test planned for the Friday of the third week, 18 days later. The standard schedule fits almost perfectly, except for its last review.

On D+3, you miss 4 questions out of 10, all about the Cuban Missile Crisis. The schedule has to react to this result instead of carrying on as planned.

Common mistakes and limits of the D-day method

The first mistake is rereading at every D. You recognize the text, you feel like you know it, and the review teaches you nothing about what you forgot. Always start by answering without your notes; rereading comes after, only on what you missed.

The second limit: the method assumes you understood the chapter on D0. Spacing out reviews of a fuzzy topic mostly repeats a confusion. If a cell stays red twice in a row, go back to the explanation in your notes or ask for help before continuing the schedule.

Finally, the manual table quickly gets heavy and does not tell easy topics from hard ones inside a chapter. With a dozen subjects, a card-by-card system becomes easier to keep up, on paper with a Leitner box or in an app.

Automate the D-day method with FSRS in Fichea

A fixed schedule treats every topic in a chapter the same way, yet you can remember a date after two reviews and stumble five times on a mechanism. Spaced repetition software therefore calculates an interval for each card, based on your answers.

FSRS, the algorithm used by Fichea, estimates each card's difficulty and stability, which is roughly the number of days before your probability of remembering it drops to 90%. It schedules the next review when that probability reaches the target level: a well-known card moves further away, a missed card comes back quickly.

In Fichea, you create flashcards from your course notes, check them, then pick Again, Hard, Good or Easy after each card. The schedule shows the reviews planned over the next 14 days. It does not know your exam date and does not send reminders: open it yourself and add a quiz before the test. Spaced review depends on your plan.

Frequently asked questions