Spaced repetition

Medkit uses FSRS to show you each card right before you would forget it. Not so early that you waste time, not so late that it's already gone.

The idea in one sentence

Every time you review a card, Medkit updates three numbers that describe the state of your memory of it:

What it measures	What it means
Stability	How many days the memory holds before your chance of recalling it drops to 90%. It grows every time you get it right.
Difficulty	How hard that particular card is for you, on a scale of 1 to 10. It goes up when you miss.
Retrievability	How likely you are to recall it right now. It drops on its own as days go by.

With those three, Medkit works out the next ideal day to show you the card again. Reviewing at that moment is what fixes the memory long term with the least effort.

FSRS stands for Free Spaced Repetition Scheduler. It's the algorithm that decides when and in what order each card comes up. It replaces older methods like SM-2 with a more accurate memory model.

In practice

There is nothing to configure. Study what comes up each day and the algorithm handles the rest.

What the buttons mean

When you answer a card you pick one of four options. That tells Medkit how well you remembered it, and it adjusts when the card comes back.

Button	When to use it	Effect on the interval
Again	You didn't remember it.	Comes back right away, within minutes.
Hard	You remembered it with a lot of effort.	Grows a little.
Good	You remembered it with normal effort.	Grows just right.
Easy	You remembered it instantly.	Grows a lot.

You can also answer with the keyboard. The full list of shortcuts is in How to study.

Why one card comes up before another

Each card has its own rhythm. One that gives you trouble comes back often until it settles. One you already know gets spaced out further and further, to days, weeks, and then months. That's why two cards you studied on the same day can reappear at very different times.

Within a session, Medkit shows you the ones you were already learning first, and the new ones after.

Target retention

Medkit aims for you to recall around 90% of your cards at the moment you review them. That target decides how often they come up. Raise it and you review more often and forget less, but you study more. Lower it and you study less at the cost of a few more lapses.

Target retention and other parameters are adjusted in Settings › Study preferences. If you don't touch them, Medkit uses recommended values that work well for most people.

The math, under the hood

Retrievability falls over time according to the card's stability S. Medkit schedules the review when that probability drops to your target retention.

R(t) = \left(1 + F\,\frac{t}{S}\right)^{d}

t is the days since the last review and S the stability. The exponent d is the decay, which sets how fast the curve falls: FSRS-6 doesn't fix it in advance, it learns it. F is derived from d so the math lines up with the definition of stability: when exactly S days have passed, you have a 90% chance of recalling it.

You don't need to understand the formula to use Medkit: it's here to show that behind the ideal day there is a measurable model, not a hunch.

If you fall behind

Due cards are not lost. They pile up and come back as soon as you pick things up again, starting with the most urgent.

There is no penalty for missing a day. If you come back after a break, you'll see more pending cards than usual. That's expected and it evens out within a few days.

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