The SRS penalty varies a little based on when an item is gotten wrong, but for the most part, I’ve observed a drop of 2 levels. That means the item will show up 3 more times for every mistake.
Because of that, the average number of reviews a day is adjusted by two factors:
- Lessons per day; WaniKani’s SRS system has 8 levels.
- Number of items wrong per day. A worst-case -2 SRS penalty → 3 reappearances
Reviews/day = 8 * |lessons/day| + 3 * |penalty items/day|
R = 8 L + 3 P
Penalty items/day = (1 - Accuracy) * Reviews/day
P = (1 - A) * R
Plug the equation for P in, and we’ll be able to solve for R.
R = 8 L + 3 (1 - A) * R
R (1 - 3 + 3A) = 8 L
R = 8 L / (3 A - 2)
This equation shows us that 1 / (3 A - 2) approximates a review multiplier based on accuracy.
I don’t know how to make a table, so I guess I’ll use bullets. We’ll go with numbers for 10, 15, 20, and 25 lessons/day.
- For A = 100%, the multiplier is 1; 80, 120, 160, 200 reviews/day
- For A = 99%, the multiplier is 1.031; 82.5, 123.7, 164.9, 206.2 reviews/day
- For A = 98%, the multiplier is 1.064; 85.1, 127.7, 170.2, 212.8 reviews/day
- For A = 97%, the multiplier is 1.099; 87.9, 131.9, 175.8, 219.8 reviews/day
- For A = 95%, the multiplier is 1.176; 94.1, 141.2, 188.2, 235.3 reviews/day
- For A = 90%, the multiplier is 1.429; 114.3, 171.4, 228.6, 285.7 reviews/day
- For A = 85%, the multiplier is 1.818; 145.5, 218.2, 290.9, 363.6 reviews/day
With the multiplier being an inverse function “1 / (3 A - 2)”, review accuracy is very important. Lower average accuracy will lead to iterative penalties and consequently, many more reviews. This equation may just be an estimate, but it shows how imperative it is to maintain an average above 67% in order to finish WaniKani in a timely manner.
I hope this helps! (Also let me know if I made any embarrassing math mistakes… :D)