DecksAnki interval modifier: what it does and how to calculate it
The interval modifier is a multiplier Anki applies to every review interval under SM-2. At its default of 1.00 it does nothing. At 0.80, a card that would have waited 10 days waits 8, so you review more often and forget less; above 1.00 you review less often and forget more. Leave it at 1.00 unless you've measured your retention and want to move it.
Where it is
Deck Options, under Advanced, alongside Starting ease, Easy bonus and Hard interval. It's an SM-2 setting: with FSRS on, the way to change how often you review is desired retention instead.
Measure your retention first
Open Stats for the deck and find the Answer Buttons graph. The correct percentage on the mature side is your mature retention: how often you pass cards with intervals of 21 days or more. Anki's manual expects most people to land around 90% on moderately difficult material. Wait until you have a good number of mature reviews before trusting the number; young cards vary a lot.
The formula
Anki's manual gives this formula, from SuperMemo:
modifier = log(desired retention) ÷ log(current retention)
Use any calculator with a log button, and enter the percentages as decimals.
| Current retention | Target | Interval modifier |
|---|---|---|
| 80% | 90% | 0.47 |
| 85% | 90% | 0.65 |
| 88% | 90% | 0.82 |
| 92% | 90% | 1.26 |
| 90% | 85% | 1.54 |
The 85% to 90% row is the manual's own example: gaining 5 points of retention means reviewing about 35% more often. That's the catch with this setting. Small gains in retention cost a lot of extra reviews, and the cost grows the closer you get to 100%.
Before you lower it
If you're forgetting too much, the modifier isn't the only fix. The manual suggests that spending more effort when you first learn a card, or using a mnemonic, can give you more for less time. Badly made cards are a common cause too; how to write good flashcards and leech cards cover those.
Also check you're pressing Again when you forget. Pressing Hard on a card you didn't know keeps its interval growing and drags your retention down; see Hard vs Again.
Things to know
- It affects future intervals only. Cards keep their current due dates until their next review.
- Correct answers always add at least a day. Anki makes each new interval at least one day longer than the last, so a low modifier can't trap a card at the same interval.
- It's not the same as ease. Ease is per card and changes as you answer; the modifier is one number for the whole preset. See Anki ease factor explained.
In Decks
Decks uses SM-2 with Anki's default settings, which is the same as an interval modifier of 1.00. There's no setting to change it.
Published 2026-10-19.