I honestly don't know. I would say quite much, but it does not feel like that: I do not review all my cards at one time in the day (I have notifications periodically nagging me if there are still due cards, so I don't forget, and they aren't too much bother) Another nice trick is to make more, smaller decks. When I see that there are 120 cards in one deck for review, I am not that ecstatic about that. If those same cards are split into 4 decks with 30-30 cars, I don't even think about it. Generally, 20 cards are play, they don't even register, and 80 seems to be the other end, that starts to feel a bit too much. (And the actual number of cards never changed)

If I somehow miss a day, though, that can make things indeed messy.