I became able to downvote after reaching 500 karma. The minimum requirement might have changed to 1000 since then, I forget. Even after reaching that karma amo

I became able to downvote after reaching 500 karma. The minimum requirement might have changed to 1000 since then, I forget. Even after reaching that karma amount, you are only able to downvote comments within a day of their posting. After a day, only upvotes are possible.