Larian Studios Forums Baldur's Gate III Baldur's Gate III - General How are the percentages calculated?

I thought you roll a d20 to hit, but sometimes I get 97-99% to hit, which is impossible on a d20 of course.
If only on a roll of 1 I fail thats a 95% chance to hit.. so how is it possible I sometimes get these weird chance to hit numbers? Does anyone have the formula?

Thanks.

This has to do with advantage/disadvantage calculation. For example, if you have 75% chance to hit but you have a disadvantage, it becomes 56% (0.75 * 0.75 = 0.5625).

When you have advantage, you roll twice and take the higher roll (and similar for disadvantage you take the lower roll).