It generally takes between five and 10 minutes to boil Brussels sprouts, depending on factors such as the size of the vegetables, the amount of water in the pot and the heat settings on the stove top. The best way to tell when Brussels sprouts are thoroughly cooked through is to make sure that a knife inserted into the sprouts slides in easily.
To effectively boil Brussels sprouts, using more water allows the water to boil again after adding the vegetables, which lowers the overall cooking time. When the water is hot, add a pinch of salt then add the sprouts. It is a good idea to keep the pot uncovered during cooking as this enables acids from the sprouts to escape.