All casinos and poker rooms, both online and bricks and mortar, take a commission from every pot. This fee is called the rake and is often around 5% of the total pot amount. In order to stop the pot from disappearing, poker rooms tend to limit the rake to a certain amount, normally $3.
Both the fee percentage and ceiling can differ significantly. The online standard is 5% up to $3, whilst bricks and mortar casinos tend to have higher rakes. For example, the Cosmopol Casino takes a rake of 5%, up to a maximum of 100 kr.
Both the percentage and ceiling can also differ significantly depending on the level you are playing at and whether you are playing short-handed or at full tables. Five percent of the pot does not sound so much to most people, especially if the ceiling is set at 2-3 dollars.
But, if you play a lot of poker, the rake ends up being quite a lot in the end. A person who plays several tables at the same time, at low levels and for a long period of time can pay rakes of several hundred dollars per month.