Rate of return to player is an important characteristic of online casinos. Despite the fact that results of each particular game are random, there is the average payout ratio that is relevant in the long run, and stays almost unchanged.
Let's take slot machine payout percentage of 97% as an example. This means that all online casino slots return to players 97% of their money spent. In this case 3% is the amount online casino earns. 97% payout is the standard value, although there can be lower as well as higher numbers. Average rate of return lies within 95%-98% range. Land based casinos usually return to player less money, that's because they have higher operating expenses.
Players need to understand that the rates are average values, and actual return may vary from declared. In other words, one player can lose all the money during one playing session, while another player will end up winning big. But altogether online casino will pay out 97% of the amount bet.
Usually online casino games have different payouts, but they all exceed 90%. Actual payout percentage can change every month. It generally deviates from the theoretical rate by 1-2%. Average daily and weekly payouts have much higher deviations. This is explained by dispersion.
Unfortunately, online casinos do not specify payout of every game separately. Maximum what you can expect, is the payout of each game category such as: slots, poker, roulette, etc. Payout percentage is determined by an operator, but it can't be lower than a certain value. If the market is regulated, then special organizations make sure payouts are not below official standards. Besides, developers do not produce casino games with low rate of return.
Quite often casinos online get additional help from independent companies that specialize on inspecting payout values. During one month all the game results data is transmitted to a separate server. Only employees of the audit firm can access this server. Findings of the audit are usually published at casino website. This way, online casinos assure players of their honesty.