Supposedly it will take until around the year 2140 before the last Bitcoin is mined. About 75% of Bitcoins have already been mined (under 17 million) so you can see that the mining difficulty is increasing over time. It will get to the point where less than a whole Bitcoin is mined every year. This is one reason why the value of Bitcoins should keep increasing over time as the number of Bitcoins mined every year keeps decreasing.