Its easily done, your lifestyle is hectic, busy with work or simply having that well deserved yearly vacation but it’s best not to delay in either renewing that residency permit or applying for another visa. The fines depend purely on your country of citizenship and can be pretty steep if you’re caught out.
Officially there is a maximum of 10 days grace period where anyone with an expired visa or residence permit can leave Turkey voluntarily without any penalty BUT only some immigration officers will abide by this so do not rely on it.
Any overstay will incur at the minimum a fine of 25 US Dollars for the 1st day plus 5 US Dollars per day from the 2nd day of overstay. Saying that, virtually no immigration officers seem to know this and will charge a random figure. So the fine maybe more or less than the official figures, but appear to be around 100tl for each month overstayed.
Payment of overstay fines must be in cash.