I remember back in 1996 when the Dayton region was split out from the 513 area code and became 937. The 513 area code had lasted from its beginning in 1947, so just under 50 years. 937 is now running out of numbers and an overlay area code, 326, will be added in 2020, so 937 will have lasted about 24 years, about half the time as 513. An overlay eliminates the need to change existing numbers, so only new numbers will be assigned 326, which is a relief. 513 is expected to run out of numbers in 2024, per the report at the second link below, and get an overlay of 283. Expect a 12-digit phone number in your future, when all area codes are exhausted. Ouch.