The Half-life of Software
The half-life of Software is the time required for a half of Software developed today to disappear from the market. Today the Half-life of Software is 4 years. The number I found analyzing the lifetime of 200+ discontinued Software.
Histogram of lifetimes of 200+ discontinued Software. Median values is 4 years.
Detailed histogram of lifetimes of 200+ discontinued Software, each bin here is one year.
There is an intriguing connection to Kruchten's hypothesis about five-year half-time of software engineering ideas, concepts, tools, and methods.
Philippe Kruchten. "The Biological Half-Life of Software Engineering Ideas", IEEE Software, 2008.
Don Leavitt. "Most Runs Have Short Useful Life, Research Indicates", Computerworld Vol. XI, No. 30, July 25, 1977, page 21
An IBM study indicates that application programs, on average, have a very short life (14 months).
Data sources: