Cost of fixing bugs

Costs are logarithmic; they increase in size tenfold as the time increases. A bug found and fixed during the early stages – requirements or product spec stage can be fixed by a brief interaction with the concerned and might cost next to nothing.

During coding, a swiftly spotted mistake may take only very less effort to fix. During integration testing, it costs the paperwork of a bug report and a formally documented fix, as well as the delay and expense of a re-test.

During system testing it costs even more time and may delay delivery. Finally, during operations it may cause anything from a nuisance to a system failure, possibly with catastrophic as an aircraft or an emergency service.