Question: How long on average does it take to write a whole computer program ?

William Pettersson answered on 13 Jan 2020:

This can be very hard to answer. Some programs that are very simple (say, to just add two numbers together) can be written in a few minutes. Some programs, maybe like complicated video games, might take hundreds of people, and a few years, to write. It all depends on what program you are writing.

Personally, it will take me days to weeks to write the sorts of programs I use.