Software development time?

Question

Programming

Good afternoon!
Quite often, books use a strange formula to calculate software development time. And how do you calculate the time for which you implement the software?

Answer 1

The most accurate assessment is achieved when you work according to Agile, you estimate only a small scope of tasks based on the experience of solving similar ones and lay an additional 20-30% on changes in requirements. If the task is new - up to 50% -60%. If the solution to the problem is unknown, 4 hours are allocated for research, only after which an assessment is made.
For projects that cannot be conducted using agile, I recommend that you read this material.

Answer 2

https://youtu.be/xPPCzryZK44?t=1895