Actually some managers have spreadsheets like:
Scotty /=2;
Dreamer *= 4;
It is a matter of calibration.
The best prediction of a software schedule (in my experience) is what has happened before. The very best prediction comes from a delta from the last project. When there are huge technical unknowns and a new team, roll the dice. How to predict the software effort remains a vexing problem with no certain answers.