Creating a workback schedule in Excel with date formulas

Hi Community,

Trying to create a work-back schedule based on user input date. I've done this a long time ago for launch schedules, but don't have the spreadsheet anymore. This is for a nonprofit I'm helping out and trying to stream-line their new employee onboarding process. I tried to find the info but after an unfruitful hour on the hunt for a template or how-tos, I'm hoping someone here can help.

Much appreciated!