Looking for a solution to Gantt style planning but backwards from due date

edited 12/09/19 in Smartsheet Basics

I'm a transcriptionist and I have multiple transcriptions at a time in my to do pile. These all have due dates and I have a good idea of how long it would take to type them up. Ex, due March 1st need 3 days to type, must start by march 26th. If I have multiples due on March 1st, I can't start them all at the same time so they need to also be conditional. In a Gantt chart I can also input days off.

My biggest question is, in excel I can make a table that calculates the start by date when I input the due date, but this doesnt take into consideration days off, and other transcriptions due around the same time. A Gantt chart shows me how everything flows on a calendar. 

Does anyone have any suggestions for how to do this