Ugh...the firecalc button used to spawn a new window on the old board, on this one it replaces the current view and wipes out everything you had typed in the quick reply.
Anyhow, you put in the amount you plan to retire with and enter all dates (for social security, pensions and whatnot) for their dates of actual occurrence.
One way I think you can "game" firecalc to do some planning is to put in your current amounts, expected time frames and whatnot, and add your income in as a portfolio withdrawal "decrease" effective immediately.
Then what'll happen is that your income will offset your spending (presumably) and over time increase your holdings, which will gain money, and you should be able to see the point at which you'll have your desired stash.
I'm sure I used it that way once for a test, but it was a long time ago, I dont recall the details, and i'm sure the next questions will be around how to do this properly...
And i'm not smarter than Dex. And there are no stupid questions...