move data from sheet1 to sheet2 based on date in column1 of sheet1

I would like to have some (or all) data from "Assignments" moved to individual "month" tabs. ie. if the date in column A is in October, then rows A-K would populate the "October" tab. Then I want to make updates on the "October" tab and have it update the corresponding items in the "Assignments" tab. (Vice versa would be okay too).

It sounds like what you want to do would create a circular reference within Excel. Without a workaround (such as two separate Assignments tabs, only one of which you update), or VBA, I don't think this can be accomplished.

I've only had a chance to play with this a bit but it looks great. Didn't know the formula would have to be that complex. Thanks for all the work. If use the "assignments" tab for all the data input, I might have a 2-3 thousand rows over the next few years, with as many as 2-3 hundred per month. If I have 12 monthly tabs with 250 rows with your formula in each cell will that bog down the spreadsheet at all?