How do I use a date typed in a cell to create a range for another formula?

I have a monthly report that I run to produce reports for timeliness based on a 1-Month, 3-Month, 6-Month, & 12-Month range. What I have been doing every month when I add in the previous month's numbers is adjusting each of my formulas to grab the range I am looking for. This takes a ton of time. I'm looking for a way to be able to type in a date to a cell & have my formulas automatically discern the range based on the date. What I have so far:

=SUMIFS($E$7:$E$500,$D$7:$D$500,">=2/1/15") where my numbers are in E7:E500 & my dates are in D7:D500

This formula is spitting out the correct information I am looking for. The problem I'm coming across is that the person that is taking over this task is not as Excel-savvy as I am & adjusting the formulas makes him uncomfortable. There are also 16 formulas per customer & anywhere from 10-30 customers whose numbers are pulled a month. I'd prefer to have a cell specifically for him to type in 2/1/15 (or whatever date applies at the time) & have the formula pull the date from that cell with a formula something like this:

=SUMIFS($E$7:$E$500,$D$7:$D$500,">=D1") where D1 is the cell the date is entered into

Is there a way to do this?

Try

=SUMIFS($E$7:$E$500,$D$7:$D$500,">="&D1)

That worked perfectly, thanks!

You're welcome.