|If you can sort your list of dates in descending order, which is required by the MATCH function if you want to find a value that is greater than the lookup_value, this should work:|
Assume your descending list of dates is in A1:A4 and the date you want to look up is in C1.
If you can't sort your list of dates in descending order, you could create a descending list in another location using the LARGE function and then modify the formula above to search that list. (You could even hide this list if you want)
Let's say your dates in A1:A4 are in random or ascending order and the date you want to look up is in C1. In F1, put this formula and drag it down to F4:
This should create a descending list of your dates in F1:F4 which will get updated if you change the list in A1:A4. The ROW() function generates the k argument for the LARGE function. There are certainly many other ways to generate the k argument, including just typing it.
Now you can use this list by modifying my other formula:
The only other option I can think of is a UDF written in VBA.
Hope that helps!