Create this calculated field and put it to the Filters shelf, set to True, it will filter out everything greater than today.
You don't mention if your data contains values for previous years, but if it does, you will need to do what Andrew says, but adding in a YEAR function:
Drag that to filters and set to True.
If your data contains values for prior years and future dates, you can use something like this:
([DateField]<=Today()) AND (YEAR([DateField])=YEAR(TODAY()))