To figure out what Year of Our Lady Discord it is, the curious person may add the current Gregorian year to 1166 (11 + 66 = 77, which is two sevens; two from seven is five. Eris had returned to us that year, and from then on we have been living in Her radiance.
The incurious person could do very much the same thing, but doubtless would not be nearly as satisfied with the resultant knowledge.
It gets a little dicier if the year you're interested in was before 1 Gregorian - you would then have to subtract the year from 1166. Prior to 1166 BCE Gregorian . . . well, we need heavier drugs for that.
You can use ddate Perl script , ddate Ruby Gem or simply type ddate in Linux console