October 30th
Permanent link to this comic: http://xkcd.com/656/
Image URL (for hotlinking/embedding): http://imgs.xkcd.com/comics/october_30th.png
[[A kid dressed up in a lab coat and goggles is standing on a neighbor's doorstep.]]
Kid: Trick or treat!
Neighbor: Nice Doc Brown costume, but today's October 30th.
Kid: Great Scott, I must have overshot!
{{Title text: Not enough houses on your block? Just hit them at 30-year intervals from here to 2300 and get 10x the candy.}}