Generally, we keep calendars to keep an eye on what's coming up in our life, but Lifehacker reader MoogleLally reminds us that we can use them to remember important dates from the past as well.
Since you'll often need to refer to certain landmarks in life at a later date, it may be easier to keep them all in one place:
I just created a Google calendar called "That One Time That Important Thing Happened" so I could keep track of important dates—my start date at my current job, my move-in date for my apartment, the day of our car wreck, the day of my minor surgery, the last time I checked with my credit card company to see if I could lower my APR, etc.
If you find it too confusing to try and sift through old calendars, reader Chispea lets us know her preferred method of cataloguing these dates:
For me, those dates are few and far between, so I use more of a "captain's log" approach. Using a plain word processing document in Google Docs or Dropbox, I simply write the date and what occurred (with any pertinent information) on the next available line.
Since you're often searching by event rather than by date (i.e. "what was the date of that car accident?"), you may find this method an easier reference. Either way, it's easier than trying to keep those things in your head. Got any of your own tips for keeping track of important events past? Let us know in the comments.