Keeping track of holidays can be tricky. Google Now is making it a bit easier by giving you countdowns to holidays it recognises.
As Android Police points out, if you create a reminder in Google Now, you will now get a handy little red label that tells you how many days you have left until the event. It doesn't seem to be tied in to your calendar, so custom events won't have their own label (or birthdays, sadly), but hopefully Google will expand it over time. It's also worth mentioning that, since you can see your reminders in Inbox, this is particularly handy.
In our tests, this didn't work on older versions of the Google (formerly Search) app. If you're still on an older version — anything pre-4.0, really — Android Police's sister site APK Mirror has downloads and instructions here. Unrooted users on KitKat or older may have trouble, but rooted users, or those running Lollipop can fix the incompatibility issues. Or you can wait til this version rolls out to everyone. Hopefully it won't be after the holidays.