What is a crowd calendar?
A crowd calendar is (as you might guess) a calendar that purports to predict daily crowd volume at a theme park?
What are the top Walt Disney World crowd calendars?
As far as I know, no one has undertaken a comprehensive study comparing crowd calendars, but the best and most popular Disney ones can be found at: Disney By Age, Touring Plans, Undercover Tourist, WDW Prep School, and Easy WDW.
What's the controversy About Crowd Calendars?
There are basically two schools of thought on Walt Disney World crowd calendars. The first is that they are a necessary part of optimizing your Walt Disney World trip. Time is money at WDW, so spending more time in line because of crowds is a waste. Being stuck in a crowded park is moreover an unpleasant experience.
The alternative line is that crowd calendars are useless. Their predictive merit is suspect since day-to-day variations in crowds are mostly random. The rest is basically common sense because it is an unavoidable part of your own planning. Parents don't need a crowd calendar to tell them spring break is going to be crowded because they're considering spring break for the same reason as everyone else!
what are the best things about crowd calendars?
First, the good.
You can use crowd calendars to avoid the big problems you might not know about. You should definitely check a crowd calendar or two before deciding when to take your trip. If you don't have kids (we don't), you might now know when spring break is (spring, I guess?). You might not know which days Florida or California (for Disneyland) kids get off school. And so on. Using the crowd calendars to make sure you're not picking an awful time is a reasonable thing to do. WDW Prep School has a great example of a useful crowd calendar that provides an outline of what is going on at the parks and the reasons to expect bigger or smaller crowds.
What's not as great about crowd calendars?
Parks Are Too Dynamic To Predict
I'm firmly in the camp that the crowd calendars are basically useless on a day-to-day basis. You can see this just by comparing them. The best ones frequently disagree, some having a day as the busiest at a park while others say it will be completely empty. Moreover, the parks change too much. Do you think the history of crowds at Animal Kingdom and Hollywood Studios will be useful at all in the coming years? No way! But if crowd patterns at two parks are changing, they'll change at the other two as well.
Focus your energy elsewhere
Finally, even within their margins of accuracy, there are so much more important things to be worrying about than crowds. Fastpass+ availability and ADRs (advance dining reservations) are the biggies. If your favorite Epcot restaurant is only available at 4PM on a Tuesday but your partner says that won't work because Tuesday is a red day that week and you'll be at Animal Kingdom, where things are green, then go find yourself a new partner. If there is a way that over-planning can ruin a Disney trip, it is over-reliance on crowd calendars.
The truth is, if you're planning carefully, you'll be minimally impacted by crowds. Once you've rope dropped and used your first set of Fastpasses, you'll be able to check wait times around the World to see where to head next. You'll have planned to get all your rides in via Fastpass, rope drop, or, last resort, waiting in line. But those you're waiting in line for? They shouldn't be the rides with waits of an hour+. Double the crowd might take one of your lines from 20 to 40 minutes, but that's within the margin of error of Disney's line times anyways (joke, sort of).