If you are planning a trip and either it ends in the USA or you have to transit through one of the US airports to catch a connecting flight, you can now check the waiting time to clear immigration. CBP (Customs and Border Protection) offers a new tool on their website to do that. Recording of this data started in July 2008 for the busiest airports in the US.
However when you check for your planned trip, you are not checking your trip date, you check the same date one year past and maybe two years past. This gives you an idea of how long the wait time on that particular day will be, tho it’s not a guarantee. Flight arrival patterns can vary considerably by the time of year and day of the week, as well as by time of day. Also be aware that if a flight gets delayed and now it arrives together with another flight, waiting times can increase drastically in that event.
In a previous travel tip of the week (TTOTW) I wrote about to planing your flights to avoid connecting flights in the US if you are connecting to another international destination outside the US. In case your final destination is in the US, also try to connect somewhere else, for example, Iceland, to avoid picking up your bags and checking them again.