This site explains how to calculate in your head (in often less than one second) the day of the week for any calendar date. It also explains how to calculate the day, month or year when one of those other elements of a date is unknown but the day of the week is known. There is no faster or simpler formula out there.
Option for Calculation
There are numerous ways to change this formula to suit someone's differing abilities in doing such things, and this writer will leave it up to your imagination to figure them out. However, there is really no simpler way to calculate this formula than what you see. But if there is one change that could be made, it would be to add in to step 1 the addition of the value for the century (and not do it in step 2). This way, step 1 would add the first three parts of any date, the Month, Day and Century, and step 2 would deal with the year. It was originally added to step 2 for a reason that is not of critical importance and so it can just as well be done in step 1. For some people that might be easier. But decide in the very beginning which option you prefer because it will be vary hard to change later. If you go this optional route, the first step would be calculating the Month-Day-Century value and the second step the two-digit year value. Although this option is slightly simpler, it is not as pure as the process shown and Blogger would not recommend it.