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.
Help Desk
Got a comment, suggestion or need help with a problem? Leave a comment at this posting and I'll try to get back to you quickly if that is what is called for. In the meantime, if you have a question, you might visit the FAQs page to see if the answer you're looking for is there, or if you are having trouble with one of the calculations, you might try looking at some of the examples on the examples page.