Beltane is a cross-quarter celebration, meaning it’s halfway between an Equinox and a Solstice (the other cross-quarters are Samhain, Imbolc, and Lughnasadh or Lammas). As such, it is marked by astrological features rather than calendrical ones. People note its passing on the calendar because it’s easier for most people to think that way, but Beltane rarely falls on May 1st.
I’ve been reading a fascinating book, “Destruction of the Sabbath”, by Christopher Tyreman and Brad Vornholt of The Chronicle Project (which is an amazing bit of linguistic investigation). While the book is specific to the calculation of the Jewish Sabbath, it brings up a point that is pertinent to any ancient marking of days. There is probably a reason that The Ancestors observed not only Solstices and Equinoxes (if they were solar), but their mid-points as well. Samhain and Beltane are when the veil thins, so knowing the apex of that cycle is important. Imbolc and Lughnasadh are about self improvement (the immanence or internal opposites to the transcendent or external veil holidays), and knowing the apex of that cycle is important as well.
If following the solar wheel is not your strong suit, you can still make a point of celebrating holidays when they actually are. The Archeoastrology website has an Earth Clock that shows the dates of the upcoming solar holidays.