Hi CLJordan8... I am having a similar issue... I just noticed, in the past few weeks, that any "automatically created" Birthday entries in Calendar (from the Birthday or Anniversary fields in a Contact record) are off by one day. The odd thing is that they show correctly on my iPhone and my iPad, just not on my iMac nor my MacBook Pro. And, if I edit the contact record in OS X, it reverts back to the incorrect date in a few moments (maybe after Contacts synchronizes with my Exchange server?) However, the dates all show correctly on my iPhone and my iPad.
My iMac is running Mojave, and my MacBook Pro is still running High Sierra, so it does not appear to be isolated to the new OS X version.
I've opened a case with Apple Support... If I get an answer I'll update you here as well.