Figuring out EDD

So the first day of my period is always pretty self-explanatory- pretty heavy/continuous flow. However, this month I had one day of continuous spotting before the full blown bleeding started the following day. Of course this has never happened before and I ended up Which day don't count as the first day of my period in order to figure out my EDD? And yes I know there is only a day variance, but I'm slightly OCD 😜