Ovulation question

Ok so I have a stupid question....my periods are pretty much like clockwork, every 28 days. I planned both of my ladies birth months and all. Wellllll I got bronchitis and my period was 6 days late. How would this change my ovulation/fertile days? I found online if today(12/30) is the first day of my period baby would be due 10/05. Fertile days are week of 01/10/16. How accurate do you think it is? Any help is appreciated. TIA.