4 days late-bfn

Just wondering if any others had any related experiences. Af is always on time for the last 3 years. We have been ttc for 9 months. I am now 4 days late and just took my first test for this month. It was negative. I guess wondering if there is still a chance for bfp, or how late people had to test for bfp.... or could just be another month. Have had no symptoms other than typical monthly.