I have just over 19 months sober now, so while I couldn't tell you the exact day I know the 1st signals a new month for me. Some people find counting very helpful, some don't.
In the past I stopped counting because I told myself it was making me crazy, but truthfully it was the beginning of me stopping my focus on sobriety, and recovery, and I ended up finding myself drinking again.
Definitely do what works for you, but I agree with Dee about the slips, it is very easy to start rationalizing.