Eighty-one chapters, so it goes round about four and a half times a year. Today's is picked by the date: day of the year, mod 81, plus one.

Translation: James Legge, The Tao Teh King (Sacred Books of the East vol. XXXIX, 1891), public domain, via Project Gutenberg #216. Text not edited, only split up. The paragraph numbers are Legge's.