Favourable days of the lunar month for cutting the hair are:

The 8th to bring longevity,
the 9th to bring attractive energy,
the 10th to bring magnetism,
the 11th to bring intelligence,
and the 26th and 27th to bring happiness.


The 1st, 2nd, 7th, 12th, 16th, 18th, 21th, 25th, 28th and 29th days of the lunar month should be avoided. 
Cutting one's hair on these days will lead to a loss of vitality.

Pl. refer lunar calender for the aforesaid days. 
Tashi Delak.