The number 18 is very significant in the Mahabharata. The original name of the epic – Jaya – represents 18 in numerological terms (Ja -8, Ya – 1), the war happened for 18 days, the Bhagavadgita has 18 chapters, the combined strength of the two armies was 18 akshouhinis, the epic has 18 parvas (chapters) and so on!
Anandatirtha Prathishtana 
Hello Hariprasad,
Numerologically Jaya – 1+1+1+1=4 . How it is 18?
let me know?
Vasudha.
Hello Vasudha,
Ja is the eighth amongst the varnas (ka kha cha ccha and so on)
Ya is one in its set (ya ra la va).
And in our tradition, the number from a particular word is always derived starting from the end. Hence Ya-Ja = 18.
Regards, Hari