Mahine (chandra-maas) ke hisaab se dekhen to:

Purnima (Poonam) ki tithi – Har chandra-maas me sirf ek hi baar aati hai. – Us din chaand poorn roop se dikhai deta hai.

Isi tarah Amavasya bhi mahine me ek hi baar aati hai, lekin paheliyon me aam taur par iska jawab “Purnima” hi diya jata hai, kyunki wo poornima ka chand sabko yaad rehta hai.