MAT

Mat stands for Minimum Alternate Tax.It is the tax which is paid by companies.The current rate of tax is 18.5%.If the  normal tax as per total income is less than the tax calculated as per 115JB i.e book profit,then the company is required to pay Mat.Credit for the same would be allowed subject to certain conditions.

https://finance.indiamart.com/taxation/corporate_tax/mat.html

current rate of MAT is 18.50%...

whether every company calculate their tax as per MAT or is their any conditions to calculate tax as per MAT also??

Mostly company calculate their tax as per income tax act. If company is profit in negative figure according to IT act than they have to pay tax as per MAT rules.