Hi
In case of Employee have only Regular Income(/124) in the perticular Month then Taxable amount(/4MI) = Total amount (/434) / 12 (in April).
Incase of Employee have Regular,Irregular income /4MI value gives aproximately like below
Taxable amount(/4MI) = Total amount (/434) / 12 [in April] + after one time tax deduction of Irregular income or Total Irregular Income + /ZBS + carried forward irregular income