Calculation Background Of Salary Structure We Follow

Can I know the Brief Knowledge about what the reason for calculqting basic 50% in metro cities and others 40% Is there any particular standard which is followed coz we know its Basic 50% , HRA - 25 % , PF 12.5% but why IS IT... Who created it and why it differ in some organization ???

The condition of 50% in Metro and 40% in other cities is for HRA not for Basic. This is due to the fact the Income Tax Act allows HRA exemption as below:
The Least of following is exempt as HRA:
1. 50% of Basic+DA for Metro Cities (40% for others)
2. Rent paid - 10% of Basic+DA
3. Actual HRA received
There is no law which prescribes Basic to be maintained at certain %age of Gross Salary. However, generally companies maintain Basic vs Allowances ratio as 50:50 or 60:40
Rajiv