Calculate IT on LTCG AND STCG for the FY 2025-26

You do not add LTCG/STCG with other income just to check if it is within the basic exemption limit for exempton. Instead, you compute total income including alll sources, then apply tax rules for each component (like LTCG/STCG tax rates). If total income is below Rs.3,00,000 (for individuals ,<60 years), no tax is payable on total income considering basic exemption. 

Long term and short term securities are seperate.

Seperately to be discussed.

Taxability in this case are different.