Understand every statutory charge that hits your trade.
Brokerage is only part of the bill
Even a zero-brokerage trade carries statutory and exchange charges. These are collected by the broker on behalf of the government and exchanges, so they are identical no matter which broker you use.
Securities Transaction Tax (STT)
STT is levied on the value of your trade. It is higher on delivery (charged on both buy and sell) and lower on intraday and F&O. For options it is charged on the premium and on exercised contracts.
GST, exchange and SEBI fees
GST of 18% applies on the sum of brokerage and exchange transaction charges. Exchange transaction fees and a small SEBI turnover fee are charged on traded value. Individually tiny, together they form most of the cost on a zero-brokerage trade.
Stamp duty
Stamp duty is charged on the buy side only, at rates that vary by segment. It is capped and modest, but worth including when you compute your true break-even on a position.