You can use XIRR for calculating returns. You simply need to keep track of cashflows (transfers between your bank account and Zerodha account), and apply XIRR formulae in excel. Baically you are calculating return on money deployed in your trading account.
I personally feel this as practical and efficient way to calculate portfolio performance as you don’t have to track everyday buy/sell transactions. Let me know if you need any help there. Link below has the summary of my XIRR values, it don’t have the methodology though