how often is DP charges levied?
The Demat charges are applicable every time a single or multiples of the same scrip moves out of your demat holdings in a single day.
Whether you sell 1 or 1000 shares of COMPANY ABC in a singe day there is a flat rate charged.
"DP (Depository participant) charges
INR 13.5 per scrip (irrespective of quantity) debited from demat account when stocks are sold. ₹5.5 per MF (irrespective of quantity) debited from demat on redemption. Charged by depository (CDSL) and depository participant (Zerodha)"
Quoted from https://zerodha.com/charges