It depends on the day trading platform and its terms. For example – how many Bitcoins do you want to buy and the payment method you prefer (a debit card payment, a bank transfer, etc.). In addition, there are service providers that claim not to charge you anything for Bitcoin trading (although, in most cases, they factor a small trading fee in the Bitcoin price they quote you). In contrast, others charge a fixed sum (i.e., $1 per transaction), a fixed, or a dynamic percentage (in the case of maker-taker pricing models).