In an STP, till the money is parked in a debt scheme, it will incur an expense ratio. Compare the expense ratios of various debt schemes before choosing one for the STP. When you keep the money in a savings account and start a SIP, there is no expense ratio in a savings account. However, banks require you to maintain a monthly average balance (MAB). If the MAB is not maintained, there will be MAB non-maintenance charges.