Your checking account is set up automatically to overdraft from your savings in the event an item is presented for more than is available in your checking. As long as there are sufficient funds in your savings account, the funds will transfer automatically to your checking to cover the presented item.
There are limits to the number of overdrafts that can be done in one calendar month. These limits are set in place by a federal regulation called Regulation D.
Transfers or withdrawals from a savings account without a signature are limited to 6 per calendar month. This is a federal regulation called Regulation D. These transactions include telephone transactions, E*Teller and overdraft transfers. Any transfer or withdrawal in excess of 6 must be completed in a branch or at an ATM.
Click here for detailed information regarding Regulation D.