Day trading is defined as the purchase and sale of a security within a single trading day.
1) With a margin account, both settled and unsettled funds can be used for day trading. With the net account value no less than $25,000, you have unlimited access to day trading. For an account below $25,000, you can make 3 day trades within 5 successive business days. Your remaining day trades will be automatically counted and displayed in the Home tab.
2) With a cash account, only settled funds can be used for day trading. For example, if you have $1,000 settled funds, you can make five day trades for $200 each, or you can use all the money for just one day trade. When you run out with settled funds, you are no longer eligible for day trading. If you insist to buy stocks with unsettled funds and sell them out before (T+2) settlement, you will trigger GFVs.
For more examples on day trading, please visit "Glossary-Day trading" with a hyperlink.