This is the long explanation of the $1 balance left. (More than 1 of my (adult) kids didn't get it on the short version.
When you spend $500 in January, the bill comes (lets say) jan 31 and it has to be paid by Feb 25. You keep spending on the card in Feb. This new $800 spending will be billed on feb 28, and has to be paid by March 25.
But when the bill closes on feb 25, even though only the jan spending of $500 is due, you don't want the new $800 balance sitting there using up a large % of your credit line. So you pay most of it at the end of the month in which you spent it. Even though the payment is not yet due.