Just discovered a bank glitch, but I don't know if you can gain any np with it. When I deposit neopoints, my np on hand doesn't change (idk if this is with everyone). Depositing np again doesn't work (error), but when I deposited np with 'upgrade your account' it did work. So if you have 1mil on hand you can deposit 2mil. (and your np on hand would still be 1mil).
But when you withdraw any neopoints your np on hand will show the np you actually have, so you'll have to withdraw 2mil to have 0 np again on hand (if you withdraw 1mil you'll have -1mil on hand). So theoretically you gain np (in your bank) if you never withdraw something.
I hope that makes any sense.. my English is bad
Your english was fine. Its pretty pointless unless you already have 1B pure and you want to double it and just pay off the negative with the interest you receive.