Is there a certain formula that will give you a ball park figure of x amount of credits will apply in interested to say 100 Billion credits?

principal x rate x time = interest

2,000,000,000 x .02 = 40,000,000 daily interest on 2B

default rate is 2%

That is a simple straight up calculation. Here's a compound interest calculator:

http://www.moneychimp.com/calculator/co ... ulator.htm

disclaimer: I don't know the exact compound calculation TWGS uses.

I don't know about the mathmatics myself. But 50Billion will net you 1Billion in Interest every 24hrs. 100Billion should net you twice the interest in the same amont of time.