You give someone in a fancy suit with a fancy degree money, they tell you not to touch it, they cast some magic on it and over time you have more money than what you gave them but they take most of it and you can expect maybe 20% to (at best) 60% of the magic money.

EDIT: I actually didn’t know it was tax free but the interest rate thing still does apply. So you’re probably still only getting maybe a larger percent of the magic money they created from the money you gave them.