It’s simple, really. Suppose you have $2000 to invest. You also have a credit card that’s charging an annual interest rate of 20%, and you have $2000 charged on the card. Let’s look at two scenerios:
Scenerio A: You use the $2000 to pay off the credit card bill. Interest earned = 0.
Scenerio B: You invest the $2000 in an account that pays 7% annual interest. 7% of $2000 is $140; you’ve just earned $140 from your investment. Hurrah!
But remember, you’ve got to figure that negative credit card interest into the equation. 20% interest. 20% of $2000 is $400. You’re PAYING the credit card company $400 this year. So your net yearly interest total is +$140 - $400 = -260. Not only did you not earn a penny overall, your investment strategy actually cost you $260!
In fact, if you do the math, you’ll discover that you’d have to invest $5714.29 in that 7% annual interest account just to earn the $400 it’s going to take to offset that $400 credit card interest payment! $5714.29 invested at 7% just to break even at the end of the year - which is exactly what you accomplished in scenerio A simply by taking the $2000 and paying the credit card debt off.
Since essentially no investments pay returns even close to the interest rates that most credit cards charge, it doesn’t make sense to put any money into ANY investment vehicles until AFTER you’ve paid those credit cards off. In my example, paying off the credit card leaves you at least $260 better off at the end of the year - and in the long run, that’s what matters, how much cash you actually have in your pockets, not numbers on a bank sheet. NOT paying -20% interest is the equivalent of receiving a +20% return.