We invest all of it in a compound interest-bearing account. Let's say that the money is invested in a shoe factory. It sells the shoes and gathers back the total money supply and returns it to the investor. To increase the money supply under the present system, it has to be borrowed by someone from a bank. These facts are not clearly visible because there are vast numbers of loans being made and extinguished on a daily basis.
Banks spend a large part of the interest back into circulation.
However, this interest-spending does not increase the money supply. It simply keeps money in circulation. In addition, the total amount of interest and debts that are not repaid are repudiated through business losses, repossessions and bankruptcies.