Compounding interest
If you were to invest $10,000 at the age of 25, by age 65, that $10,000 investment will have grown to $361,099, at a 9% rate or return.
If you were to put away $50 per month starting at age 25, by age 65 your total investment would be $24,000 and you would have accumulated $235,822, at a 9% rate of return.
