 Third, build an emergency fund of three to six months of expenses. And then fourth, start investing 15% of your income. In your case, if you had no payments but a house payment and you save 15% of your income, well, 15% of $40,000 is $6,000. That's $500 a month. If you invest $500 a month from age 41 to age 61, you will be a millionaire. Wow.