If anyone could devise a mathematical formula for becoming a millionaire before age 40, it's Charles Glass. The 31-year-old Howard University professor earned a Ph.D. in civil engineering from the University of Colorado, where he conducted research in the microbiological treatment of municipal, industrial, and hazardous waste. By the time he received his graduate degree in 1997, he was fully committed to using his math background to build wealth, primarily by practicing DOFE principle No. 2: to be a proactive and informed investor. Glass learned the benefits of saving -- and the danger of debt -- early on. His parents' willingness to sacrifice their savings to pay for his undergraduate education allowed him to graduate without student loan debt. Lucky for him, because he racked up more than $2,000 in credit card debt on what he says were "college expenses." "When I received my undergraduate degree, I had $2,000 in credit card debt at an 18% interest rate," says Glass. "I was amazed at how the interest rates meant that I gave bankers money for free." He paid off the debt while in graduate school, and then cut his investment teeth by opening a Putnam mutual fund and a TIAA-CREF account. Soon after graduation, Glass landed an assistant professor position at the University of Nevada, earning $49,000. He arranged to have 10% of his salary put in his TIAA-CREF account through payroll deduction, which was matched by the university. He increased his Putnam mutual fund contribution from $200 to $500 a month, and he began placing $300 a month into a money market account to create a six to nine month cash reserve. Financial advisors recommend saving this amount in case of an unforeseen job loss. Glass bought his first home in Reno, Nevada, after learning about the benefits of owning real estate. The purchase was a no-brainer. "You've got the tax write-off from the interest you pay on the mortgage, and you build equity over the time you own the home. And, if you rent the property later, you get depreciation from taxes and can create a positive cash flow from the rental," he says. After accepting his current job at Howard, Glass moved to Maryland, where he purchased his current home in 2000 for $183,000. His salary jumped to $95,000, and he moved to accelerate his plan to become a millionaire by opening his own environmental consultancy firm, ETEC L.L.C., in the fall of that year. He rented his Nevada home for two years before selling it in 2002 for $135,000, reaping a profit. Glass then refinanced his current home, from a 30-year loan at 7% interest to a 15-year loan at 5.25%. He controls his spending by keeping his overall expenses to $1,000 a month. These moves have helped him build a $51,000 TIAA-CREF 403(b) account and a Vanguard mutual fund account worth $100,000. And he's even closer to reaching his million-dollar goal. His current home has appreciated by $77,000 and is now valued at $260,000. To achieve these impressive financial goals, Glass has stuck to three simple rules: FIND ADDITIONAL SOURCES OF INCOME "My whole quest is to use my mind and my intellect to think of ways to build wealth other than just working for 30 years," says Glass. Not content with a $95,000 annual salary, Glass opened his own consultancy firm, which earned $100,000 in both 2001 and 2002. He put $47,000 of those earnings toward his mortgage and another $80,000 into a Vanguard mutual fund. He intends to use the remaining $73,000 to buy a rental property, which will give him another source of income. "I think the best chance for me to grow wealthy at the youngest age possible is to continue to run my business and to buy real estate property under market value, then improve the property and use it for rental income until I'm ready to sell," Glass asserts. SEEK FINANCIAL ADVICE Glass educates himself by reading books on investing and money management. His favorites include The Millionaire Next Door by Thomas J. Stanley (Pocket Books; $14.95); The 9 Steps to Financial Freedom by Suze Orman (Crown Publishing Group; $13.95); Rich Dad, Poor Dad by Robert T. Kiyosaki (Warner Books Inc.; $16.95); and The 7 Habits of Highly Effective People by Stephen Covey (Simon & Schuster; $14.00). LIMIT INVESTMENT FEES Glass changed his mutual funds from Putnam to Vanguard because Putnam charged a 5% fee for mutual funds and for using their services. "I believe in the principle of indexing and minimizing fees, and I didn't like the idea of giving up 5% of my money every time I bought mutual funds," he says. "Life is a constant battle between everyone trying to get money out of your pocket and trying to keep the money you have and make it grow." With his higher salary, the purchase of a new rental property that can appreciate in value, and nine years left to invest before age 40, it appears that Glass' formula for becoming a millionaire is a success.