When you take a loan from your 401(k), you are taxed on the money you withdraw, Suze says. "When you go to pay it back, you are paying it back with money you have already paid taxes on," Suze says. "So when you go later on in life to withdraw that money again, you're being doubly taxed."
If your 401(k) is through work, Suze says you will be required to pay back any money you've borrowed immediately if you lose your job. If you don't have the money, Suze says that loan becomes taxable income—and you'll pay a 10 percent penalty if you're younger than retirement age.