Put all raises toward your 401(k) One good way to increase your retirement savings is to put all raises that you get toward your 401(k) until you reach the $17,000 annual contribution limit for those under 50. "The idea is that if you're making do with what you earn now, you can put your entire raise toward your 401(k) and save for retirement," Regli says. Don't borrow against your 401(k) Many 401(k) plans allow you to borrow money from your account for up to five years, but Regli says you should avoid the temptation. "You're contributing this money for your retirement, so you should try to leave it in your 401(k) for that purpose," she says. On paper, 401(k) loans sound great. You can usually borrow up to $50,000 or 50% of your 401(k) balance (whichever is lower) for any reason, and you generally pay the money back over five years through payroll deductions. There's no credit check, and the interest you pay actually goes back into your 401(k) account -- meaning loans are essentially interest free. But the funds you borrow will be out stocks or other investments until you pay the money back, so you'll miss out on potential gains. "When you take money out of your 401(k), you're not giving it the time in the market that it needs to grow," Regli says. Don't treat your 401(k) like a glorified savings account Companies will often send you a big check with your 401(k) balance if you leave your job -- money many Millennials will run out and spend rather than "roll over" into another retirement account. That's a bad idea, Regli says. "That's money that you're saving for retirement," she says. "If you go out and buy a boat with it, what will you have left for retirement?" Instead of spending your 401(k) proceeds, you should deposit them in a rollover IRA or similar account within 60 days, Regli says. That way, you'll not only keep the money for retirement, but avoid income taxes and early withdrawal penalties on the funds. Better yet, have your 401(k) plan deposit the money directly into another retirement account for you. That will ensure you don't miss the 60-day deadline for avoiding taxes and penalties.