When you're young, retirement can seem too far off to think about. And if you're putting off saving for it, you're not alone: Just 31 percent of millennials are contributing to a retirement account, a new survey from Earnest, Amino and Ipsos finds.

Some experts say that if millennials don't change their habits they'll miss the boat completely. The longer you wait to start saving, the farther behind you'll fall and the more you'll miss out on compound interest, which is what can cause your wealth to snowball over time.

"Many of us tend to say, 'I'll get to retirement savings later,' or 'I have all the time in the world,'" certified financial planner Carrie Schwab-Pomerantz tells CNBC Make It. "Consider the 'minus 10 percent rule': If you're in your 20s and you put aside at least 10 percent, you should have a relatively comfortable retirement at age 65.

"But if you wait until your 30s, you have to save 15 percent to 20 percent of your income. And in your 40s, you have to save 30 percent."

Other experts recommend setting aside at least 10 percent of your income as soon as possible. One report suggests that young people should sock away 20 percent of their income if they want the same level of retirement income adequacy as today's retirees.