According to a new Bank of America survey, 16 percent of millennials — which BoA defined as those between age 23 and 37 — now have $100,000 or more in savings.

That's pretty good, considering that by age 30, you should aim to have the equivalent of your annual salary saved. The median earnings for Americans between 25 and 34 years old is $40,352, meaning the 16 percent with $100,000 in savings are well ahead of schedule.

How much should you have stashed away at other ages?

While the amount you need in savings is highly personal, and specific dollar amounts can be arbitrary, money expert at Intuit Kimmie Greene has a simple formula to help you figure out if you're setting aside enough money.

In your 20s: Aim to save 25 percent of your overall gross pay, Greene tells CNBC Make It. "That 25 percent is the combination of 401(k) withholdings, matching funds from your employer and any cash savings that you have," she notes. "It can also include debt repayment.

"Just make sure your lifestyle expenses don't exceed 75 percent of your gross income."