Here's how to tell if your old $2 bills are worth anything

• US Currency Auctions are now valuing some $2 bills at thousands of dollars.
• Finding if yours are worth anything is not as easy and checking the mint date.

It might be your lucky day if you've ever saved a $2 bill you came across.

Two dollar bills have been in circulation since the 1860s, and have existed in six different currency types, according to the US Bureau of Engraving and Printing. Since 1928, the bills have featured Thomas Jefferson on its face, with his home, Monticello, or an image of the presentation of the Declaration of Independence, on its back.

Now, the United States Currency Auction, which allows people to sell rare US currency, lists some $2 bills as worth upwards of $4,500. Some rarer, uncirculated $2 bills could be worth up to $20,000, per Morningstar.

But how can you tell if you have a valuable bill or a common one that isn't worth much?

There are a couple of key places on your bill to check out, like the year and seal color.

Bills that have red, brown, or blue seals printed between 1862 and 1917 could be worth up to $1,000, per IndyStar.

And, the older a bill is, the rarer it's usually considered.

Serial numbers and condition of the bill are also important, per MarketWatch.

If the serial number, printed on the left and right sides of the bill's face, starts with the number 1 and was printed in 1976, you could have hit the jackpot — the bill could be worth more than $20,000, per MarketWatch.

Other serial numbers that would interest collectors are "solid" or "ladder" serial numbers. Solid serial numbers are all the same digit, and ladders have digits in ascending order, per MarketWatch.

Of course, the condition of the bill is also a major factor. A good condition note will be worth more for collectors than a damaged one.

Don't be too upset if your bill isn't worth anything — you're not alone in saving them.

According to Dustin Johnston, vice president of Heritage Auctions, Americans seem to really like holding onto the bills, despite the fact that they aren't as rare as we think.

"Americans don't spend $2 bills, because they think they are markedly scarce," Johnston told MarketWatch. "Just in the last five years, they've printed 100 million $2 bills. The fact that they don't circulate and are kept as mementos is a little bit odd. Very few of them have numismatic or collector value."