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Americans have a veritable smorgasbord of retirement tools at their disposal -- just check out our IRA Center to get a sense of how many retirement options you have and how to get started investing. But no retirement tool may be better than the Roth IRA, which was introduced in 1997. Americans' desire to contribute to the Roth IRA has been gaining steam for nearly two decades, turning it into one of the most popular retirement plans today. The following 17 Roth IRA facts outline why it's become such a go-to retirement vehicle for working-class Americans.

1. Annual contribution limit: For Americans aged 49 and under, the annual contribution limit to a Roth IRA in 2016 is $5,500.

2. Catch-up clause: But the good news for persons aged 50 and up is that a "catch-up clause" exists, which allows seniors to contribute an extra $1,000 per year. In 2016, this works out to a maximum contribution of $6,500.

3. Contributions limits tied to inflation: Roth IRA contribution limits are loosely tied to inflation, and they tend to adjust every few years, assuming we see some degree of inflation. For example, between 2008 and 2012 the contribution limit for Americans ages 49 and under was $5,000, with people aged 50 and over able to contribute $6,000. Between 2005 and 2007, the contribution limit was just $4,000 for persons under 50, while the catch-up contribution for older Americans rose from $500 in 2005 to $1,000 in 2006-2007.

4. Income limits for Roth IRA: Income limits exist on who can contribute to a Roth IRA. Single individuals making less than $117,000 in 2016 are free and clear to max-out their contribution. Earned income between $117,000 and $132,000 can reduce the amount you're eligible to contribute, and earned income beyond $132,000 would disqualify you from contributing to a Roth IRA. Similar figures are observed for joint-filers. Earned income up to $184,000 is acceptable for a full Roth IRA contribution. The phase-out begins between $184,000 and $194,000, and disqualification for contribution hits at $194,000 for joint-filers.

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5. Back-door to a Roth IRA: But have no fear, because a back-door solution to the Roth IRA is here. The IRS allows for one IRA conversion per year, meaning high-income earners who are locked out of contributing to a Roth can convert a Traditional IRA to a Roth IRA once annually. When this back-door approach was introduced in 2010, there was an immediate jump of more than 800% in conversions to the Roth IRA from Traditional IRAs on a year-over-year basis. Just keep in mind that you'll be responsible for paying taxes tied to the conversion, since a Traditional IRA is funded with pre-tax money.

6. You can contribute retroactively: One of the neater perks of the Roth IRA is that Dec. 31 isn't the end-all, be-all when it comes to contributions for a fiscal year. You're free to make retroactive contributions up until Tax Day (usually April 15) of the following year that can count toward the current fiscal year. For instance, money contributed to a Roth IRA on April 15, 2017 can be used to count toward your 2016 annual contribution limit.

7. Separate accounts for married couples: Something worth keeping in mind for married couples is that you can't have a joint IRA. In order to be able to maximize your contributions, you and your spouse must each have separate IRAs for tax reporting purposes.

8. No upfront tax benefits: Unlike the Traditional IRA, which is funded with pre-tax dollars and can result in immediate reductions in your current year taxable income, contributions to a Roth IRA have no effect on your current year taxes.

9. After-tax in, tax-free out: However, money contributed to a Roth IRA is in after-tax dollars. The advantage to this is your money grows completely tax-free for life. In other words, forgoing the upfront tax deduction associated with a Traditional IRA could save you substantially more if your Roth IRA nest egg has grown by a lot over time. Comparatively, the Traditional IRA is a tax-deferred investment tool, meaning accountholders are responsible for paying taxes once they begin making withdrawals.

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10. When you can begin taking withdrawals: Speaking of withdrawals, Roth IRA accountholders become eligible to begin making withdrawals from their account at age 59-1/2.

11. Contributions can be withdrawn anytime: But, here's something interesting with the Roth IRA. Because contributions are in after-tax dollars, accountholders can remove their contributed money (not their investment gains) at any time, for any reason, without incurring any penalties or taxes. Let's assume you're a 40-year old working American who's contributed $40,000 to their Roth IRA over the last decade. If you suddenly need $10,000 to cover an emergency, you can pull out $10,000, or up to $40,000 for that matter, for any reason without incurring a penalty.

12. Five-year wait on investment gains: When it comes to investment gains within the Roth IRA, it's a completely different story. In addition to being over the age of 59-1/2, you can't withdraw investment gains (including earned interest) from a Roth IRA unless you wait at least five years from when you made your initial contribution.

13. No minimum required distribution: Another key selling point of the Roth IRA is the incredible financial flexibility it offers. Whereas a 401(k) or Traditional IRA both have minimum required distributions that accountholders must begin taking by age 70-1/2, the Roth IRA has no such minimum required distributions. You can take as much as you'd like, whenever you'd like, as long as you're over the age of 59-1/2. And if you don't want to take any money at all, that's fine, too!

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14. No age limit of contributions: Additionally, there are no age limits as to who can contribute to a Roth IRA. If you're 75 years old and still trying to build your nest egg, or perhaps working on giving your grandkids a head start on their retirement, you can continue adding $6,500 per year. With a Traditional IRA, contributions must cease by the year you turn 70.

15. Exemptions exist for early withdrawal: There are even exemptions that allow Roth IRA accountholders who are younger than 59-1/2 to make withdrawals without paying a penalty, or perhaps even being taxed. Examples include withdrawing money to pay for medical expenses exceeding 7.5% of your adjusted gross income, paying healthcare premiums if you're unemployed with Roth IRA funds, or using the money for a qualified first-time home purchase (up to $10,000). 

16. Penalties await unqualified withdrawals: If you don't have a qualified early withdrawal exemption, and you're below the age 59-1/2, prepare to pay the piper. Not only will you be responsible for paying ordinary income tax on your Roth IRA gains, but you'll also incur a 10% penalty for your troubles as icing on the cake.

17. Keeps you focused on the long-term: Finally, one of the most underrated aspects of the Roth IRA is that it'll keep investors focused on the long-term. With rules that require investors to wait for five years before taking their investment gains, and not dipping into their Roth IRA prior to age 59-1/2, save for a few exemptions, the Roth IRA encourages Americans to invest in a broad array of high-quality assets.

The Roth IRA isn't even two decades old yet, but don't be shocked if it becomes the most popular retirement tool in America within the next 20 years.