Over the past five years, there's been some very good news for retirement savers. According to a recent study by Fidelity, there has been a 29% increase in employers offering Roth 401(k) plans during that time period. 

Roth 401(k) accounts have some significant benefits over other types of retirement accounts. And, as Fidelity explains, they're increasingly popular among younger workers. If your employer is one of the many new companies offering access to this type of account, it's worth considering whether you should be taking advantage of it. 

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What is a Roth 401(k)?

A Roth 401(k) has some similarities to a traditional 401(k) in that you can sign up to have contributions taken directly out of your paycheck and invested in it. But there are a few big differences.

First and foremost, when you invest in a Roth 401(k), you aren't allowed to make a pre-tax contribution to your account as you do with a traditional 401(k).

Instead, your investments are made with after-tax dollars. But, once you've reached your retirement years, distributions are tax-free. So you can take money out and it will not be subject to income tax at all -- you'll get to keep the entire amount of your distribution instead of giving a piece to Uncle Sam.

Why should you invest in one? 

Roth 401(k)s provide two huge advantages over traditional 401(k) accounts.

The first, as mentioned above, is the tax-free distributions. Most seniors are on a fixed income, so not having to give up a portion of your investment account distributions can be a lifesaver if it leaves you with more money to spend on the necessities as a senior.

Second, any distributions that are taken from your Roth 401(k) aren't going to count when the IRS determines if you owe Social Security tax. See, retirement benefits from the Social Security Administration aren't taxable at all until provisional income exceeds $25,000 as a single filer or $32,000 as a married joint filer. After you've reached these thresholds, you could owe tax on up to 85% of your entire Social Security check.

But since a Roth 401(k) distribution isn't going to count in provisional income, you can take as much money out of this investment account as you want without worrying about the fact that your decision to do so will end up reducing your Social Security checks.

Getting tax-free funds from your two most important sources of retirement income -- your Social Security checks and your savings -- can leave you with much more to spend when you need it. And, if your tax bracket is higher in the future than it is when you're working, you'll also maximize your total tax savings by using a Roth 401(k). Since tax rates remain near historic lows now and government debt keeps growing, there's a very real chance this will be most people's situation. 

If your employer is one of the growing number that's begun offering access to a Roth 401(k), you should seriously consider the significant benefits the account provides and think about taking advantage of it for your retirement savings.