Being unaware of most of the provisions Congress put into the landmark retirement law over a year and a half ago could prove costly to investors, writes Leonard Sloane for The Wall Street Journal.

The provisions cover required minimum distributions, types of accounts that can be used for certain retirement-plan contributions, and a whole lot more.

“Lots of rules have changed,” said Sarah Brenner, director of retirement education at Ed Slott & Co. “If you happen to be affected by one of them, it could have a significant impact on your finances.”

According to the changes, there are no more required minimum distributions from Roth 401(k) plans. Contributions to such plans are made after-tax, which means that income tax is paid before the funds go into the plan each contribution. This is also true for Roth IRAs but not traditional 401(k)s.

High earners (those whose annual income exceeds $145,000) aged 50 or older have to put 401(k) catch-up contributions into Roth accounts.

Some spousal beneficiaries of IRAs now get more potential tax-deferred growth. For example, an older spouse who is a beneficiary of an IRA that is owned by a deceased younger spouse will be treated as if they were the age of the deceased spouse. This way, RMDs do not have to be taken until the deceased spouse would have turned 73, which allows for more potential tax-deferred growth.

Starting last year, the penalty for missed RMDs was brought down to 25 percent of the missed amount compared to 50 percent. And if corrected in a timely manner, it can even be cut lower, to 10 percent.

There is now a three-year statute of limitations for missed RMDs, starting with the filing of the income tax return for the relevant year.

Read more about the changes in retirement saving rules in The Wall Street Journal.

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