Editing 401(k) (section)

===Highly compensated employees (HCE)===
To help ensure that companies extend their 401(k) plans to low-paid employees, an IRS rule limits the maximum deferral by the company's highly compensated employees (HCEs) based on the average deferral by the company's non-highly compensated employees (NHCEs). If the less compensated employees save more for retirement, then the HCEs are allowed to save more for retirement. This provision is enforced via "non-discrimination testing". Non-discrimination testing takes the deferral rates of HCEs and compares them to NHCEs. In 2008, an HCE was defined as an employee with compensation greater than $100,000 in 2007, or as an employee that owned more than 5% of the business at any time during the year or the preceding year.<ref name="US CODE Title 26,414q">{{cite web |url=https://www.law.cornell.edu/uscode/text/26/414-#q|title=US CODE Title 26,414(q) |publisher=Cornell University Law School |year=2007 }}</ref> In addition to the $100,000 limit for determining HCEs, employers can elect to limit the top-paid group of employees to the top 20% of employees ranked by compensation.<ref name="US CODE Title 26,414q"/> That is, for plans with the first day of the plan-year in the 2007 calendar year, HCEs are employees who earned more than $100,000 in gross compensation (also known as 'Medicare wages') in the prior year. For example, most testing done in 2009 was for the 2008 plan-year, which compared 2007 plan-year gross compensation to the $100,000 threshold in order to determine who was an HCE and who was an NHCE. The threshold was $130,000 for 2020, and is $160,000 for 2025.

The actual deferral percentage (ADP) of all HCEs as a group cannot exceed 2 percentage points greater than all NHCEs as a group. This is known as the ADP test. When a plan fails the ADP test, it essentially has two options to come into compliance. A return of excess can be given to the HCEs to lower the HCE ADP to a passing level, or it can process a "qualified non-elective contribution" (QNEC) to some or all of the NHCEs in order to raise the NHCE ADP to a passing level. A return of excess requires the plan to send a taxable distribution to the HCEs (or reclassify regular contributions as catch-up contributions subject to the annual catch-up limit for those HCEs over 50) by March 15 of the year following the failed test. A QNEC must be vested immediately.

The annual contribution percentage (ACP) test is similarly performed but also includes employer matching and employee after-tax contributions. ACPs do not use the simple 2% threshold, and include other provisions which can allow the plan to "shift" excess passing rates from the ADP over to the ACP. A failed ACP test is likewise addressed through return of excess, or a QNEC or qualified match (QMAC).

There are a number of "[[Safe harbor (law)|safe harbor]]" provisions that can allow a company to be exempted from the ADP test. This includes making a "safe harbor" employer contribution to employees' accounts. Safe harbor contributions can take the form of a match (generally totaling 4% of pay) or a non-elective profit sharing (totaling 3% of pay). Safe harbor 401(k) contributions must be 100% vested at all times with immediate eligibility for employees. There are other administrative requirements within the safe harbor, such as requiring the employer to notify all eligible employees of the opportunity to participate in the plan, and restricting the employer from suspending participants for any reason other than due to a hardship withdrawal.