Traditionally, the most popular match was 50% of up to 6% of pay, Reiskytl says. As the number of defined-benefit pension plans declined, many companies moved to bolster their 401(k) match, and while the most common is still 50% on 6%, 100% on 6% is now a close second, followed by 100% on 4% and 100% on 5%, Reiskytl says.

The fact that most companies don't match on contributions exceeding 6% of pay in part reflects inertia, he says, as well as government safe harbor regulations, which say 401(k) plans can avoid nondiscrimination testing to ensure the plan doesn't favor highly paid employees by following certain guidelines, one of which is that the company match should apply to no more than 6% of pay. "The migration toward 6% and not above 6% is being influenced by government regulation," Reiskytl says.

In fact, he says, 401(k) plan participants should be saving a far higher portion of their salaries than 6%. An Aon Hewitt analysis of 2 million workers that took into account their access to other sources of retirement income, such as Social Security and pension plans, found that to ensure a comfortable retirement, on average, employees should be saving roughly 13% to 14% of their pay.