Your 401(k) retirement plan is probably your single largest financial asset. But what is it costing you to invest? $100 a year? $1,000?

If you don’t know, you’re not alone. More than 80% of plan participants have no idea what their 401(k) charges, an AARP survey found.

That may be about to change. BrightScope, a San Diego start-up that rates 401(k) plans, has just launched its Personal 401(k) Fee Report tool, which allows investors to quickly determine their plan costs — everything from fund expense ratios to plan consulting fees to administrative charges.

Knowing those numbers is essential to your retirement security, since the difference between a high-cost plan and a low-cost one has a huge impact on the size of your nest egg. As the GAO has reported, a plan charging 1.5% annually is likely to return 17% less over 20 years than a plan that costs just 0.5% — a difference that can amount to a $100,000 or more for a typical retiree.

BrightScope CEO Mike Alfred says his company, which began rating plans last year, currently rates more than 30,000 401(k)s, which cover more than 50% of plan participants. Eventually BrightScope hopes to rate the majority of 401(k) plans in the country. …read more