Mint, a free site that allows you to manage checking, savings and credit card accounts through an easy-to-use interface, will soon allow users to manage their investments, too.

There are plenty of investment-focused services out there, but Mint looks to be the first of the general personal finance sites to move beyond basic bank accounts and expenses into investment tracking.

The San Francisco startup says it will be compatible with 2,381 kinds of investment accounts. The company told us it plans to launch its new feature in private testing on May 6. In the meantime, TechCrunch has some early details worth pointing to.

Apparently, you’ll be able to manage brokerage, IRA, 401k and 529 accounts, but not mortgages or student loans (yet). It looks like the investment tools will be limited initially on helping you aggregate and navigate information from multiple accounts, but Mint plans to allow bill payments, stock trades and fund transfers in the future.

The focus seems a little more limited than other web investments companies we’ve covered, such as Cake Financial or Vestopia, which offer various kinds of social functionality. (Here’s a rundown of 11 such sites.) But by allowing users to manage even more of their financial life in one location, the new features should give Mint another leg up over competing personal finances sites like Wesabe, which don’t include your investments. That will be even truer once Mint moves beyond tracking, since it falls a little short if you still have to go elsewhere to pay your bills or make your trades.

Mint raised $12.1 million led by Benchmark Capital in March.

Patzer says the new features should help Mint expand beyond its core audience, which has been primarily users in their 20s who don’t have many long-term investments. Now, Mint can truly show you a complete picture of your net worth, including investments.

Patzer also clarified that adding data for more accounts (like student loans and mortgages) is the startup’s immediate priority. Enabling transactions such as bill payment is more of a long-term possibility.

Mint has set up a special site for VentureBeat readers to sign up for the private test. The test itself won’t go live until May 6, but users can start signing up now.