It is a lot of hassle to split $20 million to 200 accounts by yourself, hence the thriving of the business.

Ordinarily, savers' deposits are covered by the Federal Deposit Insurance Corp. for as much as $100,000 per depositor, per institution. Those who want to insure more than that would have to set up other types of accounts -- such as individual retirement accounts, joint accounts or revocable trust accounts -- or spread out their deposits across different banks. Savers who have uninsured deposits could be at risk of losing their money in a bank failure. About 36.3% of domestic deposits were uninsured as of the end of March, according to the FDIC.

Promontory breaks up large deposits into pieces of less than $100,000 and spreads the pieces among the more than 850 banks in its network. An individual with $1 million to deposit, for example, could take it to one of the banks in the network. Promontory would divide it into 11 CDs -- so each CD would have less than $100,000, allowing both principal and interest to be eligible for full FDIC coverage -- and then place them at member banks. To the customer, though, the deposit would look like one CD, with one interest rate, one bank statement and one 1099 tax form.