Insurance companies earn investment profits on "float". Float, or available reserve, is the amount of money on hand at any given moment that an insurer has collected in insurance premiums but has not paid out in claims. Insurers start investing insurance premiums as soon as they are collected and continue to earn interest or other income on them until claims are paid out. The Association of British Insurers (gathering 400 insurance companies and 94% of UK insurance services) has almost 20% of the investments in the London Stock Exchange. In 2007, U.S. industry profits from float totaled $58 billion. In a 2009 letter to investors, Warren Buffett wrote, "we were paid $2.8 billion to hold our float in 2008."
Auto insurance premiums depend on the insured party's driving record. A record free of accidents or serious traffic violations typically results in a lower premium. Drivers with histories of accidents or serious traffic violations may pay higher premiums. Likewise, because mature drivers tend to have fewer accidents than less-experienced drivers, insurers typically charge more for drivers below age 25.