The business model can be reduced to a simple equation:
Profit = earned premium + investment income - incurred loss - underwriting expenses.
Insurers make money in two ways:
- Through underwriting, the process by which insurers select the risks to insure and decide how much in premiums to charge for accepting those risks;
- By investing the premiums they collect from insured parties.
The most complicated aspect of the insurance business is the underwriting of policies. Using a wide assortment of data, insurers predict the likelihood that a claim will be made against their policies and price products accordingly. To this end, insurers use actuarial science to quantify the risks they are willing to assume and the premium they will charge to assume them. Data is analyzed to fairly accurately project the rate of future claims based on a given risk. Actuarial science uses statistics and probability to analyze the risks associated with the range of perils covered, and these scientific principles are used to determine an insurer's overall exposure. Upon termination of a given policy, the amount of premium collected and the investment gains thereon minus the amount paid out in claims is the insurer's underwriting profit on that policy. Of course, from the insurer's perspective, some policies are "winners" (i.e., the insurer pays out less in claims and expenses than it receives in premiums and investment income) and some are "losers" (i.e., the insurer pays out more in claims and expenses than it receives in premiums and investment income); insurance companies essentially use actuarial science to attempt to underwrite enough "winning" policies to pay out on the "losers" while still maintaining profitability.
An insurer's underwriting performance is measured in its combined ratio which is the ratio of losses and expenses to earned premiums. A combined ratio of less than 100 percent indicates underwriting profitability, while anything over 100 indicates an underwriting loss. A company with a combined ratio over 100% may nevertheless remain profitable due to investment earnings.
Insurance companies earn investment profits on “float”. “Float” or available reserve is the amount of money, at 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 the United States, the underwriting loss of property and casualty insurance companies was $142.3 billion in the five years ending 2003. But overall profit for the same period was $68.4 billion, as the result of float.
Some insurance industry insiders, most notably Hank Greenberg, do not believe that it is forever possible to sustain a profit from float without an underwriting profit as well, but this opinion is not universally held.
Naturally, the “float” method is difficult to carry out in an economically depressed period. Bear markets do cause insurers to shift away from investments and to toughen up their underwriting standards. So a poor economy generally means high insurance premiums. This tendency to swing between profitable and unprofitable periods over time is commonly known as the "underwriting" or insurance cycle.
Property and casualty insurers currently make the most money from their auto insurance line of business. Generally better statistics are available on auto losses and underwriting on this line of business has benefited greatly from advances in computing. Additionally, property losses in the United States, due to unpredictable natural catastrophes, have exacerbated this trend.