An annuity in the literal sense is a series of annual payments. More broadly it may be defined as a series of equal payments over equal intervals of time. A life annuity, a subclass of annuities in general, is one in which the payments are guaranteed for the lifetime of one or more individuals. A group annuity differs from an individual annuity in that the annuity payments are based upon the assumed length of lives of members of a given group. The size of the payments depends on several factors: the assumed interest rate, the life expectancy of the individual or of the individuals making up the group, the length of the period during which payments are guaranteed, the length of time elapsing before the payments begin, and the number of lives on which the payments are continued. For example, if payments to an annuitant aged 65 are to be guaranteed for 20 years, they will be substantially smaller than if they are guaranteed only for the remainder of the person’s life.

The typical group life annuity is sponsored by an employer, who may pay all or part of the cost. Under the usual arrangement, every employee receives each year a credit with the life insurance company for an annuity purchased to begin at age 65. The final pension received is made up of the sum of the individual annuities purchased throughout the worker’s life. As a rule, an irrevocable claim to these annuity rights is gained only after the person has worked with the employer for a given number of years or has reached a given age.

The basic advantage of an annuity is that it provides an income for life that is larger than the amount that the holder would receive by putting money out at simple interest. It is the reverse of life insurance, in that the insurer pays premiums to the insured; it resembles insurance in that the payment is based on life expectancy.

The problem of inflation has led to experimentation with variable annuities in order to protect annuitants against decreases in purchasing power. The major distinguishing characteristic of a variable annuity is that the payments vary according to underlying trends in the stock market. Funds paid in for the variable annuity are invested in common stock rather than in bonds, mortgages, or other fixed-interest investments as is true of regular annuities. In simplified terms, if the stock market rises 10 percent in one year, the annuitant may expect payments to go up by approximately 10 percent in the following year. Conversely, if the stock market drops 10 percent, the annuitant will suffer a 10 percent reduction in income. To the extent that the stock market reflects changes in the cost of living, the annuitant’s income is automatically adjusted for these changes each year; and, if the stock market also reflects increases in productivity in the economy, then the annuitant may expect to receive a share in such increases in the productivity as the economy may gain.

Some variable annuity plans are tied directly to a cost-of-living index. In order to finance the increased benefits, the employer invests a portion of the funds in equities such as common stock and real estate. An assumption is made that there will be a sufficient gain from this source to enable the employer to pay the increased cost of living, but the employee is not expected to suffer reductions in annuity payments.

The problem of adjusting retirement benefits to changes in the economy has been of concern in many countries. Some governments have pegged the price of government bonds to the cost-of-living index. Retired individuals purchasing government bonds may then receive automatic increases in interest payments if the cost of living rises. Their interest will not fall below a specified amount. Social security legislation in most parts of the world is geared in various ways to changes in the cost of living. In some cases benefits are directly tied to a price index. In other cases the legislature from time to time must be asked to make adjustments in social security benefits.