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annuity
annuity(number1, number2)
where number1 represents the interest rate (expressed as a decimal) and number2 represents the number of periods over which you receive annuity payments.
Value returned: the total cost of an annuity now that will pay you one unit per period over the specified number of periods, or a number equal to (1 - (1 + rate) ^ -periods) / rate
An interest rate involves a certain percentage (expressed as a decimal) per some unit of time—usually per year. You must use the same unit of time to measure the number of periods.
For example, if you have a yearly percentage rate but your annuity pays you monthly, use rate / 12, and be sure to express the number of periods as months (2 years = 24 months).
