While you now know that, in general, an annuity is an equal payment with
a finite number of payments, how do annuities work in the "real world"?
To give you an idea, check out Charles Schwab's annuity calculator.
Notice, the website shows three different payment options. The first
option, "For my lifetime (single life)", offers the highest payout per
period. Using a mortality table for annuities, the insurance company estimates the number of payments on the expected life of the annuitant.
If the annuitant outlives their expected life, payments are still made
until their demise. However, if someone signs up for this type of
annuity and dies immediately, no payments are made by the company. The
second option, "For my lifetime and someone else's lifetime (joint
life)", the number of payments are based on the expected number of
payments based on the expected life of both individuals named in the
contract. Again, if either party outlives their expected life, payments
are still made until both parties pass away. Finally, "A set period of
time (period certain)", the number of periods that payments will be made
is fixed when the annuity is first issued. The interest rate used by
annuity issuers in all cases is based of current market interest rates
when the annuity is first issued.