An annuity in advance is a series of payments that are due at the beginning of each successive time period. An example is a monthly rental payment on a property, which is usually due at the start of the period for which the rent is intended.
Another form of annuity is the annuity in arrears, where payment is due at the end of each successive time period. The present value of an annuity in advance is always higher than an annuity in arrears, since cash flows occur sooner.
An annuity in advance is also known as an annuity due.