The payments of an ordinary annuity are paid at the end of the given period, while the payments of an annuity-due are paid at the beginning of the period. . To help remember this, keep in mind that an annuity due "starts with a payment due", so it's the one with a beginning-of-month payment.

Since the two annuities are identical except for this one period difference, you compute the PV and FV of the annuity due by multiplying the PV and FV of an ordinary annuity by one period of interest. Conversely, you compute the PV and FV of the ordinary annuity by dividing the PV and FV of an annuity-due by a month of interest.. To help remember this, an annuity-due pays earlier, so it's always worth more!