When you work with bullet operations, you have to know that from the first periodic amortization payment ( a₁ ) to the penultimate one ( a_s-1 ) you only pay coupons (only pay interest), because of that you have to use the following formula:

And the last periodic amortization payment ( a_s ) is used to pay interest and repayment of the principal ( C₀ ):

The only thing that need be considered is to always work with the effective rate of interest per time unit ( i^(m) ), because of that, if you do not enter this rate of interest, it is necessary to do the following conversion: