Private Money loan early payoff?

[Brian Lepo]

I have a private money loan on one of my rentals that I would like to start making double payments on.  The loan is structured with no early payment penalty and the application of payments as follows:

All payments shall first be applied to interest and then to principal.  Interest will be calculated on the unpaid principal to the date of each installment payment and the payment made credited to the discharge of interest accrued and the balance to the reduction of principal.

If I were to start making double payments on this note is there a tool that will recalculate the "interest accrued" monthly as the principal is reduced?  Or am i over thinking this?