This app support 2 methods : (Principal & Interest) and (Interest Only).
In Principal and Interest tab which allow calculate the money extra payment per month to save interest and payoff earlier.
Principal and Interest tab :

Amortization:

Change unit:

Payoff early by :

Interest Only tab:

It is free and available on the iOS App Store
Link : https://itunes.apple.com/us/app/loancalc-early-payoff/id1097378421?mt=8&at=10l3Vy
In Principal and Interest tab which allow calculate the money extra payment per month to save interest and payoff earlier.
Principal and Interest tab :

Amortization:

Change unit:

Payoff early by :

Interest Only tab:

It is free and available on the iOS App Store
Link : https://itunes.apple.com/us/app/loancalc-early-payoff/id1097378421?mt=8&at=10l3Vy
