In this scenario we take the payment in Scenario 2 - $632.41/month base payment and $300.00/month additional principal payment and switch to bi-weekly payments of $291.68 with an additional principal payment of $150.00 {this is an additional payment of $300/yr over Scenario 2} The result is the effective amortization is reduced to 16.62 years and the total interest paid is reduced by $37,212.60 (47.9%)