It’s a cool tool, but I don’t see a way for it to show what the effect of making overpayments. Here’s one in Excel that does. The units are in GBP but it doesn’t really matter. Download the spreadsheet, plug in the numbers for your current mortgage, and then try typing in various recurring overpayment amounts to see how much it will shorten the life of your loan and how much you’ll save in interest.
For example, even a meager $50 overpayment will shorten a $300k / 5% / 30y mortgage by almost two years. $250 will take about 7.5 years off.
