Web/iOS/Android: Most mortgage calculators will tell you how much your monthly payment will be or even how much total interest you'll pay each month compared to the principal. This calculator shows you that, but it includes more detailed information on how much you'll pay over time, too.
Enter your mortgage details and loan terms, and the tool will give you a chart on just about everything you need to get a clear idea of what it will cost to own your home over time.
For example, you'll see how much you'll pay in interest (which can add up to be hundreds of thousands of dollars on top of your principal) over the years. You'll also get an amortization graph and an annual table that shows how much you'll pay each year in interest, principal, and how those payments will reduce your monthly balance. What's more, you can adjust each field to see how much these numbers change if you change the terms.
The tool is free to use, and probably easiest on its web app, although you can also use it for mobile at the links below.
Karl's Mortgage Calculator [Apple Store]
Karl's Mortgage Calculator [Google Play]