I had a 30 year mortgage on one of my rental properties that I purchased in 2002. By adding $100 a month to each payment I paid off this property in less than 15 years. Now there is a formula one can use in an Excel spreadsheet that allows you to "plug in" values such as payment period, amount, interest rate and loan term. It will show you how long it will take to pay off a mortgage by changing the monthly payment (or whatever the payment period is, if not monthly.)
Now on the attached Excel spreadsheet I've set it up for monthly payments using the same formula that banks use to figure interest rate based on your outstanding balance each month.. In the first line of figure (line 3 on the attached) you can change the figures in columns A, B and C of row 3 with whatever your loan amount is, the monthly payment, and the Interest rate. You can change your monthly payment to see what difference it will make on your time to pay off the loan. The items you can change are in bold print. The sheet is password protected so that you can only change the variables and not accidentally mess up the formula. But if you want to play with it, I've set the password on this uploaded copy to "password" (without the quotation marks) so you can unprotect it if desired.