[thelastgallon]

>For example, if you make one extra payment per year, you will shorten a 30 year fixed rate mortgage by about 4.5 years.

This doesn't sound right. If I make 5 extra payments (either in 1 year or over 4 years), the mortgage will be shortened by 5 x 4.5 years = 22 years. I'm sure everyone would do this, 5 extra payments is super easy!

[throwaway2037]

You misunderstood my original post. One extra payment per years means 13 mortgage payments, instead of 12. (Almost all US mortgages require monthly payments.) To be clear: This extra payment is strictly optional, but it used to demonstrate how curtailment can meaningfully reduce the life of your loan and the amount of interest paid.