You misunderstood my original post. One extra payment per years means 13 mortgage payments, instead of 12. (Almost all US mortgages require monthly payments.)

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.