<prompt> Human: Long time reader. First time poster. Im trying to figure out the following: If I have an extra 1, 10, 100 or 1000 at the end of a given month, what is the cost benefit of applying that money against my mortgage? In other words, what kind of return would I need to get on that extra 1, 10, 100 or 1000 in order to do better than simply putting it towards my mortgage? It seems that the answer to that question changes on a monthly basis as the ratio of interest-to-principle changes with every payment. Secondly, given that those extra dollars paid towards my mortgage lead to a guaranteed future savings e.g., if I put an extra 1000 against my mortgage every month, I could pay off my loan by Oct. 2023 and save 87,000 over the life of the loan: how does one quantify what I should hope to get for that same extra 1000 per month, if I choose an alternative investment? If you need specific details regarding my situation to answer this question, here they are: My wife and I purchased our home in March, 2012. We took a 256,000 30-year fixed mortgage at 3.75. We currently make 13 payments on our mortgage annually. We pay our mortgage monthly and every March make one extra payment. Here is an amortization schedule that describes our loan and payments: shorten link to bankrate.com with all those details already entered.Thank you in advance!EDIT: I just want to thank everyone for sharing their advice and thoughts. You are all very kind to give me some of your time and youve each influenced my thinking a lot. Have a wonderful holiday season.  <response>: It might be worth mentioning that an Extra 100 In the first year is gonna save you more than an extra 1000 in the 10th year. 