<prompt> Human: Ive been looking into this as a first time home buyer and commonly people say that the money you put towards your mortgage principal is guaranteed return on your dollar which makes sense, but a lot say you can typically earn more saving for retirement. What Im getting stuck on is people keep saying the the return on your extra mortgage principle is equal to your Mortgage rate. So if I have a 4.5 rate then I 4.5 on every dollar extra I pay. But this seems very off to me. The way mortgages work being amortized the interest ends up being far more than 4.5 of the total amount.For instance a 200,000 mortgage with 4.5 interest for 30 years ends up costing 164,000 in interest total. And if you were to pay an additional 100 a month over the required payment you end up saving 40,000 in interest and paying off the mortgage in 23 years. That means you spent 27,600 and saved 40,000 which is much more than a 4.5 return.Im guessing Im just not understanding something or missing something big here. Any insight would be great.  <response>: If you put 100month in an account paying 4.5, after 23 years youd have about the 40k you said you saved by paying down the mortgage by that amount, proving the point that paying down the mtg yields a 4.5 return. 