Although inflation expectations are the primary factor that influence the direction of mortgage rates on a day-to-day basis the stock market can also have an impact.
To understand how this relationship works it's first important to understand how mortgage rates are determined. Mortgage rates are entirely determined by the price of mortgage-backed bonds (MBS's). MBS's are bonds that are issued by Fannie Mae & Freddie Mac that are backed by the interest paid by mortgage holders. Like the stock market there is an exchange where MBS's are traded.
There is an inverse relationship between the price of MBS's and mortgage rates. When the price of MBS's increase mortgage rates drop and vice versa.
So, to understand how the stock market can influence mortgage rates we have to understand how they impact the price of bonds. Stocks and bonds compete for the same investment dollar. In other words, an investor with money to invest has to make a decision to invest their money in either the stock market or in the bond market (it should be noted that there are other investment options but these two classes are the primary vehicles for investment capital).
For an investor stocks are generally thought to provide higher returns over time but also come with greater volatility. Conversely, bonds tend to have lower returns over time but have less volatility. Because bonds tend to provide low volatility with modest returns the bond market can often act as a "safe-haven" for investors who sell their stock positions.
Therefore, in general, when the stock market goes down it is a sign that investors are selling stocks and shifting their capital into bonds. This boosts bond prices and drives mortgage rates down. Conversely, when the stock market rallies it is a sign that investors are selling bond positions in order to shift capital into the stock market. The greater supply of bonds on the market drives prices lower and pushes mortgage rates higher.
It's important to understand that there are a myriad of factors that impact mortgage rates on a day-to-day basis. Inflation expectations & technical trading patterns are two of the primary factors that we monitor. However, in the absence of new information on these two topics it's not uncommon for mortgage rates to be impacted by the stock market in the aforementioned manner.
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