Mortgage Rates below 4% Again?

With the ten year yield falling slightly today to under 2.3%, how much would the ten year need to rally to have mortgage rates fall under 4% again?

With the ten year at 2.29% today, and based on an historical relationship, 30-year rates should currently be around 4.2%. 

As of this morning, Mortgage News Daily reports that 30 year fixed rate mortgages are around 4.1%. Pretty close to expected.

The graph shows the relationship between the monthly 10 year Treasury Yield and 30 year mortgage rates from the Freddie Mac survey.

Currently the 10 year Treasury yield is at 2.29%, and 30 year mortgage rates were at 4.1% according to the Freddie Mac survey last week.

Based on the historical relationship, the ten year yield would have to fall to around 2.1% for 30 year fixed mortgage rates to be at or below 4%.