lolbini
This (from chicagoist) is teh rulez:

Today I signed a bunch of paperwork related to mortgages and talked with my lender about how mortgage rates are determined. As with just about everything that any professional field does, there really isn’t that much magic behind getting an approximate sense of how this works. Apparently if you want to know whether you can probably get a 1/8th % better rate on a 30-year fixed mortgage, you should watch the 10 year treasury note. Fixed rate mortgages tend to follow fluctuations in this. I’m guessing the magic threshold varies, but right now I’ve been told that if you witness a 0.070 change in price of this note then mortgage rates might follow suit (up or down, with the note). USNews has more on this. Obviously the tnote doesn’t strictly determine the mortgage rate, but if you look at tnote pricing going back to the 80’s when mortgage rates were 2-3 times higher than they are today, it’s interesting to see that this was also about 3-4 times higher then than it is now.