While I concur that we'll see extended 4.xx rates for some time, it's important to know a few things about mortgage rates as you look for a deal to close on:
1) "The Bottom" was in Q1 2009. Lenders priced a 4.125% sub $417k loan at about 1.0 point. We are approaching the bottom pretty quickly.
2) That 4.125% rate lasted for about 48 hours. During the next few months rates floated back above 5% and stayed there through the fall. Change comes quickly so if you are trying to get the deal of the century, you need to be nimble.
3) If the cost of money is roughly 1.0% (Zero rate, plus overhead), if the cost of servicing is 1.0%, and if the cost to manufacture the loan is 1.0% (3% total) you'll have to believe that investors are going to be willing to accept a 2.0% or less ROI for a mortgage at 4.0%. This assumes zero inflation and 100% payment of the mortgage backed security by all homeowners. What does this mean? 30 fixed rates below 4% are not likely. Note, not impossible, or never, just not likely.
If you can get a rate in the sub 4.5% rate range, lock it and don't look back. If you want to try and time the market, or hope that rates go below that threshold, you're playing with fire and need to be careful.
My .02c
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