Mortgage rates and the bond market have a nice little marriage; 9+ times out of 10, when bond rates rocket higher, fixed mortgage rates move up too.

As seen in the chart below, 5-year fixed rates and bond yields track each other fairly closely over time. In fact, on a monthly basis going back to 1980, there’s been a 97% correlation between the two.

It’s not a perfect marriage though, as we’ve seen recently.

On March 9, mortgage rates and the bond market unexpectedly kicked their relationship to the curb. Yields went way up, and mortgage rates actually fell slightly.

Banks are behind this pleasant divergence. In a rush for market share, they’ve started ‘buying’ customers with, what some say, are “unsustainably low” mortgage rates. (See “Banks Wage War”)

Put another way, big banks are pricing 5-year fixed mortgages at unusually low spreads above bond yields.

This is a party for homeowners. You don’t find 5-year terms at 70-85 basis points above the GOC very often.

Hopefully this “unsustainable” trend can be sustained well into the future. But odds are, spreads will normalize after the spring (at least until the banks decide to ‘give away’ mortgages once again).

This is far from the first time that fixed rates have drifted apart from bond yields. From late 2007 to mid 2009, spreads were way out of whack. The credit crisis kept mortgage rates high while bond yields dropped to multi-decade lows.

Everything needs to be put into perspective though. Despite deviations from the norm, the norm isn’t dead yet.  In general, lenders still need to pay bond rates for mortgage money, and they still have similar costs as before.

So when yields go one way, and fixed mortgage rates go the other, remember they’re still married. They’re just temporarily separated.

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Sidebar:  Speculating on long term rate direction is like flipping a coin. It’s almost certain you’ll be wrong as much as you’re right.

Yet, when you see a big move in yields, on a short-term basis, there’s usually predictive power there. 

This comes into play when you want to lock in a rate on a new mortgage.  If you see yields jump 1/4 point, for example, it’s usually worthwhile to move quickly and get a rate hold.  If you don’t, there’s a good chance you’ll pay a slightly higher rate. 

Paying a fraction of a percent more isn’t the world, but the extra interest does add up over five years.

Whenever we see yields move in big spurts, we write about it here. When you see these stories, it helps to remember:

• The short term isn’t the long term. If you read that rates may go up next week,” that’s a short term statement. Economic news could come out two weeks later and drive rates the other way.
• The relationship between bonds and mortgage rates isn’t perfect, and even short-term forecasts won’t always be accurate.

That said, over the long run you’ll be right far more than you’re wrong by assuming fixed rates will track bond yields.