Today's 30-year fixed rate mortgage rate is markedly lower than what Freddie Mac's weekly survey says it is.

According to the group's Primary Mortgage Market Survey (PMMS) released Thursday, the average 30-year fixed mortgage rate rose 0.05 percentage points to 4.28 percent this week.

The survey fails to capture what happened to rates after the government ended its shutdown, and averted a breach of the U.S. Treasury's debt ceiling, however. Today's real mortgage rates are their lowest in 18 weeks.

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Freddie Mac : 30-Year Fixed Rate Rises To 4.28%

Freddie Mac's Primary Mortgage Market Market Survey (PMMS) is a weekly publication which lists the average U.S. mortgage rate for three conventional loan types --  the 30-year fixed, the 15-year fixed, and the 5-year ARM.

Survey results are polled from up to 125 banks nationwide, each of which reports its "going mortgage rate" plus the number of discount points required to lock that particular rate. Discount points are a one-time fee paid at closing.

Freddie Mac also asks its banks to make certain mortgage assumptions.

The first assumption Freddie Mac asks banks to make is that the mortgage applicant is making a purchase with a twenty percent downpayment without the use of secondary financing (e.g.; HELOC, piggyback loan). Larger downpayments are allowed and do no affect pricing.

The second assumption banks are asked to make is that the mortgage applicant is a "prime borrower". A prime borrower is one with excellent credit scores; with verifiable income and a low debt-to-income ratio; and, with plenty of money in the bank.

Lastly, the banks are told to assume a 30-day mortgage closing.

For applicants meeting the above criteria, Freddie Mac survey reports this week's mortgage rates as follows :

• 30-year fixed rate mortgage : 4.28% plus an accompanying 0.7 discount points
• 15-year fixed rate mortgage : 3.33% plus an accompanying 0.7 discount points
• 5-year adjustable rate mortgage : 3.07% plus an accompanying 0.4 discount points

For everyone else, expect rates to be higher. This group includes buyers of condominiums; buyers with low credit scores; and, homeowners refinancing via HARP 2.0.

Post-Shutdown, Mortgage Rates Plunge 

Freddie Mac reported mortgage rates rising this week. However, for borrowers shopping a mortgage today, you're likely seeing the opposite. Mortgage rates are actually dropping.

The reason Freddie Mac gets it wrong this week isn't really its fault. The government-backed group sends its survey to banks each Monday and asks for replies to be returned no later than Wednesday afternoon. 

According to Freddie, though, most replies are received by Tuesday morning which leaves two entire days between the "end" of the mortgage rates survey and the survey's final publish date.

This week, those two days were important ones -- the government ended its 16-day shutdown and Congress agreed to extend the U.S. Treasury's debt ceiling. Both moves instilled confidence in the U.S mortgage bond market and sparked a wave of demand which led mortgage rates south.

Rates are improved by about 0.125 percentage points since Wednesday, leaving the 30-year fixed rate mortgage at its lowest point in 18 weeks and the 15-year mortgage similarly low.

30-year rates could keep falling, too, eventually falling into the 3s.

Earlier this year, of course, mortgage rates were in the low-three percent range. This was for a combination of reasons including a weak labor market, a slow-to-grow U.S. economy, and a Federal Reserve bent on keeping mortgage rates low. 

Then, in May, with the economy showing signs of improvement, the Federal Reserve said it would look at ending its mortgage rate-suppressing program known as "QE3". This announcement took rates from an all-time low to a multi-year high.

Now, with the labor market softening again and the economy sure to show signs of a slowdown from the shutdown, the Federal Reserve is likely to keep QE3 in play for at least a few additional months. It's among the reasons why rates are so low today.

Have you seen today's mortgage rates? It's worth a second look.

Should You Lock Your Mortgage Rate Yet?

Today's mortgage rates are dropping -- despite what you heard from Freddie Mac. Rates have cut new multi-month lows and may soon pierce 4.00 percent.

Then again, maybe they won't. 

Like stocks, mortgage rates are unpredictable and subject to change. That rate you chose to "sleep on" may be gone by morning forever. There's just no way to know.

To be safe, take a look at today's live mortgage rates and see how they'll fit your budget. For many people, this could be the last chance to refinance. Rates are available online, for free, and with no obligation whatsoever.

Get an instant, personalized mortgage rate here.