Most mortgage rates decreased to start the week by about 3 to 4 basis points (a basis point equals 1/100 of a percent), with two fairly drastic exceptions. The 30-year fixed jumbo loan skyrocketed 17 basis points to 4.63%. A jumbo mortgage is a loan for a minimum of $417,000, though that amount can increase in higher-cost areas.

The other rate exception was a whopping 15-basis-point drop in the 15-year fixed refinance loan, which more than erased the 0.14% increase borrowers endured on Friday.

Here are today's average mortgage rates across the U.S., along with where they stood a month ago.

Mortgage Type

Mortgage Rates Today

Mortgage Rates 1 Month Ago

30-year fixed jumbo

4.63%

4.40%

30-year fixed

3.94%

3.88%

15-year fixed

3.13%

3.08%

30-year fixed refinance

3.91%

3.88%

15-year fixed refinance

3.10%

3.09%

5/1 ARM

3.22%

3.12%

5/1 ARM refinance

3.31%

3.30%

Data source: Bloomberg. National average rates, which may include points.

Today's mortgage rates remain extremely attractive, but home shoppers just two years ago enjoyed some of the lowest rates ever. For some perspective, here are the average mortgage rates from way back in May 1997.

Mortgage Type

Mortgage Rates, May 2015

30-year fixed

3.84%

15-year fixed

3.06%

1-year ARM

2.49%

5/1 ARM

2.89%

Data source: Federal Home Loan Mortgage Corporation (Freddie Mac). Rates do not include points.

For existing homeowners looking for a home equity line of credit (HELOC) or equity loan, the strong housing market continues to swing in borrowers' favor. HELOC rates inched down to 5.27%, while equity loan rates held steady at 5.29%. Last month, HELOCs were at 5.24% and equity loans sat at 5.30%.