As mortgage rates hover near historic lows, Americans are saving big on monthly mortgage payments. In the fourth quarter of 2012 alone, homeowners spent almost 37 percent less on the payments than they did in the years before the housing bubble, according to real estate tracking firm Zillow.

But this saving has a flip side: As home values rise, paychecks aren’t keeping up. So, while average monthly payments are down, buyers are purchasing homes with a bigger price tag. At the end of 2012, buyers bought homes that were three times their annual income, up from 2.6 times before the housing bubble.

The disparity is stark in high-priced areas such as San Jose, where home buyers are purchasing homes for seven times their yearly salary. Meanwhile, in Detroit, the purchase price is typically just 1.5 times a buyer’s salary.

Homes appear more affordable because low mortgage rates are painting a distorted picture of the market, said Stan Humphries, chief economist at Zillow.

The average rate for a 30-year fixed mortgage fell to 3.43 percent this week, compared with 3.88 percent a year ago, according to data released by mortgage giant Freddie Mac. That is not far from the historic low of 3.31 percent in November.

The home-price to annual-income ratio around the country.

“We’re in a carnival fun-house mirror,” Humphries said. When interest rates return to pre-crisis levels, between 6 and 8 percent, the illusion of affordability won’t last, he said.

Until that happens — and it is not likely this year — buyers will continue to flock into the market, Humphries said. That will push home prices higher, he said, and, with them, the price-to-income ratio.

In the Washington region, homeowners spent about 27 percent less per month on mortgage payments in 2012 than they did in the pre-bubble years of 1985 through 1999.

But the home price was typically 3.5 times their annual income, slightly above the national average. The figure was 2.7 times income in the pre-bubble years.

This comes as home prices in the Washington area reach a record high, according to recent data. The median sale price of a home in the District last month was $460,000, compared with $405,000 in March 2012.

Zillow predicts home values in the region will increase by an additional 1.9 percent in 2013.

Home buyers able to secure a low interest rate are lucky, but they should be aware of their limits, said Gabe del Rio, chief operating officer at Community HousingWorks, a nonprofit group in San Diego.

“It’s kind of like knowing your calories each day,” he said. “If you’re pushing that limit to the higher end, then you’ve also got to be very self-regulated.”