Lower-income homeowners in the Boston area spend nearly twice as much of their income on mortgage payments as the average American, and a far-greater share than more affluent households in the region as well, according to a new study.

The report, released on Monday by real estate website Zillow, is another way of looking at how the high cost and low supply of housing in Greater Boston squeeze lower- and middle-income households. Zillow economists estimated that the lower-earning third of households — with annual incomes of roughly $35,000 or less, according to Census data — would need to spend 44 percent of their income to make mortgage payments on the average lower-priced home in Boston.

That’s compared with 23 percent among lower-income households nationally and the 16 percent that top-tier earners, those that earn about $100,000 or more, in the Boston area need to afford higher-priced homes.

“Housing affordability is a different story for low-income Americans than for median and high-earning people,’’ said Zillow chief economist Svenja Gudell. “They are spending much more of their income on housing, even when they buy the least expensive homes.’’

And they often have fewer homes to choose from.

Inventory in recent months has plunged in the bottom third of the market as buyers have snapped up what is available. In April there were 36 percent fewer homes listed for sale in the bottom third of the market — with a median price of $245,000 — than there were in the top third — with a median of $671,000 — according to Zillow data.

High prices, tight inventory, and pricey rents that make saving for a down payment hard effectively shut many families out of homebuying, despite record-low interest rates. And with prices continuing here to trend upward, there’s little sign of that changing any time soon.

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.