As Mayor Lori Lightfoot prepares to unveil a new city budget that could include yet another big property tax hike, a new study out today underlines what Chicago homeowners already know in their bones: Little by little, city tax rates are catching up with those in the suburbs.

Chicago residents have long benefited from relatively low property taxes compared to the collar counties and even Cook County suburbs, with the city’s huge stock of tax-producing commercial property downtown carrying a disproportionate share of the load.

But that relative advantage has steadily melted away over the past decade amid rising taxes, even with lots of new commercial construction in the central area of the city, according to the Civic Federation study of effective tax rates.

For instance, average taxes on non-rental residential property in Chicago rose 2.5 percent in 2017 (the latest year for which complete figures are available) over 2016, moving from 1.69 percent to 1.74 percent of a property’s market value, the study said. But in that year, average taxes rose less or dropped in nine of the 11 Cook County suburbs studied—i.e., negative 1 percent in Schaumburg and negative 8.5 percent in Oak Park. Almost all communities studied in Lake, DuPage and Kane counties also showed a drop or less of an increase than Chicago’s in the effective tax rate on residential property, the report said.

The same is true over the past decade.