There's a saying that you have to spend money to make money, and a recent report by the real estate site Zillow suggests this is particularly true of real estate. While many homeowners have built up a considerable amount of equity and will receive a handsome sum upon a sale, the typical seller also has to spend a hefty amount of money in the process.

In its 2019 Hidden Costs of Selling analysis, conducted in partnership with the home improvement resource Thumbtack, Zillow determined that sellers spent an average of $20,851 when listing their home. These expenses included costs such as sales commissions, closing costs, and renovations completed prior to the sale.

This amount is equal to about 9.2 percent of the median home value of $225,600 in February. Zillow said the costs can come as an unexpected and unpleasant surprise for sellers, particularly those who are listing a home for the first time.

"Selling is often a complicated process that can sometimes require extensive prep work in order to put your best foot forward for a successful sale," said Skylar Olsen, director of economic research for Zillow. "It also comes with huge transaction costs that aren't necessarily top of mind to someone who hasn't sold a home in a while or never has had the pleasure. Selling was hard even in the sellers' market of recent years, and it's going to get harder as markets soften."

More than two-thirds of the typical selling costs—$14,281—went to real estate commissions and transfer or sales taxes. The remaining $6,570 was the result of home preparation and local moving costs.

Selling costs varied strongly based on the market. In San Jose, Calif., the median home value of $1.2 million resulted in an average sales expense of $76,015, including $74,646 going toward commissions and closing costs. St. Louis, Mo., had the cheapest selling costs at $13,704, including $10,014 for commissions and closing costs. Home preparation costs were less variable, ranging from $3,690 in St. Louis to $7,840 in Sacramento, Calif.

According to the recent Zillow Group Consumer Housing Trends Report, nearly eight out of 10 sellers complete at least one home improvement before putting their residence on the market. Twenty-two percent of sellers who completed this work sold their home for more than their asking price, compared to 16 percent who weren't able to sell their home above list price.

Painting accounted for the bulk of home preparation costs, with the typical seller paying $2,600 for exterior painting and $1,245 for interior painting. This was followed by average costs of $1,805 in home staging expenses, $160 for house cleaning, $145 for full service lawn care, and $140 for carpet cleaning. Local moving costs typically came to $475.

"While the costs of these touch-up projects can add up, particularly in high cost-of-living metros, sellers should remember that by taking care of these projects, they can get a really strong return on their investment and may be more likely to sell their home for the highest possible price," said Lucas Puente, economist at Thumbtack. "As a first step, homeowners considering selling their home in the next 12 months should start doing research and budgeting appropriately to give themselves ample prep time."

Zillow calculated selling expenses by applying transfer taxes and a 6 percent commission to the median home value of each metro area it analyzed. The costs did not include expenses such as title insurance and filing fees. Thumbtack analyzed tens of thousands of quotes from small business professionals across the United States, determining the average cost for the seven home preparation steps considered to be the most popular among sellers.