Brokerages may tout free trading as a major perk for investors to choose their platforms — but while they’re eliminating that stream of revenue, they’re making it up elsewhere, often at a cost to investors, according to news reports.

Discount brokerages such as Charles Schwab and TD Ameritrade — which announced plans for a $26 billion merger last month — now offer commission-free online trading on U.S.-listed stocks, ETFs and options.

But many online brokerages as well as wealth management firms are increasingly earning money off customer cash by putting it into lower-yielding deposit accounts instead of higher-yielding money market funds, Michael Wong, director of financial services equity research at Morningstar, tells The New York Times.

Schwab invests client cash at around 2.65% but pays investors just 0.06% to 0.45%, keeping the difference, according to the Times. Investors, meanwhile, can earn close to 2% on their cash by putting it elsewhere, the paper writes.

Net interest revenue, meanwhile, accounted for close to 60% of Schwab’s total revenue in 2018, and more than half of the revenue at TD Ameritrade and E-Trade, according to the Times.

Schwab makes money off of purportedly “free” services elsewhere as well, the paper writes.

For example, Schwab dropped the roughly 0.30% to 0.50% of a client’s assets charged by many robo-advisors, instead charging only the cost of the underlying funds on its robo platform, according to the Times. But Schwab digital investment advice clients must keep between 6% and 29% of their portfolio in cash, which pays 0.45%, a Schwab spokesman tells the paper.

Meanwhile, Schwab’s premium digital investment service, which also provides access to a certified financial planner, comes with a $25,000 minimum and costs $30 per month as well as a $300 fee up front, on top of the costs of investments, the Times writes.

Other brokerages, meanwhile, also receive “payment for order flow” from routing orders to market makers, and that’s likely to be an increased focus for companies offering free trading, William Trout, head of wealth management at research firm Celent, tells the paper.

“Free trading, or any other free service, should serve as a signal for investors — you’re probably paying somewhere,” the Times writes. “And part of the price you pay is figuring out how.”