Stocks rose slightly Wednesday as Wall Street anticipated the first Federal Reserve interest rate cut in four years. Gains were muted as uncertainty lingered over how big the easing will be from the central bank.

The Fed is expected to deliver its latest policy decision at 2 p.m. ET. The central bank is expected to lower rates by at least a quarter percentage point, but traders are divided over how big the reduction will be. CME Group ’ s FedWatch tool shows traders pricing in a 65% chance of a half-point cut and 35% odds of a quarter-point move.

It ’ s unusual to have this much uncertainty into a Fed decision as the central bank typically tries to telegraph its next move to the markets. Traders had believed for most of the last month that the Fed would lower by a quarter point, but the idea of a super-sized cut began to gain traction in the past week.

"You ’ d have to go back over 15 years to find such an uncertain situation this close to the decision. A lot of money will be made and lost today," Jim Reid, Deutsche Bank head of global economics and thematic research, wrote in a Wednesday note.

The ushering in of a cutting cycle is expected to shore up a stalling economy and further boost an already strong market, with the S&P 500 at a record following an 18% gain this year. History shows the benchmark averaged gains of about 16% in the 12 months following the first Fed rate cut in a cycle, according to data from Canaccord Genuity.