By Anna Isaac

U.S. stock futures posted gains Wednesday as investors awaited the Federal Reserve's latest views on economic growth and inflation prospects.

Futures tied to the S&P 500 rose 0.5%, suggesting that the broad gauge may open higher. Contracts tied to the Nasdaq Composite Index ticked up 0.5%. Both benchmarks are in negative territory for the month so far, with the Nasdaq down nearly 5% in September.

Investors are weighing the prospect of continued support from the central bank against further delays to a fiscal spending package expected from lawmakers. While the Fed isn't expected to change interest rates Wednesday, policy makers may revise closely watched economic and inflation projections.

"We're expecting to see an upgrade in the growth numbers for the U.S.," said Edward Park, deputy chief investment officer at Brooks Macdonald. "Last time, they were very bearish compared to what the market had been expecting."

The meeting is the Fed's first since forging a new framework governing how to conduct policy over the long run. Investors are eager to get more guidance on how changes will work in practice.

"There is room for market disappointment today if we don't get any further details," said Seema Shah, chief strategist at Principal Global Investors. "What is too long for inflation to be above 2%? How far above that does it need to go before they start tightening?"

Investors are also continuing to assess the prospects for additional government spending, with negotiations complicated by calculations surrounding prospects in the November elections. On Tuesday, House Speaker Nancy Pelosi said the chamber should remain in session until lawmakers can strike a bipartisan agreement on new coronavirus relief. White House adviser Jared Kushner said that any deal could be a ways off.

"The recent stronger economic data is convincing investors that the economy is standing on its own two feet," said Ms. Shah. "But if we get final confirmation that there'll be nothing before the election, then there might be a negative reaction from the market."

U.S. retail sales data for August, due at 8.30 a.m. ET, may also give investors a sense of consumers' confidence and the strength of the economic recovery. The figures are expected to show another rise in outlays across an array of categories, including electronics and food services.

Ahead of the opening bell in New York, shares of FedEx rose more than 10%. The delivery company posted the highest quarterly revenue in its history as the coronavirus pandemic spurred residential-shipment levels normally seen during the holiday season.

Facebook shares fell 1.4% in off-hours trading after The Wall Street Journal reported that the Federal Trade Commission was gearing up to file a possible antitrust lawsuit against the company, in a case that would challenge the company's dominant position in social media.

Overseas, the pan-continental Stoxx Europe 600 index rose 0.4%.

In Asia, major equity indexes ended the day on a mixed note. Japanese stocks edged higher thanks to gains in e-commerce and online-services stocks, sending the Nikkei 225 index up less than 0.1%. China's Shanghai Composite Index ticked down 0.4%.

In commodities, Brent crude, the international energy benchmark, rose around 2% to $41.38 a barrel after data showing that U.S. crude inventories unexpectedly declined. Hurricane Sally, expected to make landfall Wednesday, has curtailed offshore oil production in the Gulf of Mexico, and is likely to further hit U.S. supply.

In bond markets, the yield on the benchmark 10-year U.S. Treasury ticked down to 0.671%, from 0.678% Tuesday. Bond yields and prices move in opposite directions.

Write to Anna Isaac at anna.isaac@wsj.com