U.S. stock index futures extended gains on Tuesday as cooler-than-expected inflation data bolstered expectations that the Federal Reserve is done with its interest rate-hiking campaign.

The Labor Department's report showed the consumer price index (CPI) rose 3.2% on an annual basis, compared to expectations of a 3.3% increase, according to economists polled by Reuters.

Core CPI, which excludes volatile food and energy costs, grew 4% year-on-year compared with forecasts of a 4.1% increase.

At 8:31 a.m. ET, Dow e-minis were up 327 points, or 0.95%, S&P 500 e-minis were up 55.5 points, or 1.25%, and Nasdaq 100 e-minis were up 249.5 points, or 1.6%.

(Reporting by Amruta Khandekar; Editing by Saumyadeb Chakrabarty)