MOSCOW—Russia’s economy minister said Saturday that the country’s gross domestic product is expected to shrink by 3% in 2015 with oil prices at $50 a barrel and an estimated capital outflow at $115 billion, Russian news agencies reported.

The government previously predicted the decrease in GDP at 0.8%. Inflation in 2015 is now forecast to stand at 12%, up from the previous estimate of 7.5%, Alexei Ulyukayev said, Russian news agencies reported.

The announcement comes a day after the Russian central bank unexpectedly lowered its key interest rate by two percentage points, sending the ruble lower. Russia was also recently downgraded to “junk” level, below investment-grade, by the credit rating company Standard & Poor’s amid the mounting violence in eastern Ukraine.

Russia has previously warned that the country’s already ailing economy will slip into recession in 2015, tarnished by billions of dollars in capital outflow, falling oil prices and Western sanctions.

Saturday Mr. Ulyukayev presented the figures the government will use to revise previous forecasts and account for falling oil prices and the pressure of sanctions over Moscow’s annexation of Crimea in 2014 that cut Russia off from Western capital.