Russia has suffered about 325,000 deaths since February 2022, the Center for Strategic and International Studies (CSIS) said in its report.
The think tank said no major power has incurred casualties on this scale in any conflict since World War II.
Despite Moscow’s claims of battlefield momentum, Russia is paying an "extraordinary price" for limited territorial gains and is declining as a major power, the report said.
Russian casualties significantly exceed Ukrainian losses, according to the study. Ukrainian forces are estimated to have suffered between 500,000 and 600,000 casualties and between 100,000 and 140,000 deaths, the report said.
At current rates, combined Russian and Ukrainian casualties could reach 2 million by the spring of 2026, it added.
The report said that after seizing the initiative in 2024, Russian forces advanced at an average pace of 15 to 70 metres a day in their main offensives— slower than nearly any major offensive campaign in the past century.