Soviet losses for the war are not precisely known, however the most accurate estimates are that at least 26 million died at the hands of the axis or whilst under their occupation. At least a further 4 million were lost to Soviet action, independent of German actions.
It is at least logical to suppose that more Soviet civilians were massacred as the Heer was being forced back out of German occupied territories. There is simply no way to precisely quantify these figures, but it is at least logical in understanding the patterns of losses sustained by the Soviet Union.
It is estimated that Soviet battle related fatalities amounted to 9 million men. Of these, more than 4 million perished in 1941, and another 2 million in 1942. Approximately 1.5 million Russian soldiers are believed to have died in 1943. One million are believed to have perished in the 1944 campaigns. About 500000 perished in the 1945 campaigns. These figures don't include wounded and don't include captured soldiers. The prisoner counts were generally reducing after 1941, with each year that passed. .
It is estimated that at 3.3 million Soviet POWs died in Nazi custody, out of 6.7 million that surrendered during the war. Overwhelmingly these surrenders occurred in 1941, with a leser number occurring in 1942. This casualty figure represents a total of 57% (after taking into account enforced drafts into the heer) of all Soviet POWs and may be contrasted with 8,300 out of 231,000 British and U.S. prisoners, or 3.6%. About 5% of the Soviet prisoners who died were Jews. The most deaths took place between June 1941 and January 1942, when the Germans killed an estimated 2.8 million Soviet POWs primarily through deliberate starvation, exposure and summary execution. It is estimated a further 1 million had been "released", most of whom were so-called Hilfswillage for (often compulsory) auxiliary service in the Wehrmacht, 500,000 had fled or were liberated, the remaining 3.3 million had perished as POWs. The Hilfswillage personnel that survived the war were nearly all killed on repatriation after the war. Judging by the experiences of my stepfather in 1942, many more Soviets than show in official figures wound up fighting in the heer. My stepfather, was a machine gunner . His, and every other heavy weapons unit in the division, had Russians assigned to various units. None of these were on strength "officially" until much later. We have no way of knowing how many of these unlawful draftees were killed
The figure of 3.3 million POW dead is based on German figures and analysis. Data published in Russia presents a slightly different view of their POW dead. Zemskov estimates Soviet POW deaths at 2.3 million, he published statistics that put Soviet POW losses at 2,471,000 (5,734,000 were captured, 821,000 were released for German military service, 72,000 escaped and 2,371,000 liberated ). Of the 823,000 POWS released for service in the German military forces 212,400 were killed or missing, 436,600 were returned to the USSR and then executed or worked to death. and 180,000 remained in western countries after the war.
Russian military historian Krivosheev maintains POW and MIA losses of the combat forces were actually 1.783 million, according to Krivosheev the higher figure of 3.3 million POW dead includes reservists not on active strength, civilians and military personnel reported missing who were recovered during the course of the war. I suspect the Soviet sources arer playing with the figures a bit.
By September 1941, the mortality rate among Soviet POWs was in the order of 1% per day. According to the US holocaust museum, by the winter of 1941, "starvation and disease resulted in mass death of unimaginable proportions". This deliberate starvation, despite food being available, led many desperate prisoners to resort to acts of cannibalism and was was partly Nazi policy and partly the result of underestimatiing the numbers of captured soldiers. The Germans did have an official policy designed to kill the Red Army PoWs by starvation, called the "Hunger Plan" developed by Reischminister Beck
Based on these figures, rough as they are, I cant see how Russian casualties in 1945 exceeded 1941, except if soldiers that were defenceless at the time of their loss (ie PoWs) are included in that mix.
As an aside, Axis prisoners held in Soviet captivity after the war also suffered, but the numbers lost are dwarfed by the losses inflicted by the Germans. The 1974 West German report into this placed the number (of all nationalities) in Russian custody at 3.1 million of which about 2.4 million were german. The west german report goes to say that about 1 million detainees perished (which includes those Hillswillage personnel). This German source says that by 1949, less than 100000 remained in custody, and that in 1946, more Germans were being held in custody by the british, than were held by the Russians. I personally find that last figure hard to believe.
Mosier as an author is generally not well regarded. He has been labelled a "contrarian" rather than "historian" and many of his claims are highly selective to the point of extreme bias. ive noit read him myself, but the reviews of his work are at best mixed