After the Battle of Kursk, Hitler called back a lot of his forces to defend against the British and American invasion. My question is how much of his forces did he call back from the Eastern front?
Germans gradually diverted more and more units to the West
To understand what was happening, we first must discuss German replacement system, which was mostly based on replacement battalions ( Feldersatz-Bataillon). Idea was that each Wehrmacht and Waffen SS would have replacement battalion (sometimes some other formation) back home in Germany. This battalion would train replacements for division at the front, and wounded soldiers returning from convalescence would also join it before returning to combat units. Sufficient to say that even in 1941 this system started to break up, i.e. replacement battalions could not cope with huge casualties in campaign against Soviet Union. Therefore, often whole remnants of division would be pulled back and reconstituted, while leaving only small Kampfgruppe at the front (or no one at all). One example would be 3rd SS Panzer Division Totenkopf which suffered heavy losses in 1941 and 1942, so it had to be pulled back leaving battalion sized Kampfgruppe in Demyansk pocket.
Therefore, as a rule, Germans would not recall fully manned and equipped divisions from Eastern to Western front. Usually, these were shattered formations that need to be rebuild and then instead of going back to East, they were sent to West. One example would be 1st SS Panzer Division Leibstandarte SS Adolf Hitler. After failure at Kursk and Allied landings in Sicily, LSSAH was moved immediately to Italy, but it left its heavy equipment to sister SS divisions to replenish losses. In Italy it participated in some anti-partisan operations, but mostly trained and received new equipment, before being shipped back to East in late 1943, where again sustained significant losses, left Kampfgruppe and moved to France where it prepared for Allied landings. Other example would be 1st Fallschirm-Panzer Division Hermann Göring, which was first earmarked for return to Eastern front while reforming as Panzer division, but it was diverted to Italy in 1943 while reforming as Panzer division, and finally arriving on Eastern front in summer of 1944.
Anyway, as Allied invasion drew nearer, Germans redirected more an more units to France where those units replenished losses, trained and awaited start of the action. Depending do you believe pro-Soviet or pro-Western sources, between 20-30% of German land forces was deployed in France. Majority still remained in the East until the end of the war, but from second half of 1943 Soviets did feel certain relief as increasing number of German divisions was not going back to the East.
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From Kursk: The answer is none. When the Allies attacked Sicily, the battle of Kursk was involving all the resources the Axis has put near the front. The Soviets then counterattacked, putting even more pressure.
From the eastern front: Some units were moved from the eastern front, but they came late for Sicily.
What came un Italia? The bulk of forces arriving to the Italian front came from the occupied territories, especially where a lot of troops were fighting guerrillas. It means that some Axis troops left Yougoslavia, but also White Russia, which can be considered as the rear of the Eastern front.