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 the German replacement system, which was mostly based on replacement battalions ( Feldersatz-Bataillon). The idea was that each Wehrmacht and Waffen SS division would have a replacement battalion (sometimes some other formation) back home in Germany. This battalion would train replacements for the 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 the huge casualties in campaign against the Soviet Union. Therefore, often whole remnants of division would be pulled back and reconstituted, while leaving only small Kampfgruppe at the front (or none at all). One example would be the 3rd SS Panzer Division Totenkopf which suffered heavy losses in 1941 and 1942, so it had to be pulled back leaving a battalion sized Kampfgruppe in Demyansk pocket.
Therefore, as a rule, Germans would not recall fully manned and equipped divisions from the Eastern to the Western front. Usually, these were shattered formations that needed to be rebuild and then instead of going back to the East, they were sent to the West. One example would be the 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 the 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 the 1st Fallschirm-Panzer Division Hermann Göring, which was first earmarked for return to the Eastern front while reforming as a Panzer division, but it was diverted to Italy in 1943 while reforming as a Panzer division, and finally arriving on Eastern front in the Summer of 1944.
Anyway, as Allied invasion drew nearer, Germans redirected more and more units to France where those units replenished losses, trained and awaited the start of the action. Depending if you believe pro-Soviet or pro-Western sources, between 20-30% of German land forces was deployed in France. The majority still remained in the East until the end of the war, but from the 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.