Page "Manna" Paragraph 27

Exodus states that the Israelites consumed the manna for 40 years, starting from the fifteenth day of the second month ( Iyar 15 ), but that it then ceased to appear once they had reached a settled land, and once they had reached the borders of Canaan ( inhabited by the Canaanites ).

Form critics attribute this variation to the view that each expression of the manna ceasing derives from different lore ; the " settled land " is attributed to the Priestly tradition, and " Canaan's borders " to the Yahwist tradition, or to a hypothetical later redaction to synchronize the account with that of the Book of Joshua, which states that the manna ceased to appear on the day after the annual Passover festival ( Nisan 14 ), when the Israelites had reached Gilgal.

The duration from Iyar 15 to Nisan 14, taken literally, is 40 years less one month.