What is Moses' death date?

Moses died on the seventh of Adar.

The Talmud proves this as follows:

In Deuteronomy 34:8 we read that the Jews mourned for thirty days following Moses' death in the Plains of Moab. This area borders Israel, just east of the Jordan River.

The book of Joshua begins with G‑d's command to bring the Jewish people across the Jordan River. G‑d specifies that they are to cross in three days time. This instruction was given immediately after Moses died, meaning at the earliest possible opportunity after his death. This would have been following the thirty days of mourning.

In Joshua 4:19 we are told that the Jews crossed the river on the tenth of Nissan. If we subtract the three days between the command and actual crossing, plus the thirty days of mourning, we find the date of Moses' passing is the seventh of Adar.

Incidentally, the seventh of Adar is also Moses' birthday. This we derive from what Moses said on the day of his death (Deuteronomy 31:2): "Today I am one hundred and twenty years old."

Malkie Janowski for Chabad.org