How long was Israel in Slavery?#

The Israelites were actually only in Egypt for 215 years. Joseph and his family moved to Egypt 215 years after the promise is given to Abram.

Different dates given#

Then the Lord said to Abram, “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for 400 years.” (Genesis 15:13)

The time that the people of Israel lived in Egypt was 430 years. At the end of 430 years, on that very day, all the hosts of the Lord went out from the land of Egypt. (Exodus 12:40–41)

And God spoke to this effect—that his offspring would be sojourners in a land belonging to others, who would enslave them and afflict them 400 years. (Acts 7:6)

Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ. This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void (Galatians 3:16–17)

Explanation

430 - From the promise given to Abram to the departure (to the day) was 430 years. The nations began with Abram. This is when Abram first lived in Egypt. God makes the promise to Abram and he leaves Haran. Genesis 12:2

Exo 12:41 And at the end of four hundred and thirty years, to the very day, all the hosts of the LORD went out from the land of Egypt.

400 - The “affliction” to the nation began when Ishmael, son of Hagar the Egyptian, mocked and persecuted Isaac. Genesis 21:9; Galatians 4:29