John Newton wrote 6 stanzas. They first appeared in the hymnbook, Onley Hymns in 1779. It was written to be sung at New Years, and was originally titled, "Faith's Review and Expectation", being the thoughts of an aged man looking back on a life of God's grace. Oddly enough, three of Newton's stanzas are commonly omitted from American usage and the last stanza that is usually included is NOT by Newton.   It first appears in print as the concluding stanza of Amazing Grace in Harriet Beecher Stowe's anti-slavery novel as a folk addition, sung around the campfire.
The commonly missing stanzas:
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The Lord has promised good to me,
His word my hope secures;
He will my shield and portion be,
As long as life endures.

Yea when this heart and flesh shall fail,
and mortal life shall cease;
I shall possess within the vail,
A life of joy and peace.

The earth shall soon dissolve like snow,
The sun forbear to shine;
But God who called me here below,
Will be forever mine.
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The "Day Is Past and Gone" lyrics have been reworked and appear as the following:

Christ Jesus is my Shepherd King,
Who ransoms from the fall;
I'll be clothed with His righteousness,
When death disrobes us all.