Correction amount = A-(B + C-D)
Where:
A = the amount of chapter 1 tax that would have been imposed had the items as adjusted been properly reported on the return for the first affected year;
B = the amount shown as chapter 1 tax on the return for the first affected year (taking into account amended returns);
C = amounts previously assessed or collected; and
D = the amount of rebates made.
Correction amount = A-(B + C-D)
Where:
A = the amount of chapter 1 tax that would have been imposed for the intervening year;
B = the amount shown as chapter 1 tax on the return for the intervening year (taking into account amended returns);
C = amounts previously assessed or collected; and
D = the amount of rebates made.
26 C.F.R. §301.6226-3