On line 8 of the D-40, is the an amount that represents the amount of income that you earned while in Pennsylvania? The amount will be subtracted from federal income plus any additions (line 7), to give you DC adjusted gross income (line15).
Note that in the DC interview, you will see the screen "Subtractions from Federal Income, Part-year". Here you will be asked for the amount of income that you received while residing outside of DC. The amount you enter here will appear on line 8 on the D-40, so that DC will not tax you on this amount.
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