I work in DE but live in PA. When I enter in the amount of my DE state taxes paid - I am only getting partial credit on the TT PA State return. Why?
PA only allows a credit "Up-to" what PA would have charged for the same income.
Since PA has a pretty low flat rate of ~3%, and DE uses a graduated rate up-to ~6.6%, its possible that the credit is being limited to the lower PA rate.
@SteamTrain is correct. Here is PA's rule on the "other state credit":
If you can claim a resident credit as described above, your credit is the lesser amount of:
--The tax due to the other state (as may be adjusted), OR
--The tax calculated using the PA classified taxable income that you earned, received or realized in the other state multiplied by the Pennsylvania tax rate of 3.07 percent (0.0307).