If your only income reported on a PA resident income tax return is from W2 income, it is very common for your employer withheld exactly what your state income tax liability is on your income. Thus, your tax liability equals the taxes paid resulting in a zero balance. You also may have a zero balance if your income qualified you for the PA Tax Forgiven rate of 100%. See: https://www.revenue.pa.gov/FormsandPublications/FormsforIndividuals/PIT/Documents/rev-631.pdf
PA income tax law differs significantly from federal and it is not uncommon for a PA income tax return to show a zero balance.
