The amount to be withheld on a federal or state return is the amount that you estimate to be what you need to cover your taxes assessed.
Nobody knows what your actual tax at the end of the year will be, because you could have life changes or changes in income or there could even be law changes.
When you file the W-4 with your employer, the information you give tries to estimate a good amount for state withholding, but it is not perfect. For the federal return you have a Tax Withholding Estimator, but I don't know if any states have one.
Taxpayers generally have to look at the results for one year and make changes to their withholding for the next year to try to minimize the size of the refund or the tax due.
But the amount withheld is never the exact amount, except by luck.
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is all your income reported on a W-2? do you get paid the same every pay period? if not the way withholding is calculated can leave you overpaid or short. sometimes changes in the tax laws can affect your tax liability.