When preparing Form 2210 to calculate an underpayment penalty, by default your tax withholding is treated as having been withheld equally in each of the four tax quarters of the year. However, if you actually had a larger amount of tax withholding in earlier quarters than in late quarters, your underpayment penalty will likely be reduced or eliminated by treating the withholding as paid when withheld instead of treating it as paid in four equal payments throughout the year.
