If you didn't pay enough tax throughout the year, either through withholding or by making estimated tax payments, you may have to pay a penalty for underpayment of estimated tax. Generally, most taxpayers will avoid this penalty if they either owe less than $1,000 in tax after subtracting their withholding and estimated tax payments, or if they paid at least 90% of the tax for the current year or 100% of the tax shown on the return for the prior year, whichever is smaller.
