<prompt> Human: Im always trying to break even when I file my income taxes Ill owe 150 this year, but I know Ive heard that if you owe too much the IRS will slap on a fee. Is the fee a set amount, or is it a percentage of your income? And most importantly, when does the fee kick in?  <response>: Is the fee a set amount, or is it a percentage of your income?Its a somewhat complicated formula, explained in the instructions for IRS form 2210 PDFAnd most importantly, when does the fee kick in?From this IRS pageGenerally, most taxpayers will avoid this penalty if they owe less than 1,000 in tax after subtracting their withholdings and credits, 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. 