TaxVigWhat happens if I miss a quarterly payment?
If you did not pay enough tax during the year, through withholding or estimated payments, you may owe a penalty for underpayment of estimated tax (IRS Topic 306).
The penalty is figured separately for each due date, based on how many days each underpayment stayed unpaid (Form 2210 instructions). So a late payment still helps: paying sooner lowers the penalty for the payment you missed.
Most people avoid the penalty if they owe less than $1,000 after withholding and refundable credits, or paid at least 90% of this year's tax or 100% of last year's, whichever is smaller (IRS Topic 306). Form 2210 shows whether you owe it.
A calculator, not tax advice. Show this to your CPA. Compare both counting methods with your own totals.