Keep in mind that, unless you received a large portion of your income in Q4 and annualize income on Schedule AI (Form 2210), you'll likely still have underpayments for the first three tax quarters of the year. A Q4 estimated tax payment will not make up for underpayment for earlier quarters, although it will limit the interest and penalties going forward form the time of the payment. The quarterly required payments are determined by your quarterly income and your previous year's tax liability. Your income is treated as having been received evenly throughout the year unless you annualize on Schedule AI.
