Get your taxes done using TurboTax

Estimated tax payments are applied when paid, so you can have underpayment for earlier tax quarters of the year even if you end up with a refund overall.  Income is treated by default as being received evenly throughout  the year, so if more of your income was was received later in the year you might be able to reduce or eliminate the penalty by annualizing income on Schedule AI of Form 2210.