For the last payment of the year you get a little extra time. Instead of being due December 15, it is due January 15. Again if it falls on a weekend or holiday there is a little extra time
This is the estimated tax schedule for tax year 2012. The last payment for estimated tax for 2012 is due on January 15, 2013.
1st installment April 17, 2012
2nd installment June 15, 2012
3rd installment Sept. 17, 2012
4th installment January 15, 2013
I am not a tax attorney, CPA or tax preparation specialist. The information here is meant as a general guide. For specific questions about your own taxes, please refer to IRS publications or consult a tax specialist.