Individuals: Make a payment of your estimated tax for 2015 if you did not pay your income tax for the year through withholding (or did not pay enough in tax that way). Use Form 1040-ES. This is the final installment date for 2015 estimated tax. However, you don’t have to make this payment if you file your 2015 return and pay any tax due by February 1, 2016.

Employers: For Social Security, Medicare, withheld income tax, and nonpayroll withholding, deposit the tax for payments in December 2015 if the monthly rule applies.