- December 16 – Due date for calendar-year corporations to pay the last installment of 2013 estimated income tax.
- December 31 – Deadline to complete 2013 tax-free gifts of up to $14,000 per recipient.
- December 31 – Deadline for paying expenses you want to be able to deduct on your 2013 income tax return.
- December 31 – Deadline for taking 2013 required minimum distributions (RMDs).