December 1 – EmployersDuring December, ask employees whose withholding allowances will be different in 2021 to fill out a new Form W4 or Form W4(SP).December 15 – Social Security, Medicare and Withheld Income Tax If the monthly deposit rule applies, deposit the tax for payments in November.December 15 – Nonpayroll Withholding If the monthly deposit rule applies, deposit the tax for payments in November.December 15 – Corporations The fourth installment of estimated tax for 2020 calendar year corporations is due. December 31 – Last Day to Set Up a Keogh Account for 2020 If you are self-employed, December 31 is the last day to set up a Keogh Retirement Account if you plan to make a 2020 Contribution. If the institution where you plan to set up the account will not be open for business on the 31st, you will need to establish the plan before the 31st. Note: there are other options such as SEP plans that can be set up after the close of the year. Please call the office to discuss your options.December 31 – Caution! Last Day of the Year If the actions you wish to take cannot be completed on the 31st or a single day, you should consider taking action earlier than December 31st.