The table below shows key 2021 deadline dates for filing 2020 tax returns and requesting temporary extensions. Given the number of missing government payments around the COVID relief economic stimulus payments and especially the dependent child stimulus payment, I expect there to a keen interest in the upcoming tax season. Especially for those expecting a large refund (see expected 2020-2021 tax refund schedule).

Tax Filing Deadlines	Tax Related Activity
January 1	First day to file a federal tax return, though the IRS generally will not accept e-file and free file returns until the date below. Even paper based filings won't be processed till later in the month
January 25	IRS E-file to go live, allowing submission of electronic tax returns for the vast majority of tax filers. Paper tax returns will begin processing later in mid-February as IRS system updates continue (IRS recommends e-filing for faster refunds)
February 12	Date by which you should have received a W-2 from employers you worked for during the tax year. If not, contact their HR/Payroll department to resend tax documents
February 12	Deadline for 1099 statements (factors in your AGI income) that report non-employee compensation, bank interest, dividends and distributions from a retirement plan. This date is also the deadline for self-employed individuals to file and pay in full their fourth-quarter estimated tax payment
February 22	Financial institutions (e.g Vanguard, Fidelity) must mail out 1099-B, 1099-S and 1099-MISC forms by this date. See what these forms are and if you will need one for your return
March 15	S Corporation and Partnership tax returns due
April 15	*Tax Day* Last day for filing federal and state income tax returns and extension requests.
April 15	Deadline for filing state income tax returns (for most states) and extension requests. Last day to make a contribution to a Traditional or Roth IRA, Health Savings Account (HSA), SEP-IRA or 401(k)
April 15	FBAR (Foreign Bank Account Report) forms due for taxpayers who have signature authority over $10,000 in total in foreign bank accounts in the prior year. Laws enacted last year change the standard FBAR due date to "tax day" (vs June 30th as in years past). No extensions are allowed and forms must be filed electronically.
September 15	U.S. citizens or resident aliens living abroad must file tax returns and pay any taxes due by this date (or file for a four-month extension)
October 15	Filing approved extended federal, state and S-Corp/Partnership income tax returns Note: you still need to file for an extension request by April 15th