Primary Dates

STATE Filing
Deadline PRIMARY RUNOFF Presidential
Primary
ALABAMA 8-Nov-19 3-Mar 31-Mar 3-Mar
ALASKA 1-Jun 18-Aug 4-Apr
ARIZONA 6-Apr 4-Aug 17-Mar
ARKANSAS 12-Nov-19 3-Mar 31-Mar 3-Mar
CALIFORNIA 6-Dec-19 3-Mar 3-Mar
COLORADO 17-Mar 30-Jun 3-Mar
CONNECTICUT 9-Jun 11-Aug 28-Apr
DELAWARE 14-Jul 15-Sep 28-Apr
FLORIDA 24-Apr 18-Aug 17-Mar
GEORGIA 6-Mar 19-May 21-Jul 24-Mar
HAWAII 2-Jun 8-Aug 4-Apr
IDAHO 13-Mar 19-May 10-Mar
ILLINOIS 2-Dec-19 17-Mar 17-Mar
INDIANA 7-Feb 5-May 5-May
IOWA 13-Mar 2-Jun 3-Feb
KANSAS 1-Jun 4-Aug 2-May
KENTUCKY 10-Jan 19-May 19-May
LOUISIANA 17-Jul 3-Nov 5-Dec 4-Apr
MAINE 16-Mar 9-Jun 3-Mar
MARYLAND 24-Jan 28-Apr 28-Apr
MASSACHUSETTS 5-May 1-Sep 3-Mar
MICHIGAN 21-Apr 4-Aug 10-Mar
MINNESOTA 2-Jun 11-Aug 3-Mar
MISSISSIPPI 10-Jan 10-Mar 31-Mar 10-Mar
MISSOURI 31-Mar 4-Aug 10-Mar
MONTANA 9-Mar 2-Jun 2-Jun
NEBRASKA 2-Mar 12-May 12-May
NEVADA 13-Mar 9-Jun 22-Feb
NEW HAMPSHIRE 12-Jun 8-Sep 11-Feb
NEW JERSEY 30-Mar 2-Jun 2-Jun
NEW MEXICO 10-Mar 2-Jun 2-Jun
NEW YORK 2-Apr 23-Jun 28-Apr
NORTH CAROLINA 20-Dec-19 3-Mar 12-May 3-Mar
NORTH DAKOTA 6-Apr 9-Jun 10-Mar
OHIO 18-Dec-19 17-Mar 17-Mar
OKLAHOMA 10-Apr 30-Jun 25-Aug 3-Mar
OREGON 10-Mar 19-May 19-May
PENNSYLVANIA 18-Feb 28-Apr 28-Apr
RHODE ISLAND 24-Jun 8-Sep 28-Apr
SOUTH CAROLINA 30-Mar 9-Jun 23-Jun 29-Feb
SOUTH DAKOTA 31-Mar 2-Jun 11-Aug 2-Jun
TENNESSEE 2-Apr 6-Aug 3-Mar
TEXAS 9-Dec-19 3-Mar 26-May 3-Mar
UTAH 19-Mar 23-Jun 3-Mar
VERMONT 28-May 11-Aug 3-Mar
VIRGINIA 26-Mar 9-Jun 3-Mar
WASHINGTON 15-May 4-Aug 10-Mar
WEST VIRGINIA 25-Jan 12-May 12-May
WISCONSIN 1-Jun 11-Aug 7-Apr
WYOMING 29-May 18-Aug 4-Apr
Runoffs

Primary runoffs between the top two vote-getters may take place in some states if no candidate receives over a certain threshold of the vote in the primary:
30% in North Carolina (only if requested by the runner-up)
35% in South Dakota
50% in Alabama, Arkansas, Georgia, Louisiana, Mississippi, Oklahoma, South Carolina, and Texas.
Georgia conducts a general election runoff between the top two vote-getters for state races on Dec. 1 and for congressional races on Jan. 5, 2021, if no candidate receives a majority on Nov. 3.
Louisiana conducts a general election runoff between the top two vote-getters on Dec. 5 if no candidate receives a majority on Nov. 3.
Filing Deadlines

All filing deadlines on the calendar above are for major-party candidates and only apply to congressional and statewide races unless noted below. Independent and third-party candidates, or contests for other races (including the presidential race), may be subject to different deadlines.
Georgia’s filing deadline for the special Senate election is Sep. 4. 
California’s filing deadline is extended five days (to December 11, 2019) in races where no incumbents file for reelection.
Florida’s filing deadline for state candidates is June 19.
Massachusetts requires candidates to file with local election officials on May 5, then requires them to file again with the secretary of the commonwealth on June 2. The first step is therefore necessary but not sufficient for candidates to appear on the ballot.
Nebraska’s filing deadline for incumbents, regardless of whether they are seeking reelection or another office, is Feb. 18.
Conventions

Colorado, Connecticut, Massachusetts, New Mexico, New York, North Dakota, and Utah parties conduct conventions prior to their primaries that can impact primary ballot access.
Iowa parties conduct conventions to select nominees if no candidate receives over 35% of the vote in the primary.
Minnesota parties conduct conventions after which candidates who fail to win their party’s endorsement often (but by no means always) drop out.
Virginia parties, at their discretion, may select nominees at conventions rather than via primaries.
Sources: Green Papers, Run For Office, Frontloading HQ, state elections sites and statutes