The earliest state primaries for 2020 are held March 3 and the latest in mid-September. June and August are the busiest months for state primaries.
| Alabama | March 3 primary |
| Alaska | April 4 (D) party-run primary, none (R) |
| Arizona | March 17 primary (D), none (R) |
| Arkansas | March 3 primary |
| California | March 3 primary |
| Colorado | March 3 primary |
| Connecticut | April 28 primary |
| Delaware | April 28 primary |
| Florida | March 17 primary |
| Georgia | March 24 primary |
| Hawaii | April 4 (D) party-run primary, March 10 (R) caucus |
| Idaho | March 10 primary |
| Illinois | March 17 primary |
| Indiana | May 5 primary |
| Iowa | Feb. 3 caucuses (both parties) |
| Kansas | May 2 (D) party-run primary, none (R) |
| Kentucky | May 19 (D) primary, March 21* (R) caucus |
| Louisiana | April 4 primary |
| Maine | March 3 primary |
| Maryland | April 28 primary |
| Massachusetts | March 3 primary |
| Michigan | March 10 primary |
| Minnesota | March 3 primary |
| Mississippi | March 10 primary |
| Missouri | March 10 primary |
| Montana | June 2 primary |
| Nebraska | May 12 primary |
| Nevada | Feb. 22 (D) caucus, none (R) |
| New Hampshire | Feb. 11 primary |
| New Jersey | June 2 primary |
| New Mexico | June 2 primary |
| New York | April 28 primary |
| North Carolina | March 3 primary |
| North Dakota | March 10 (D) party-run primary, TBD (R) caucus |
| Ohio | March 17 primary |
| Oklahoma | March 3 primary |
| Oregon | May 19 primary |
| Pennsylvania | April 28 primary |
| Rhode Island | April 28 primary |
| South Carolina | Feb. 29 (D) primary, none (R) |
| South Dakota | June 2 primary |
| Tennessee | March 3 primary |
| Texas | March 3 primary |
| Utah | March 3 primary |
| Vermont | March 3 primary |
| Virginia | March 3 primary (D), none (R) |
| Washington | March 10 primary |
| West Virginia | May 12 primary |
| Wisconsin | April 7 primary |
| Wyoming | April 4 caucus, (R) TBD |