All readathons are (at least) a month long, except for the Christmas in July readathon (which may or may not happen, depending on the year).
Winter's Respite Readathon (#WintersRespite) - New month - always in February
Spring into Horror Readathon (#SpringHorror) - always in April.
Sci-Fi Summer Readathon (#SciFiJune) - always in June.
Christmas in July Readathon (#ChristmasinJuly) - Occasionally, not yearly
High Summer Readathon (#HSreadathon) - always in August (changed in 2019)
FrightFall Readathon (#FrightFall) - always in October.
Yuletide Spirit Readathon & Reading Challenge (#YuletideSpirit) - starts Thanksgiving week (U.S.) and runs for the entire holiday season. 2022 Dates: November 21, 2022 - January 6, 2023
Brought to you by True Book Addict, Castle Macabre and Christmas Spirit.