From season 11 to 12
The Ranked season officially ends on November 15 @ 11:59:59 PM your local server’s time zone. Rewards will be distributed within 4 weeks after the end of the season.
The Master, Grandmaster, and Challenger season ends November 15, 2021 11:44:59 PM local time.
Ranked decay will be turned off when the season ends.
From season 10 to 11
Season 10 ends on November 10th, 2020.
Rewards will be calculated based on your tier as of November 10th 00:00:01 AM in your local server time. If you decay, or get demoted, before the deadline, it will count.
Master and above will lock on November 9th 11:45 PM. Any game not completed before the ladder updates will not be counted.
League of Legends Season 11 starts on January 8.
From season 9 to 10
The Summoner’s Rift 2019 Ranked Season will end on November 19th. This could change if something weird happens; we’ll let you know if it does.
– RIOTIAMWALRUS – Designer at Riot Games
Patch 10.1 hits the live client on January 8th, and Ranked Season 10 will start a few days later, on January 10th, 2020.
From season 8 to 9
Ed “SapMagic” Altorfer (Riot Games lead designer on meta game systems) announced with a tweet the start of the preseason and of the 9th ranked season:
8.23 (Nov 21) – Preseason starts, gameplay changes.
8.24 – Ranked changes start to go out (tiers, placements).
9.1 – Mostly for stabilizing stuff.
9.2 (Jan 23) – The season starts.
Header image: Riot