In the in-game Leaderboard panel, fourth tab, you will find your rank % which will indicate the league you are to go to, either drop the league or promote.

Sometimes this information can vary, as after the season ends and game enters maintenace mode, the system is designed to remove all inactive players from the leaderboard rank and recalculate the rank %.

To ensure you go to the league you aim for, take a buffer and add 1%-2% to your rank percentage and make sure you hit the destination.