As in many other esports titles, League of Legends has a ranked system to measure yourself against your equal opponents. In order to assign your account to a league at the beginning, you must first complete ten games, after which you will receive a rank for the first time. The nine ranks in League of Legends are represented by the so-called ranked armor. The ladder ranges from iron league to challenger:
Each league is further broken down into four divisions, while division IV being the lowest and division I the highest. Only when you have played through all the divisions of a league you get into division IV of the next higher league.
Before you are placed into a league, you must first play 10 ranked matches. Only then your rank will be displayed. After the first game your rank will be displayed for you, in the next nine games you can then improve the rank until you have finally qualified for a league.
Which league you start in after the first game depends on your rank last season. New accounts that have never played ranked matches before start in the bronze league.
Promotion and Demotion (Promo Series)
To climb up from one division to the next, you have to collect LP (league points). Every game you win gives you LP for your rank, every game you lose, LP is substracted. How many League Points you get or lose per game depends on your MMR (more on that later). This means that the LP per game can vary from -20 to +30. With a balanced MMR, you get +20 LP for a win and -20 LP for losing.
Since preseason 11 there are no more promo series for divisions within a league. This means that once you would get more than 100 LP, you advance to the next rank. The excess league points will be credited to you for your new division. As soon as you fall back to 0LP, you can relegate.
If you reach 100 LP in division I of a league, you play for promotion in 5 games. Then you have to win three of the next five games to be promoted to the next league.
After you have been successfully promoted, your rank changes for example from Gold I to Platinum IV. In the new league you start again with 0 LP and fight for promotion to the next division. But be careful: You can be demoted awell!
If you are promoted to a new league, you have a small buffer so that you can't relegate straight away. If you lose too many games, you'll see a small yellow warning sign next to your rank. This tells you that your rank is at risk if you lose more games. If you continue to lose games, the sign changes to red. Then you are just before the demotion. After relegation, however, you don't start at 0LP, but at 75.
Each season is divided into three splits. In each split, you can collect split points by winning games. If you collect 250 split points in one split, your ranked armor will visually change. This way, you can upgrade your ranked armor up to three times per season:
You receive between 20 and 30 split points for each win, depending on whether you played your main role or won off-role (autofilled).
The promo helper is supposed to help you with promotion series of ranks that you already achieved before this season, but were then relegated. For example, if you were already Gold I, but then relegated to Gold II, you will receive a free win for your next Gold I promotion series. With that, you only have to win one more game to rank up.
The promo helper will also help you if you have just lost the promotion series to a new rank. As soon as you get back into the promo, you will also receive a free win.
Should you still lose the promo series (e.g. 1:2), it will be the same as before. The promo helper is only useful if you actually win the promo.
When moving up from one league ("tier") to the next, the promo helper is also activated. Since this is a best-of-5, you can collect not just one, but two free wins for your promo.
In general, the promo helper is only available up to Gold I. You then have to play the promotion series from Gold I to Platinum IV without it.
What is MMR?
Your match-making-rating (short: MMR) is a number that represents your rank. The MMR determines how many LP you win or lose per game. It is not visible to you, but it can be estimated based on your current rank and the LP that you get per game.
Ranked games are set up so that players with similar MMR are matched together in a game. For example, if you play DuoQ with a buddy, the average value of your both MMRs is taken to place you into the queue for a game.