Matchmaking rating is an hidden data of your real League of Legends account rank. Your tier or division is only a representation at any time of your rank. It’s mainly affected buy your win / loss ratio and you can guess it, thanks to the amount of LP that you win or lose.
How does it work ?
MMR is directly impacted in many situations. First, if you are doing a losing strak at 0lp in Gold 4 for example, then your mmr will be closer from silver 1 than Gold4. However, there is visually no difference in your ranking (but you can notice a bigger LP loss). In the opposite case, imagine that you are at 99 lp in Gold 1 before accessing promotions to Platinum 4 and that you win 4 games in a row until Platinum. Your next wins are going to give you +20 lp on average, whereas you would win less if you were at 85 lp before your promotion followed by a 3-2 result in the best of 5.
We can estimate an average LP gain at 18 lp for each win. But we need to take into account each mmr of each player in every single game. Indeed, winning agaisnt better players with higher mmr than you are going to increase yours so that you are going to win more points. Account boosting is obviously a fast solution to fix his matchmaking rating. The advantage of account boosting is not only to increase the amount of points gained, but also to save more time.
Where can you check your mmr ?
Many websites exist to check his mmr You have access to this data on lol-mmr.com and see more details about your LoL account.
Credit: image from artstation.com