Does anyone actually know what determines LP gain/loss?

I hear it is your "MMR" match maker rating. Designed to help you climb faster if you deserve to be in a better tier.

If your friend gains more than he loses, his MMR must be high so the game is helping him get out of his tier. With higher MMR though, your friend also has to play against higher ranked opponents.

MMR increases by winning slowly over time.

What's the rationale behind downvoting questions? I've long stopped giving a damn about votes but it's still puzzling.

MMR

If you b5 with gold mmr you get more lip then a b5 with b5mmr

Your MMR, Teams MMR, Enemy MMR, game outcome.

when you win a game you gain LP

when you lose a game you lose LP

Although I'm sure MMR has the biggest determining factor in the LP gain, I have to assume that there's more to it than that. Here's what I THINK determines LP gain (in the 09/18 patch):

Forenote: Not making this a KDA section because deaths factor more into the MMR than kills or assists.

MMR: Factors between 30--55% of the LP gain/loss (if you've got a high MMR compared to your team, you'll lose less LP or gain more LP) Objective Score (Drag, Herald, Baron, Towers, Inhib, Nexus): Factors about 20% of LP gain/loss

Deaths: Deaths per match factor between 10-15% of LP gain/loss Kills: Kills per match factor between 5-10% of LP gain/loss. Assists: Assists per match factor about 5% of LP gain/loss CS: CS per match is determined by your role and lane (CS on ADC is more important than CS on Support, but generally has about a 5-10% factor on LP gain/loss

Vision Score: Vision score per match factors about 5% of LP gain/loss

This is by no means fact, I just find it hard to believe that MMR alone is the determining factor on LP gain/loss. Someone who does really well but loses because their team just sorta flopped shouldn't lose THAT much LP, although I guess if Riot wants to see who can carry low elo matches then it would make sense.