This guide is primarily based on datamining from gamefiles and personal experiences of players with MMR without any official statements from BHVR and so, it's not your most definite and reliable source of the most accurate infos about SBMM and MMR in DbD.
Any suggestions on improvement are more than welcome.

This guide is meant to answer most of your questions about skill-based matchmaking and matchmaking rating.

If you need some quick answers to your questions, be sure to refer to PART 4: MMR FAQ.

Matchmaking rating, also known as MMR, is a core element of skill-based matchmaking, also known as MMR.
MMR is a hidden stat that is basically a numerological representation of player skill, earned or lost by specific match outcomes.
It was created in order to make matches more fair and thus more enjoyable.
DbD matchmaking has three most important DbD milestones:
650 - initial MMR
1600- soft MMR cap
2100 - hard MMR cap

When you start playing one role for the first time, you are being placed into a calibration queue for that role.
This means that you are about to play couple of matches so that game can determine your skill level and so give you the proper MMR score (you are not gaining nor losing MMR points during calibration queues).
Note: Calibration queues exist to prevent smurfs from just simply creating new accounts so they can instantly play with newbies, make another new account so they can do the same, and so on.

After calibration, you are oficially put into a MMR bracket corresponding to your skill level.

In order to explain how MMR points are gained and deducted, we will have to take a look into:

• base MMR gain/loss criteria
  
• modifiers for survivors
  
• modifiers for killers

The most basic factors that determine if your MMR points output are:
SURVIVOR

KILLER

There is one modifier that exclusively affects your survivor MMR outcome, and that is:

• SWF modifier

How does this modifier work? Well it's simple, it influences the final MMR outcome depending on what happened to you + what happened to other survivors you have queued with.
Here is a table for better understanding:


This modifier does not exist when you are playing soloQ, technically meaning that it's easier to have bigger MMR gains, but also MMR losses there too. However, it comes into play as soon as at least one person queues up together with you.

NOTE: The exact value of SWF multiplier of MMR is still secret and will probably never be clear due to MMR score always being hidden and more factors affecting MMR outcome, due to which it's impossible for community to get to know this.

Killers don't have any additional modifiers that affect their MMR outcome but, in difference to survivors, every killer has their own MMR score. This is the true reason why you can't switch killer once match has been found (and additionally prevention of abusing the matchmaking system by picking lowest MMR killer to get an easier lobby, and switching to your highest MMR killer in the pre-match lobby.

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However, there is something called killer MMR rubberbanding. MMR rubberbanding basically works like this:
The killer you play the most has the highest MMR score out of all other killers, and initial MMR score of other killers is dictated by it.
When you reach the soft MMR cap (1600 points) with at least one killer, the MMR score of every other killer you own that was below 1200 points will automatically be raised to 1200 points (just so you can't be at the MMR floor (1000 points) because game automatically assumes you have enough "macro" knowledge to play the killer to bare minimum of mechanical knowledge, but still make the game fair for survivors.
In other case, where your most played killer still hasn't reached soft MMR cap, your other killers will be put at MMR floor.

NOTE: Any new killer you buy after reaching soft MMR cap with at least one killer will also be automatically raised up to 1200+ MMR points.

There are two kind of general MMR modifiers:

• Match length modifier;
  
• Modifier based on opponent(s) MMR.

We'll break these two down in the upcoming part.

Match length modifier affects your final MMR outcome in match depending on how much the match lasts and is maxed at 10mins.
Here is a small chart of multiplier throughout the match:

The multiplier rises steadily until you reach 10th minute. From that point, it stays at the max value until the end of th match, when finall MMR outcome is calculated. The same goes for winning and losing and match, the more it lasts, the greater win/loss multiplier is.

NOTE: This multiplier applies both to survivors and killer.

This modifier is very simple and it determines your outcome by opponent's MMR and the very fact if it's higher or lower than yours.

Now we are about to talk about the most notorious aspect of MMR system in DbD: matchmaking ladders, or in other words, the way how you are being matched with players and how your matchups are being decided.

To explain matchmaking in general, we will first take a look at these two charts:

*MMR range of opponents based on your MMR*
NOTE: The range of opponents poll extends based on the current amount of players who queued for the role you are playing against. For example, if there is 100% survivor BP incentive due to lack of survivor players in your region and you queue up as killer, game will extend the poll of players to match you with, making your matches less accurate skill wise, but accellerating the process of match finding.

*Approximate share of players per MMR points range*

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As you can see from the 2nd chart, calibration ladder has the least players, while most players are allocated in 1600-2100 MMR ladder. This fact is very problematic for DbD matchmaking and is the result of soft MMR cap being too easy to hit.
Most MMR points you can get in a DbD trial is 20. Let's assume you are gaining half of it, 10, every match and that you have been placed at 900 MMR score after initial calibration.
You technically need only 70 winning matches in order to reach soft MMR cap. Let's assume average match of yours lasts 15 minutes. This means that, in a perfect scenario, you would reach soft MMR cap in just 17.5 hours. Take in mind the time required to learn fundamentals of the game before reaching soft MMR cap and you would be left at only ~100h needed from beginning with DbD to reaching soft MMR cap.
So, why is soft cap being so easy to achieve actually problematic? Well it is problematic because of couple things:

• you only know fundamentals as a player that has ~100h into the DbD and you are basically about to be put into matches against people with way more skill than you.
  
  
• playing as an experienced DbD player would mean basically winning against 90%+ of lobbies because chances of actually getting matched against someone that is truly similar skill level to yours in a sample this big (check both charts) are extremely small, game just treats anybody from 1600 to 2100 MMR score as the same skill level.

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However, the reason behind BHVR putting soft MMR cap this low might just be nothing more than it serving as a bandaid for the very problematic nature of game balance.
In the top skill levels, game is incredibly difficult to balance due to survivor role being so powerful at the highest skill levels and just plain better than almost every killer.
With this in mind, most of DbD players are not really that good, and that would be the reason why BHVR made MMR so loose.
With the MMR in this state, the balance is pretty much achievable due to the fact that you would verse players of extremely varying skill levels, further meaning that you will stand a great chance against survivors as the killer because you are playing against varying survivors rather than playing against someone of your own skill level.

A: DbD is a PvP game with set win conditions and learning curve for both sides, meaning huge part of playerbase plays to win. MMR exists in DbD as an attempt to secure fair matches where all players could be as close with skill level as possible.

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A: MMR is hidden with a clear purpose: to prevent it's abuse. If MMR was visible, people could use that info to actually forcefully drop their MMR score in order to get easier opponents. It's not just DbD, every game with SBMM system has the MMR score hidden from it's players.
And one note: Rank in DbD does NOT equal your MMR at all.

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A: The answer to this depends on lot of things. Tho the things that impacts this the most is the fact that game basically considers everyone between 1600 - 2100 MMR points (soft MMR cap - hard MMR cap) as having equal level of skill and so considers everyone in that range as eligible to be matched with each other. Due to this, you can have teammates that just decide to throw the match for challenges and/or various personal reasons, or have just reached soft MMR cap without actually trying to learn much (hardstuck 1600 MMR players).
Being in a duo with another person as 2-people SWF also has a great impact on this.

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A: You are not getting top MMR survivors, in most cases you will be matched against average survivors at best, because matchmaking bracket is overly populated with average players around soft MMR cap. This is the part where your macro gameplay learning curve begins.
You are having big troubles if you play M1 killers, but with the other ones you should be able to have at least 50% winrate once your macro gameplay knowledge develops well.

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A: As already mentioned in this guide, soft MMR cap is so easy to reach that you can literally be a ~100h player knowing only fundamentals and be matched with way better players than you. This means you will sometimes be placed into lobbies against those people who lack deeper game knowledge in other to stand greater chance against you.