This article reveals the various different endings of Mass Effect 3.

(We were not sure if to include this warning - if you are reading an article about the ME3 endings, you can guess yourself that there will be spoilers. But we put the warning anyway, just in case...)

Factors affecting ending of the game:

Collector's Base: In Mass Effect 2, Shepard had to make a critical decision between the following options:
Destroying the Collector's Base
Leaving the Collector's Base to Cerberus

If you did NOT play Mass Effect 2, or if you started a new game on Mass Effect 3 WITHOUT importing a character, the assumed choice is:
Shepard Destroyed the Collectors Base

Note: You can achieve the perfect ending whether or not you destroyed the Collector's base. Main difference is that you get some additional war assets if you chose to save the collectors base.

Effective Military Strength (EMS): This is the War Assets, times the Readiness Rating.
On your War Assets screen you can see something like:
Total Military Strength: 6000
Readiness Rating: 80%
Effective Military Strength: 4800

That last figure is the determining number.

The lowest readiness rating you can have is 50%. Fastest way to increase the Readiness Rating is through Multiplayer. However, you should be able to achieve high enough EMS even without multiplayer.

Higher Effective Military Strength means access to a better ending.

Illusive Man Paragon/Renegade Ending: A 100% Paragon or Renegade rating unlocks a new blue/red conversation options when talking to the illusive man. After the illusive man says: "You... you'd undo everything I've accomplished. I won't let that happen." The dialog choices available are "But you already have", "Then you've failed humanity", "You're theirs now.", and  "You're Pathetic". If you unlocked the Paragon ending, the first two choices are Blue/Red PERSUADE options. Otherwise, those dialog options are grayed out.

Paragon Ending: Choose the blue option and you tell him that because of him, humanity is already undone. The Reapers have the Citadel. They've got all the species fighting each other instead of fighting them. You further tell The Illusive Man that he has done exactly what the Reapers wanted, and that he is still doing it because they control him. You try to tell Illusive man not to let the Reapers win and to break their hold.  Illusive man tells you he tried, and shoots himself in the head.

Renegade Ending: Choose the red option and tell him that he is weak and selfish, and because of him humanity will suffer. Illusive man insists he saved humanity, but you tell him that he sacrificed humanity for his own selfish wants and his lust for control. The Illusive Man persists in claiming he is the savior of humanity, the pinnacle of our species. He attempts to shoot you. Beat him to the punch.

Saving Anderson: Watch for the Renegade Interrupt to attempt and save Anderson. You will have to press the button quickly in order to shoot The Illusive Man before he shoots Anderson in the back of his head. HOWEVER, Anderson still dies, no matter whether you shoot Illusive Man fast enough or what. The difference is only whether or not he dies by being executed in the back of the head by TIM. If you manage to shoot Illusive Man before he shoots Anderson, there is also an extra scene where Anderson and Shepard sit together, you talk to Anderson and he tells you he is proud of you, before dieing.

Endings Spoilers:

First, we will give you a summary of all the endings based on your Effective Military Strength and on whether the Collectors Base was destroyed or not. Afterwards, scroll down to get a more detailed analysis of the events in the ending, and to understand what goes on in the cutscenes.

Collector's Base Destroyed

0 to 1,749 EMS:
Your only choice is to destroy the Reapers. Earth is destroyed.

1,750 to 1,899 EMS: Shepard can choose to destroy the Reapers, or control them. If you destroy the Reapers, Earth is destroyed in the process as well. If you control the Reapers, Earth is devastated but not destroyed.

1,900 to 2,349 EMS: Shepard can choose between destroying and controlling Reapers. Both choices save earth, and humanity survives, however Earth's buildings still get vaporized.

2,350 to 2,649 EMS: Shepard can control Reapers, and save Earth

2,650 to 2,799 EMS: Shepard can destroy Reapers, and save Earth. Shepard Dies.

2,800  to 3,999 EMS: Shepard is able to create a link between Synthetics and Organics,  and Earth and the Galaxy are saved

4,000 to 4,999 EMS: You can destroy the Reapers and Earth is saved. If you shot TIM on time and saved Anderson, Shepard breathes (Survives).

5,000+ EMS: You can destroy all Reapers. Earth saved as well. Shepard will breath, whether you attempted to save Anderson or not. (Perfect Ending)

Collector's Base Remained Intact

0 to 1,749 EMS: 
Shepard's only choice is to destroy the Reapers. Earth is destroyed.

1,750  to 2,049 EMS: Shepard can control the Reapers or destroy them. Destroying the Reapers also destroys Earth. Controlling the Reapers damages earth but does not destroy it.

2050 to 2,349 EMS: Shepard has choice between controlling and destroying Reapers. You save Earth from destruction either way, and humans live, but Earth is still devastated and buildings vaporized.

2,350  to 2,649 EMS:  Shepard can destroy the Reapers. Earth is badly damaged but isn't destroyed completely

2,650 to 2,799 EMS: Shepard can destroy the Reapers and save Earth.

2,800 to 3,999 EMS: Shepard can create the Synergy between Organics and Reapers to save Earth and the Galaxy

4,000 to 4,999 EMS: Shepard can destroy Reapers.  Earth survives. If you shot The Illusive Man on time and saved Anderson, Shepard Survived.

5,000 + EMS: Shepard can destroy Reapers. Earth survives. Shepard also survives regardless if you tried to save Anderson or not. (Perfect Ending)

Ending Explanation:
The Catalyst tells you that you have choice, more than you deserve, as you are the first Organic ever to stand there. The choices presented to you depend on your War Assets (Effective Military Strength)  The Crucible created new possibilities. You can DESTROY it and wipe out synthetic life including the Geth. But the Reapers will be destroyed. Releasing the energy of the Crucible will end the cycle. But it will also destroy the Mass Relays. Or, you can CONTROL the Reapers. You will die. You will control them, but lose everything you have. The Reapers will obey you. The third solution is SYNTHESIS. You can add your energy to the Crucible's. Everything you are will be absorbed, and then sent out. The chain reaction will combine all synthetic and organic life into a new framework, a new DNA. The cycle will end. Synthesis is the final evolution of life.

The paths are open, but you have to choose/There is only one way ahead. (You may or may not have a choice here, depending on your readiness rating)

Destruction: Shepard advances towards the Catalyst beam, turning right. He raises his weapon and shoots the relays, initiating the destruction scene.

Controlling the Reapers: Shepard advances towards the catalyst beam, then turn left, drops his gun, and places both arms on the energy receptacles, as he turns into a Reaper and gives them the command to cease fire.

Synthesis: Shepard drops his weapon and heads toward the center, then jumps into the Catalyst Beam.

Cutscene Explanation:

Energy waves from the crucible have a different color depending on what Shepard chose.
Destroy Ending: RED ending. Three possible endings under this scenario are: Destroy Vaporization/Destroy Bad/Destroy Good
Control Ending: BLUE ending. Two possible endings are Control Good/ Control Bad
Synergy Ending: GREEN ending.  Only possible ending is Synergy Good

Earth's Fate:
If Shepard chose to destroy the Reapers, a big wave of flames sweeps through the Earth. With a low EMS score, the movie will show the flame wave destroying everything in it's path, including Reapers, buildings, and humans. Earth is destroyed.

Medium score on the Effective Strength causes the humans to live, however Earth is heavily damaged by the blasts, and buildings get vaporized.

With the higher Effective Military Strength Score, the energy wave destroys the Reapers but leaves buildings intact, and does not kill the humans. Earth is not destroyed.

If Shepard chose to control the Reapers, the cutscene will show some electric activity on the Reapers, and the Reapers will leave Earth. With low EMS, many buildings are destroyed in the process. With high EMS, buildings remain intact.

If Shepard chose the Synergy path, the Reapers depart from Earth and Earth is saved.

In cases where humans survived, the soldiers on the ground cheer as the Reapers either leave Earth or are destroyed.

Normandy Crew Fate:
The cutscene shows Joker at the bridge of the Normandy SR-2, attempting to outrun the big energy wave that is chasing the Normandy. The wave catches up after a while, sucking the Normandy in. The Normandy crash lands on a deserted planet, but the squadmates survive.

Shepard Survives:

When you reach an ending in which Shepard lives, in the end of the cutscene you will be taken to the ruins of the citadel and see Shepard's body (identified by his Dog Tag). Suddenly you will see and hear Shepard breathing.

After Credit Epilogue:
An old man, and a child, are walking on a planet looking at a big moon.
Stargazer:  Our galaxy has billions of stars. Each of those stars could have many worlds. Every world could be a home to a different form of life. And every life is a special story of its own.
Child: Tell me another story about the Shepard
Stargazer: It's getting late, but, okay... one more story.

This leads to open world mode:

Free Roam
Commander Shepard has become a legend by ending the Reaper threat. Now you can continue to build that legend through further gameplay and downloadable content (DLC),
This puts you in free roaming mode, and resets the game to just before Shepard's attack on the Illusive's man base. Reapers will be located at different systems across the galaxy map, so feel free to go and explore. You will also be able to install future DLCs that will add content to the game.