How do I get the Merge ending?

You have to save the geth I believe I did and it gave me the option

I didn't save the geth and I killed the elusive man and I got the merge ending I did how ever save the citadel and not the council in the first game

You had 5446 War Assets, or 5446 EFFECTIVE War Assets? I think you only get the Synthesis option at 5000 or better effective WA. I got it on my first playthrough, with the Readiness at 50%, so I don't think it's a matter of either of those, but I'm pretty sure my effective WA was somewhere in the mid-5000 range.

You will need to have at least 3000 Effective War assets and save Anderson(I had 3400 Effective War Assets and used all the blue paragon options in conversation with the Illusive man to make him shoot himself and I got the ending)

How do u know if you saved anderson? I shot him but TIM killed himself and he died sittin with shep

I have little over 3000 WA, Anderson died, and killed TIM but I still got it. I also killed the geth. I think it might have something to do with EDI and Jeff.

You need a total 2,800 EMS to get the third choice. Since you only had 2723 (5446x%50) you didn't unlock it. Try doing a few more side missions.

@cptnoblivious77 Thats not true i have over 3000ems and i didnt get the merge ending

I savedthe Geth and haved 96% readiness and only 4234 war assets i could still merge and in my opinion merging is the saddest thing to do combining Synthetics with Organics kill yourself and save the Reapers

I saved the Geth and had 92% readiness and 6204 war assets still it just gave me 2 options to become a reaper or to create synthetic-organic life.I dont think there is an ending with shepard living in the end if someone found a way please send us the way to do it too!!!!!!

Rating < 1750 - Earth is destroyed regardless of your choice
Rating 1751-2050 - If Shepard destroys the Reapers, Earth is destroyed.
Rating 2051-2350 - If Shepard becomes a Reaper, Earth is saved.
Rating 2351-2650 - If Shepard destroys the Reapers, Earth is only devastated.
Rating 2651-2800 - If Shepard destroys the Reapers, Earth is saved.
Rating 2801-4000 - Shepard can create a synergy between organics and synthetics.
Rating 4000-5000 - If Shepard destroys the Reapers and "saves" Anderson, Shepard
will also live as Earth is saved.
Rating 5000+ - If Shepard destroys the Reapers and does not "save" Anderson,
Shepard will also live as Earth is saved.

The score that you have at the end game is based on the green bar for your Effective Military Strength(EMS). You can raise the green bar by playing multiplayer or IOs games.

I was also told if you saved the human reaper in ME2 you needed a lower EMS for the merge ending. Im not sure if it is true or not

If you didn't destroy the collector base, you get an extra 300 EMS and TMS.

I think you have to get your galactic readiness up. I got 100% galactic readiness, and about 4500 war assets.

So play some multilayer

It's simple- get your readiness up, and go forward to the giant beam thing (do multiplayer, thats what I did, but I didn't do the merge or the indoctrination. I shot the power supply thang )

It depends on your paragorn/renegade status throughout all three games. I stayed fairly neutral and had all three choices, Control, Destroy, and Merge

Refuse to use the crucible at all and let the reapers have some fun then sit back and listen to liara's crappy tape.
Oh and to dimitris1982 not sure about the new endings bio ware have released but in the original endings that no one liked a full renagade play through off all three games then choosing to kill the reapers saw sheperd climb out the wreckage at the end of the game alive and well i did it my self.
So far on the new endings i've only done the synthesis one i had 91% galactic readiness 5441 effective military strengh and full renagade points even though i saved the geth and quarians i did it by telling the quarians i was going to watch the geth blow them out of the sky, i saved the rackni and qured the genophage with wrex in charge.

To get the merge/synthesis ending without doing multiplayer you have to do every side mission in the game otherwise you won't have the assets needed to unlock.