What is the range for co-op in Bloodborne?

I'm a bit hesitant to level up too much because I like playing co-op, so I'd like to know how the range to summon and to be summoned is calculated.

Does it work by level, like in Demon's Souls and Dark Souls? What are the ranges and can you have any influence on them?

The summoning range has since been updated via patches. As of patch 1.05, research found here indicates the following rules:

Let x be your level.

For upper limit of level you can summon:

x + 20% + 20

For lower limit of level you can summon:

x - 20% - 20

For upper limit of level you can be invaded by:

x + 10% + 10

For lower limit of level you can be invaded by:

x - 20% - 20

It should also be noted that if you are using passwords to summon a friend, this limit will be ignored and you can summon them regardless of their level. Players who are significantly higher than the summoner who are summoned this way will have their levels scaled down.

Here is a nifty calculator which does the math for you!

http://www.reddit.com/r/bloodborne/comments/30d6wo/psa_how_to_calculate_your_coop_range/

TLDR:

your level * 0.1 = x

maximum level of coop: your level + x + 10

minimum level of coop: your level + x -10

Basic algebra needed, (very basic) but I hope this helps.

EDIT: It's the same as DkS and DeS summoning, so google a Dark Souls 1/ Demon Souls summoning calculator, it's far easier and requires you to use less brainpower.

EDIT #2: Make sure you and your friend(s) are using the same network password, which can be found in settings, network.