The max for everyone is currently 3%, and it's also broken so it gets stuck at 3% once you hit it
This is actually no longer true. Everyone was reset to 1%.
Bank Interest has been reset to a yearly rate of 1%. Users can increase this rate by 1% for 24 hours by collecting interest. Activating a Morty Card will increase the interest rate by 1%.
As mentioned above, however, it is a bit bugged so the rate might stick at 3% instead of going back down to 1%.
Yeah, explained it pretty well. The 1% interest is already added into the 3%, but once you get it, it tends to stick rather than dropping after 24 hours like it's meant to.
Morty Cards are actually broken in that the timer that's supposed to count down their expiration, actually counts up as time goes on, so you'll have that extra 1% forever until they get fixed.
The cap is 3% though, regardless of bonuses or anything. It might get raised later with new ways to earn extra interest, but nothing has been announced yet.