How to split rent when you live with a couple?

[Dylan Albaugh]

Just curious what the general consensus is on this…say there's 2 friends that live in a 2 bedroom/2 bathroom apartment. The bedrooms and bathrooms are the same square footage so rent/utilities are split 50/50. Then one of the roommates has their partner move with them so they agree to split utilities 3 ways since they're all using them equally.

But how should rent be split between them (rent did not increase as a result of the partner moving in)? Should it still be 50/50 since nothing changed for the the single roommate, utilities are being split equally, and the couple is sharing one room? Or split evenly 3 ways since they are all living there? Or some other percentage like 40/30/30?

I wanted to see what others felt was fair. Please let me know your opinion. Thanks!