Split By Space
If you have a big apartment or house and space is rented unevenly, asking the person using lesser space for 50% isn't really justified. So, if you are using two rooms while your roommate is using one, it's ethical to pay 66% and ask your roommate for 33%.
Split by Income
If you're living with a really close friend or with a spouse and still want to split the rent, it's a great idea to split by income. It helps both of us get through things together without putting too much financial pressure on one individual.
Split Evenly
The most basic way to split the bill is by splitting it evenly. If there are two people living in an apartment, they'll both have to pay 50% regardless of the amount of space they're using. If you're living conditions are completely split into two, splitting the rent 50-50 is the best idea.
