Which split is fair?
Equally is simplest when incomes and rooms are similar. By income means everyone gives up the same share of their pay, which many couples find fairer when one earns much more. By room size suits roommates with very different rooms; it is common to split rent by room and share bills like internet equally. Agreed % covers anything else you settle on.
The fairness check shows each person's shared costs as a share of their take-home pay, so you can see the effect of each choice before you agree. There's more on setting up shared money in our guide to budget apps for couples.
Privacy
Everything is worked out in your browser. A copied link holds the names and numbers you typed, so share it only with the people involved.