How an Income Change Shifts Roommate Rent Shares
In this self-created rent test, changing only Cam’s entered income from $2,500 to $3,500 changes the income-based shares from Ava $1,108.86, Ben $703.70, and Cam $533.11 to Ava $1,016.46, Ben $645.06, and Cam $684.15. The total stays $2,345.67 in both runs. These are synthetic inputs, not observed renter data or a recommendation about what anyone should pay.
The two runs
The rent, names, room IDs, and private-area entries stayed fixed. Only Cam’s income entry changed. This comparison uses the rent calculator’s income method; it does not compare room-based or area-based allocation.
| Person | Income before | Share before | Income after | Share after | Change |
|---|---|---|---|---|---|
| Ava | $5,200 | $1,108.86 | $5,200 | $1,016.46 | −$92.40 |
| Ben | $3,300 | $703.70 | $3,300 | $645.06 | −$58.64 |
| Cam | $2,500 | $533.11 | $3,500 | $684.15 | +$151.04 |
| Total | $11,000 | $2,345.67 | $12,000 | $2,345.67 | $0.00 |
The changed run reduces Ava’s modeled amount by $92.40 and Ben’s by $58.64, while Cam’s rises by $151.04. The changes balance: $92.40 + $58.64 = $151.04. The rent total is unchanged.
How the income share is calculated
For this tool, one person’s unrounded share is the entered rent multiplied by that person’s entered income, divided by all entered incomes. The calculator then allocates whole cents so the displayed shares reconcile to the rent.
In the first run, total entered income is $5,200 + $3,300 + $2,500 = $11,000. In the second, it is $5,200 + $3,300 + $3,500 = $12,000. The rent remains $2,345.67. The relative income weights change, so each income-based share is recalculated; no rent is added or removed by the change.
This demonstrates the behavior of the site calculator for these inputs. It does not establish that an income-based split is fair, required by a lease, or appropriate for a particular household. The entries must represent comparable periods and the same gross-or-take-home basis for the tool’s ratio to be interpretable. For converting different pay periods, see the income-period calculator guide.
Reproduce the test
Enter rent of $2,345.67 and the three incomes in the table into the rent split calculator, choose “By income,” and record the results. Change only Cam’s income to $3,500 and calculate again. The two input/output sets are available as JSON; the compact replay model applies the same income weights and cent-allocation rule. The replay model SHA-256 is 56a49a575d8a7c82c234239ac5875707de180a0565c40f0237a70011397a6754. The production calculator script used for the recorded test is linked at the deployed calculator code; its SHA-256 is 45a10a5b41e6388847352e910e9f08174f294b5cbe7f929bb724a9f9aa154992.
The calculation was run in a local Node virtual machine with a minimal form-field shim against the site calculator JavaScript. It was not a visual browser test, payroll verification, real household record, typical-rent study, fairness finding, or lease interpretation. The input values were made for this example.
What this result does and does not say
The exact outputs and changes above are reproducible for the saved inputs and code. They show one controlled change in the site’s income-weighted calculation. They do not show how often incomes change, how roommates actually negotiate rent, or that similar examples do not exist elsewhere. Use the method only if the household has agreed to it and check applicable written rental terms separately.