Methodology
How RentSplit Calculates Rent
RentSplit keeps the chosen allocation method, optional assumptions, and whole-cent reconciliation visible so roommates can review the same calculation.
Five full-rent allocation methods
Equal by room
The private rent pool is divided equally among rooms. With no shared-space percentage, each room receives the same share of the complete rent.
Room size
The private rent pool follows each bedroom's share of total positive bedroom area. Area can be entered in square feet or square meters; the calculator normalizes the units before allocation.
Equal by person
The complete rent is divided equally across all occupants, then grouped into room totals. A room with two occupants receives two per-person shares.
Custom percentage
Each room receives its entered final percentage of the complete rent. Percentages must be non-negative, use at most two decimal places, and total exactly 100%.
Custom monthly amount
Each room receives the entered final monthly amount. Every amount must use whole cents, and the room amounts must total the stated monthly rent exactly.
Equal by person, custom percentage, and custom monthly amount are final full-rent methods. Shared-space and room-adjustment layers are disabled for those methods to avoid applying the same assumption twice.
Shared-space allocation
For equal-by-room and room-size calculations, a user may identify a percentage of rent as the common-space pool. That pool is allocated by the number of occupants in each room. The remaining private pool follows the selected room basis.
Worked example
A $3,000 home has two bedrooms. Room A has two people and 120 square feet; Room B has one person and 80 square feet. With 30% assigned to common space, $900 is split by three people, so Room A receives $600 and Room B receives $300 of common-space rent. The remaining $2,100 follows the 60/40 bedroom-area ratio, producing $1,260 and $840. Final room totals are $1,860 and $1,140.
Room adjustments and private bathrooms
Visible premiums and discounts modify an equal-by-room or room-size baseline. When one room receives an adjustment, the same amount is offset across the other rooms in proportion to their non-negative base rents. If those base rents provide no usable weight, the offset is divided equally among the other rooms.
Private bathroom value is represented by an explicit fixed premium for a selected full or half bath. A bathroom label alone changes nothing. The user chooses the assumption, and the result lists it separately from the base allocation.
Adjustments must remain finite, whole-cent representable, and cannot produce a negative room rent. They do not change the stated total rent.
Rounding and integer-cent reconciliation
Accepted money is converted to integer cents before final allocation. RentSplit first calculates each proportional quota, assigns the whole-cent floors, then distributes any remaining cents by the largest fractional remainders. Ties follow stable input order.
This deterministic process keeps every displayed allocation at whole-cent precision and makes the displayed room totals reconcile exactly to the stated rent. It avoids independently rounding each share and accidentally creating a missing or extra cent.
Examples of the final-share methods
- $3,000 across two rooms equally becomes $1,500 and $1,500.
- $3,000 across three people equally becomes $1,000 per person, grouped by room occupancy.
- A 55% and 45% custom split becomes $1,650 and $1,350.
- Custom monthly amounts of $1,725 and $1,275 are accepted because they total $3,000 exactly.
Privacy and review boundaries
RentSplit is a static browser tool with no account, runtime API, database, cookie, autosave history, or third-party tracking collector. The normal calculation remains in the current browser session unless the user explicitly creates a review link or saves the one supported device-local snapshot.
Shared review links contain a versioned calculator draft in the URL fragment. The fragment is handled in the browser and is not sent as part of a normal HTTP request. The income-based calculator follows a stricter boundary: income values are not placed in links, local storage, metadata, events, logs, or requests.
Limitations and discussion-aid boundary
The calculator models only the inputs and formula selected. It does not inspect a lease, determine legal obligations, price a local housing market, evaluate affordability, establish a universal definition of fairness, or replace a roommate agreement.
Utilities, deposits, damages, taxes, payment schedules, and changing household circumstances may need separate rules. Use the output as a transparent starting point for discussion and record any final agreement separately.
Methodology FAQ
Why can a displayed share differ by one cent from a raw decimal?
RentSplit converts the total to integer cents, calculates proportional quotas, and assigns any remaining cents deterministically so the displayed shares add back to the exact stated total.
Does RentSplit decide which method is fair?
No. The calculator applies the method and assumptions entered. Roommates still need to decide which assumptions fit their household and any existing agreement.
Are shared spaces included in every method?
Shared-space allocation is available for equal-by-room and room-size methods. Equal-by-person, custom percentage, and custom monthly amount are final full-rent methods, so they do not add a separate shared-space layer.
How are private bathrooms handled?
A private full or half bathroom changes rent only when a visible fixed premium is entered. RentSplit does not infer a universal bathroom value.
Does RentSplit save the calculation automatically?
No. The main calculator can create one explicit device-local snapshot when the user chooses Save on this device, and shared review links use a versioned URL fragment. The specialized income tool does not save or share income inputs.
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