Enrichment · Life Skills

Split the rent. Settle the rest.

Divide the rent evenly, by room size, by income or by your own percents. Log the bills and groceries as they come. The calculator works out each share to the cent and a short list of payments that leaves everyone even.

Split this month What you get

The calculator

The worked example is three roommates, $2,400 a month and seven shared costs. Change any number and the shares and payments follow. Nothing you type leaves this browser.

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What you get

Enrichment · Life SkillsFree

What you finish with: Each roommate’s rent under the rule your household picks, a side-by-side look at the other rules, every bill and purchase split to the cent, each person’s total for the month, and a short list of who pays whom to settle up. Copy it into the group chat, print it or save a spreadsheet.
Who it is for: Students and young adults moving into a first shared apartment, roommates who want one clear monthly reckoning, couples and families sharing a home, and life skills and personal finance teachers.
Format: Browser tool. Works on a phone or computer. Copy as text, print or save as PDF, a .csv spreadsheet, and a file to move the household between devices.
Access: Free. No account and no sign-in. Names and amounts stay in this browser; nothing is sent to Caveat.
Where it lives: The Life Skills space in Caveat Enrichment.
Support: Questions, a correction or a request: team@caveatacademic.com.

Settling up nets everything first. Dozens of receipts become one balance per person, then a few payments that bring every balance to zero.

How to use it

Add everyone who lives in the home and choose the month.
Enter the rent, who sends it to the landlord, and how you want to split it. For the room-size split, measure each bedroom and, if you can, the whole home.
Log each bill and shared purchase: what it was, the amount, who paid and who it was for. Tap a name to leave someone out of a cost.
Read the payments at the top of the results. Open the comparison to see what the other splitting rules would charge.
Copy the summary into the group chat, or print the month and keep it with the lease.

Split this month

How the split is worked out

Rules a household can check by hand, in whole cents, so every split adds back to its total.

The rules

Add-ons first. A set amount for a private bathroom or a parking spot comes off the rent, and that person pays it on top of their share of the rest.
Evenly: the rest is divided by the number of people. By income: in proportion to take-home pay. Your own percents: exactly as typed, and they must total 100.
By room size: the part of the rent that pays for shared space (kitchen, living room, hallway) is split evenly; the part that pays for bedrooms is split in proportion to each room’s square feet. If you enter the size of the whole home, the shared part is everything that is not a bedroom.
Cents: each share is rounded down to the cent and the leftover cents go to the largest remainders. When shares tie, the extra cent rotates from entry to entry so no one always pays it.
Settling up: the page nets what each person paid against what they owe, then pairs the person who owes the most with the person owed the most until every balance is zero. That takes at most one payment fewer than the number of roommates.

Good to know

No formula is the fair one. A bigger room, a window, a closet or a longer walk to the bathroom is worth different amounts to different people. Agree on the rule before anyone signs.
When roommates sign one lease together, each of them can usually be held responsible for the whole rent if another does not pay. How you split it among yourselves is a private agreement, so put it in writing.
The room-size rule treats every square foot of bedroom the same. If one room is plainly better, use an add-on or your own percents.
Security deposits, a roommate moving out mid-lease and utilities in one person’s name are not modeled. Note who holds each account and how a move-out is handled.

The worked example, checked when the page is built. Three made-up roommates pay $2,400. Ari pays a $60 add-on for the private bath, leaving $2,340 to split. The bedrooms are 150, 120 and 110 square feet in a 950 square foot home, so 60% of it is shared: $1,404 is split evenly ($468.00 each) and $936 goes by room size ($369.47, $295.58 and $270.95). Rent comes to $897.47, $763.58 and $738.95, which adds back to $2,400.00. Seven bills and purchases total $371.05. Ari sent the rent and paid three of them, so Cole pays Ari $786.24 and Bea pays Ari $755.36, and everyone is even.

Sources

Francis Edward Su, "Rental Harmony: Sperner’s Lemma in Fair Division," The American Mathematical Monthly 106, no. 10 (1999): 930–942: the mathematics of pricing rooms so that each roommate prefers their own. This page uses simpler rules a household can check by hand.
U.S. Census Bureau, "Methods of Apportionment" (census.gov): the Hamilton method of largest remainders, used here to hand out leftover cents so each split adds back to its total.
Legal Information Institute, Cornell Law School, Wex legal dictionary, "joint and several liability" (law.cornell.edu/wex): why co-tenants on one lease can each be asked for the full amount.

General information, not legal or financial advice. Lease terms and tenant law differ from place to place; your lease decides what each tenant owes the landlord. The worked example and its names are made up. Support: team@caveatacademic.com.