RUBS calculator: split one utility bill across your units

A RUBS calculator takes one shared utility bill and divides it across the units that use it, by a ratio you choose: occupants, square feet or an equal share. The share is the unit's weight divided by the total weight, times the bill, rounded so the cents add up to the bill exactly. The calculator above does that on your own rent roll (CSV or Excel) with no sign-up, and the rest of this page shows the arithmetic so you can check any answer by hand.

How do you calculate a RUBS share?

Each unit's share is its weight divided by the sum of every sharing unit's weight, times the bill. The weight is whatever ratio the property uses. Take a $600.00 gas bill for four units with 700, 900, 1,100 and 1,300 square feet. The total is 4,000, so each square foot carries $0.15, and the units pay $105.00, $135.00, $165.00 and $195.00. Those add up to $600.00.

The same four units split by occupants would give a different answer. If they house 1, 2, 3 and 4 people, the total weight is 10 and each person carries $60.00, so the shares are $60.00, $120.00, $180.00 and $240.00. A unit's share moves a lot with the method, which is why the method is a property setting you choose once, not a per-bill decision.

Which method should the calculator use: occupants, square feet or equal?

Use the method your lease or your rules say, because the lease is what the tenant agreed to. The calculator supports three:

• Occupants. Weight is the number of people on the lease. It follows use for water and sewer, and it needs an occupant count you keep current.
• Square feet. Weight is the unit's area. It needs no occupant data, and it is common for gas and heating shared across a building.
• Equal share. Every unit weighs 1. It is the simplest, and the usual choice for a flat trash charge.

Which one is allowed, and how it must be disclosed, varies by state, city and lease. This page is not legal advice: check local law and your leases before billing tenants.

What happens to the extra cent?

Dividing money rarely comes out even, so a split needs a rounding rule that keeps the total exact. Split $100.00 equally across three units and each share is $33.333... Rounding each down gives $99.99 and loses a cent; rounding each normally gives $99.99 or $100.01 depending on the amounts.

The method that always works is largest remainder: work in whole cents, give every unit the whole cents of its share, then hand the leftover cents one at a time to the units whose shares had the biggest fractions. Here the shares become $33.34, $33.33 and $33.33. Utility Billback uses this in whole cents, so the charges always sum to the bill.

How do move-ins and move-outs change the split?

A tenant who is in the unit for part of the service period should pay for part of it. The calculator weights each lease by its basis (occupants, square feet or 1) times its days in the service period, with the first and last day both counted. A tenant who moved in on the 12th of a 30-day period carries 19 of the 30 days.

Say a bill covers 30 days for three equal-weight units. Unit 3's tenant moved out after day 20, and the unit sat empty after that. The weights are 30, 30 and 20, with 10 vacant unit-days left over: 90 in all. On a $300.00 bill each weight is worth $3.3333, so units 1 and 2 pay $100.00, unit 3's tenant pays $66.67 and the last $33.33 is the vacant days. The RUBS billing guide walks through proration and vacant days in more detail.

Who pays for vacant days?

Whoever your rule says, and the calculator offers both. With vacant days kept by the owner, an empty unit's share stays with the owner, so the tenants never subsidize it. With vacant days shared, only occupied unit-days split the bill, so the tenants cover the empty unit. Pick the one your leases support. Keeping vacant days with the owner is the safer default when the lease is silent, and it is the calculator's default.

What does the calculator need from you?

• A rent roll as CSV or Excel, up to 4 MB, with a row per unit or lease: address, unit, tenant, lease start and end, occupants and square feet.
• The bill: the utility, the amount and the service period's first and last day.
• The method and the vacant-day rule.

Your file is read in memory and not kept. The result lists each unit's share and the owner's share, and you can download the charges as a CSV. If a column such as the utility's payer is missing, the calculator treats every unit as sharing the bill, which is what a visitor asking for a split usually means.

What does a RUBS calculator not do?

It splits one bill, once. It does not read the bill PDF for you, decide whether the bill belongs to a tenant account, know your state's limits on RUBS charges, or post anything to AppFolio or Buildium. For the monthly job across many bills, see utility billback for property managers, which covers matching each bill to a unit and lease and the bills still in your company's name. If you are comparing ways to run the whole job, RUBS utility billing lays out the options.

Check the result yourself

Before you trust any split, multiply a unit's weight by the per-weight rate and compare it with the calculator's figure, then add the shares and the owner's share to confirm they equal the bill. If they differ by a cent, check the rounding. If they differ by more, the rent roll's occupant or square-foot columns are the usual cause. You can also see a whole month on a sample building, with four bills and a charge list, before you use your own data.

Frequently asked questions

Is a RUBS calculator the same as ratio utility billing?

Yes. RUBS stands for ratio utility billing system, and the calculator applies that ratio to one bill. The ratio utility billing system guide explains where each ratio fits.

Can I split a bill by square feet and occupants together?

Not in one split. The calculator uses one method per bill. If your lease combines factors, work out the combined weight in a column of your rent roll and use it as the square feet or occupants figure, then check the result against the lease.

Does the calculator keep my rent roll?

No. The file is read in memory to produce the result and is not kept. Reading bill PDFs and storing a month's data happen only in the paid app, with a 13-month retention.