How to use the home office percentage calculator
- Enter the total area of your home in any unit, such as square feet or square meters.
- List each space you use for work with its area and the share of the time it is used for work.
- Optionally add yearly home costs, such as rent, utilities and insurance, to split.
- Read the business share of the home and the part of each cost it covers.
Formula
share of the home = area of the space / total area of the home
counted share = share of the home x business use of the time
business use of the home = sum of the counted shares
business share of a cost = yearly cost x business use of the home
Each cost line is rounded to the cent, and the total adds the rounded lines so the table always adds up.
One room in an 1,800 square foot home
A home office of 180 square feet in a home of 1,800 square feet is 10% of the home. Used only for work, its counted share is 10%. Yearly rent or mortgage interest of $18,000, utilities of $2,400 and insurance of $1,200 add to $21,600, and 10% of that is $2,160, leaving $19,440 as personal.
A spare room of 150 square feet used 40% of the time for work counts for 150 / 1,800 x 40% = 3.33% of the home. An office of 120 square feet used fully plus a garage corner of 80 square feet used half the time counts for (120 + 40) / 1,800 = 8.89%.
Area share and time share
Many people measure only the room they use. Adding the time share lets you include a space that is used for both work and family, by counting only the part of the time that is work. Keep the measurements and a record of how you arrived at the time share, since a rule or a reviewer may ask you to show them.
The result is arithmetic and not an answer about what you can claim. Keep your yearly costs in the Expense Tracker or plan them in the Budget Planner. Utility bills can be compared with the Energy Tariff Comparison Calculator.
What this tool does not decide
Whether any part of your home costs counts as a business expense, which costs qualify, how a space must be used and what records are needed depend on the tax rules where you live. They change over time and differ by type of work. Talk to a tax professional before you rely on a figure from this page.
Assumptions and limits
- All areas use the same unit, and the work spaces together are not larger than the home.
- Costs are spread in proportion to area, which is one way to share them and not the only one.
- The time share is your own estimate and should reflect real use.
- No tax rules, caps or rates are applied, and nothing here is tax advice.
Frequently asked questions
Should I count the hallway and the bathrooms in the total?
Use the total area that you and your records agree is the home. The more consistent your measurement is from year to year, the easier it is to explain.
What if I use the room only on weekdays?
Enter the share of time the room serves work. A room used for work on weekdays and left idle otherwise might be near 70% of the time, depending on how you count idle time.
Can I split a cost that is not by area, such as internet?
You can enter any yearly cost and the tool applies the same share. If you use a different share for that cost, such as the share of hours online, calculate it separately.
Does the tool store my numbers?
No. The calculation runs in your browser, the names you type stay out of share links, and nothing is uploaded.