1. Rent and space
Start with rent received and a documented allocation method.
Square footage is the default method. Measure the rented room and the finished home the same way you would document them for your records.
2. Optional room-count method
IRS Publication 527 also mentions number of rooms as a common method. Fill both fields to compare.
3. Annual whole-home costs
Enter yearly amounts for the entire home. The tool allocates a share. Mortgage principal is not an expense.
4. Direct rental costs
Costs that benefit only the rental activity, such as ads, screening, or paint limited to the rented room.
Illustration only
Fill in rent and square footage to see a rough allocation.
Market context
Check local rent comps
An allocation sketch does not tell you whether the rent itself is in range for your area. Compare nearby rental data before you treat the income figure as typical.
Check rent data with RentCastPartner link. RoomRental.com may earn a commission at no extra cost to you.
Want the concepts behind the numbers?
Read the IRS-grounded overview of income, allocation, depreciation, records, and a future home sale. Then take your facts to a tax professional.
Read the tax deductions guideWhat this estimator is doing
If you rent part of the home you live in, IRS Publication 527 says expenses connected with producing rental income may be deductible, and that a reasonable method may be used to divide a whole-home expense. Square footage and number of rooms are two common methods.
This tool multiplies your whole-home totals by that percentage, then adds costs you mark as rental-only. It stops there. It does not decide what is deductible, capitalizable, or limited.
Please have a CPA or enrolled agent review your situation. This page does not calculate a filing number. It does not account for depreciation, passive-loss limits, land versus building, state tax, below-market rentals, short-term use, separate dwelling units, or your complete tax picture.
The two allocation methods
| Method | How this tool uses it | Watch-outs |
|---|---|---|
| Square footage | Rented-room square feet divided by whole-home square feet | Measure consistently. Shared areas are not automatically extra rental space. |
| Room count | Rooms rented divided by rooms in the home, if you enter both | A large primary suite and a small bedroom are not equal rooms in real life. |
The illustration total uses the square-footage method. If you fill room counts, the room-count percentage and a second illustration appear so you can see the difference. Direct, shared, capital, and personal expenses can still receive different treatment on an actual return.
What is left out on purpose
- Depreciation. Residential rental real estate is generally recovered over 27.5 years. Land is not depreciable. Basis and conversion-date value are not collected here.
- Land versus building. Only the building portion of basis is depreciable. This tool does not split land.
- Passive-activity limits. Rental losses are often limited. A positive or negative illustration is not a usable loss.
- State tax. State rules can differ from the federal overview.
- Improvements and furniture. A renovation or asset may need to be capitalized rather than deducted in the year paid.
- Mortgage principal. Only interest may be relevant, and only after allocation.
IRS Publication 523 also explains that depreciation allowed or allowable can affect a later home sale, even if you did not claim every deduction. Read the room rental income and deductions guide before you treat rental use as a simple extra line on a return.
Keep records from the first day
- The signed room rental agreement and a log of rent received
- Your written allocation method, measurements, and supporting notes
- Mortgage interest, property tax, insurance, and utility statements
- Receipts labeled as direct rental, shared, personal, repair, or improvement
Common questions
Does this calculator tell me how much I can deduct?
No. It produces an educational illustration of how square-footage or room-count allocation can split whole-home costs. It is not a filing number, not taxable income, and not tax advice.
Which allocation method does the IRS mention?
IRS Publication 527 says a reasonable method may be used. Square footage and number of rooms are two common methods. The facts of the home and the expense can change which method is reasonable. For some utilities, another method (such as the number of people using the service) may also be reasonable.
Why is depreciation left out?
Depreciation depends on basis, fair market value at conversion, land versus building, placed-in-service date, and recovery period. This tool does not collect those facts and does not estimate depreciation.
Are direct rental costs treated differently from whole-home costs?
In this sketch, advertising, screening, and work that benefits only the rented room are treated as rental-only. Mortgage interest, property tax, insurance, and utilities are treated as whole-home costs and then allocated. Your tax professional may sort a cost differently.
Primary IRS sources
Educational information only. RoomRental.com does not provide tax, legal, accounting, appraisal, or financial advice. IRS publications change. Confirm the current rules and your own facts before filing.