Updated October 18, 2026. Quick answer: Lines 16 to 22 list the operating expenses of the home: excess mortgage interest and real estate taxes, insurance, rent, repairs, utilities and other costs. Line 23 totals them, line 24 applies the business percentage, line 25 adds last year’s carryover, and line 27 takes the smaller of line 15 or line 26.
Lines 16 and 17: the excess amounts
The captions are “Excess mortgage interest (see instructions)” and “Excess real estate taxes (see instructions)”. For line 16 with the standard deduction, the instructions say “If you are claiming the standard deduction, enter all the home mortgage interest paid for loans used to buy, build, or substantially improve the home in which you conducted business in column (b) of line 16.”
For an itemizer the instructions say “include the excess attributable to the loans used to buy, build, or substantially improve the home in which you conducted business in column (b) of line 16.” The instructions also include a dollar example, which is best read in the instructions themselves. The lines 9 to 11 steps that lead into this are on the lines 8 to 15 page.
For line 17 the instructions say “If you used the Line 11 Worksheet to figure the amount to include in column (a) of line 11, then include the amount from line 11 of the Line 11 Worksheet in column (a) of line 17; otherwise, do not enter an amount on line 17.”
Lines 18 to 22: the everyday costs
Line 18 is captioned “Insurance”, line 19 rent, line 20 “Repairs and maintenance”, line 21 “Utilities” and line 22 “Other expenses (see instructions)”. For rent the instructions say “If you rent rather than own your home, include the rent you paid on line 19, column (b).” They add “If your housing is provided free of charge and the value of the housing is tax exempt, you cannot deduct the rental value of any portion of the housing.”
For line 22: “Include on this line any 2025 operating expenses not included on lines 9 through 21.” Which column to use, direct or indirect, is explained on the lines 8 to 15 page. Related Schedule C lines for rent, repairs and utilities are covered at Schedule C lines 20 to 22 and Schedule C lines 25 and 26.
Lines 23 and 24: total and business share
Line 23 is captioned “Add lines 16 through 22” and line 24 is captioned “Multiply line 23, column (b), by line 7”. Line 7 is the business percentage from lines 1 to 7.
Line 25: carryover from last year
The instructions say “Enter any amount from your 2024 Form 8829, line 43.” If there was no 2024 form: “If you did not file a 2024 Form 8829, then your carryover of prior year operating expenses is the amount of operating expenses shown in Part IV of the last Form 8829, if any, that you filed to claim a deduction for business use of the home.”
The instructions also give a reminder for people who used the simplified method: “If you used the simplified method for 2024 but are not using it for 2025, you may have unallowed expenses from a prior year Form 8829 that you can carry over to your 2025 Form 8829.”
Lines 26 and 27: the allowable amount
Line 26 is captioned “Add line 23, column (a), line 24, and line 25”. Line 27 is captioned “Allowable operating expenses. Enter the smaller of line 15 or line 26”. For amounts above the limit, the instructions say “Figure the amount of operating expenses you can carry over to 2026 by subtracting line 27 from line 26.” Part IV is covered on the lines 37 to 44 page.
Where the number comes from
The amounts come from your own bills and records for the home, the carryover comes from last year’s Form 8829, and the business share comes from line 7. Line 15 comes from lines 8 to 15.
Where it goes next
Line 27 feeds line 28 (caption “Limit on excess casualty losses and depreciation. Subtract line 27 from line 15”) and line 34 (caption “Add lines 14, 27, and 33”). Line 43 later says “Operating expenses. Subtract line 27 from line 26”. See the lines 28 to 36 page for the next part of Part II.
Edition and line numbers
This page reads the 2025 Form 8829, Expenses for Business Use of Your Home and its 2025 instructions, the current files irs.gov served on 2026-10-18. They are the files for the tax year 2025 return, filed in 2026. The form’s own header says “File only with Schedule C (Form 1040).” Check the tax year printed on the form you are filling in and use the line numbers on that year’s form, because a different year’s form can number or word its lines differently.
Common mistakes
- Entering the full mortgage interest on line 16 for an itemizer. The instructions say to “include the excess attributable to the loans used to buy, build, or substantially improve the home”
- Skipping the carryover on line 25. The instructions say “Enter any amount from your 2024 Form 8829, line 43.”
- Deducting rental value of free housing. The instructions say “you cannot deduct the rental value of any portion of the housing.”
Related: Form 8829, Schedule C lines 20 to 22, Schedule C lines 25 and 26, home office deduction, and Form 8829 lines 28 to 36.
Sources
- Instructions for Form 8829, Expenses for Business Use of Your Home (2025): https://www.irs.gov/pub/irs-pdf/i8829.pdf
- Form 8829, Expenses for Business Use of Your Home (2025): https://www.irs.gov/pub/irs-pdf/f8829.pdf
Read from the IRS documents linked above on October 18, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.