The $5 flat rate replaces the expense split
The simplified method is a flat $5 per square foot of qualifying space, and that is its whole appeal: no allocating mortgage interest, utilities, insurance or repairs between the office and the rest of the home. IRS Publication 587 states the rate directly, and the page applies it without asking for a single receipt.
The alternative is the regular method, which takes the business percentage of actual home expenses. That route can be worth more in a house with a large mortgage and high utilities, but it requires keeping every bill and working through the allocation, and none of it happens on this page.
Because the two methods are alternatives for the same home in the same year, this page is deliberately narrow. It prices the shortcut, prints the area, rate and months behind the answer, and leaves the comparison between methods to a Schedule C prepared with the actual numbers.
The 300-square-foot cap
The allowable area is the smaller of the square footage you use for the business and 300 square feet. A 400-square-foot office still deducts on 300, which at $5 for a full year is $1,500 rather than $2,000.
The area field accepts any figure from zero upward, and the cap is applied before the multiplication rather than to the result, so overshooting the limit produces the same answer as entering exactly 300. That makes the cap easy to see: the hero reports the allowable area next to the rate and the months.
There is only one area field, because the page prices one qualifying space. If two people share a home and split the office, or a room is used by two separate businesses, the area has to be divided before it is entered - the page has no field that would let it make that allocation for you.
Part of a year counts proportionally
If the space qualified for only part of the year, the deduction is prorated by months: allowable area times $5 times the months of business use divided by twelve, rounded to the cent. A 240-square-foot office used for eight months is $800 rather than $1,200.
The months field is clamped between 0 and 12. A desk that became an office in July counts six months, not twelve, and entering zero leaves the deduction at $0.00 while the note still describes the proration that produced it - a zero that comes from the calendar rather than from a missing input.
What the page does not model is an area that changes during the year. If you moved the office into a larger room in September, the honest calculation is two periods with two areas, and this page can only price one of them at a time; run it twice and add the results.
Regular and exclusive use is the gate
The space has to be used both regularly and exclusively for business. The corner where you occasionally answer email on a laptop is personal space, not an office, and a room that doubles as a guest bedroom fails the exclusive test even if the desk is used every day.
Two rules sit outside the arithmetic and are worth naming. Day care provided in the home follows its own rules rather than the $5 shortcut, and the simplified deduction cannot exceed the business income from the home use after unrelated business expenses - a home office can reduce profit, but it cannot create a loss on its own. Neither limit is computed here.
The deduction is a business expense on Schedule C for a sole proprietor, not an itemized deduction on Schedule A, which is why it never enters the standard-versus-itemized comparison. Keep a note of the area and the months; that record is what makes a small, boring deduction easy to defend if a question ever arrives. An estimate, not a return, and not tax advice.
What the simplified method trades away
The $5 shortcut is not a discount version of the same deduction; it is a different deduction. Take the default 150 square feet for 12 months: $750 under the simplified method. Itemize instead and the same room might carry $1,400 of real costs — a third of the electric bill, a third of the insurance, the internet, part of the rent — but it also brings depreciation, and depreciation is recaptured at 25% when the house is sold. On a $300,000 home with 10% business use that is $3,000 of depreciation a year, and the recapture is a bill the simplified method never creates.
Two more differences decide the choice. The simplified method cannot create or add to a loss: if the business already runs at a loss, the $750 may not be deductible this year, while the actual-expense method allows some of it to carry forward. And the simplified method is per square foot, not per cost, so a home office in an expensive city and one in a cheap one produce the same number — the deduction is indifferent to what the space actually costs you.
Danfio