Home Office Share Calculator
Apportion household running costs to a home working space by floor area and days used, for expense records and cost awareness.
💼 Are you a real estate agent or broker? Send this calculator to your buyers on your own branded listing page — every enquiry comes straight to your WhatsApp. Create free agent page →Working from home moves part of the cost of running a household into the cost of running a business. The usual method apportions by floor area — the working room as a share of the total — and then by time, since a room used five days a week is not a business space on the other two.
How much of this is deductible, and on what basis, is set by tax law and differs sharply between countries. This calculates the apportionment; whether and how you can claim it is a question for a local accountant.
The apportionment
Area share = office area ÷ total floor area. Multiply household running costs by that share, then by the days used out of seven. Running costs typically mean heating, electricity, water, insurance, maintenance and any interest or rent — not capital repayments.
Worked example
A 120 square foot office in a 1,500 square foot home is 8% of the floor area. Against 14,000 of annual running costs that is 1,120 by area. Used five days a week, the time-apportioned figure is 800 a year, or about 67 a month.
This is an apportionment, not tax advice
Countries differ on which costs qualify, whether a flat-rate alternative is available, whether exclusive business use is required, and whether claiming affects capital gains relief on the property. Confirm the treatment locally before relying on any figure here.
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Create your free property pageFrequently asked questions
Which costs can be apportioned?
Generally the running costs of the property — heating, power, water, insurance, maintenance and rent or mortgage interest. Capital repayments are not a cost of running the home, and most systems exclude them.
Does a flat-rate method exist?
Many tax systems offer a simplified per-hour or per-month allowance that avoids apportionment entirely. It is usually lower than the calculated figure but needs no records, which suits smaller claims.
Can claiming affect selling my home?
In some jurisdictions claiming a room as exclusively business use can reduce main-residence relief on that proportion when you sell. This is a real risk worth asking an accountant about before choosing an apportionment basis.