Mixed-Use Apportionment Calculator
Apportion a mixed-use building between residential and commercial by value rather than floor area, and see how much the two methods differ.
💼 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 →Mixed-use buildings need their value and costs split between uses for lending, insurance, tax and service charge purposes. The lazy method divides by floor area, and it is frequently wrong by a wide margin, because a square foot of residential and a square foot of retail are rarely worth the same.
Apportioning by value instead usually produces a materially different answer, and it is the basis most lenders and valuers actually use.
The two methods
Apportionment by area divides on floor space alone. Apportionment by value multiplies each area by its own value per unit first, then divides. Where the two uses have different values per unit area — which is almost always — the answers diverge.
Worked example
A building with 4,000 of residential and 2,000 of commercial space is 66.7% residential by area. But at 180 per unit the residential is worth 720,000 and at 90 the commercial is worth 180,000, so residential is 80% by value. Apportioning 30,000 of costs gives 24,000 on the value basis against 20,000 on the area basis — a 4,000 difference.
Which basis applies is set by the document
Leases, insurance policies and tax rules each specify their own method, and they are frequently different from one another within the same building. Check what each document actually says rather than applying one split everywhere.
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Create your free property pageFrequently asked questions
Which apportionment method is correct?
Whichever the relevant document specifies. Leases often mandate floor area for service charge, while lenders and valuers generally work on value. Neither is universally right, and the same building can legitimately use both for different purposes.
Why does it matter?
Because it determines who pays what. On this building the difference is 4,000 a year on 30,000 of costs, and across a long lease that compounds into a substantial sum falling on one side or the other.
Do lenders treat mixed-use differently?
Yes, usually as commercial lending with different rates, terms and loan-to-value limits, particularly where commercial is a large share. The residential proportion often determines which lending category applies, which is why the split matters at purchase.