Allow user to select calculation method:
-Simplified expenses, based on the hours of business use per month/flat rate.
-User enters annual totals (or uploads receipts/invoices) for domestic bills (heating, electric, mortgage interest, home insurance, repairs, cleaning, rent, council tax etc) and also enters the details of number of rooms in the house and the number of rooms used for the business, then the number of total hours each room is used for during a month, then the number of business hours the room is used for.

the tool will suggest a reasonable allowance claim, which can be recorded as a 'cost' item in the cost inbox.

similar to this: https://www.gosimpletax.com/work-from-home-allowance-calculator/