One dated entry per dollar, attached to the property it came from
Amount, date, direction, property. Four things per transaction, and the receipt attached to the entry rather than filed somewhere else. Do that consistently and tax season stops being an archaeology project.
The furnace repair. The plumber's invoice. Rent arriving. Anything moving in or out because you own a rental.
Why the receipt has to live on the entry
A number without a document is a claim. If you are asked to support $2,400 of repairs, you need the amount, the date, and the invoice that proves it, together.
The common failure is not missing receipts, it is receipts that exist but cannot be matched to a line. A shoebox of paper and a spreadsheet of numbers are two records that each need the other, and reconciling them a year later takes an evening you will resent.
Tag to the property, and the unit when it is honest
Costs that belong to the whole address stay at the property level: tax, insurance, roof, furnace. Costs caused by one tenancy go to the unit: the fridge in Unit 2, the repaint after a move-out.
Do not split a shared cost across units to make it look tidy. An invented allocation is harder to defend than an honest property-level entry.
Income is a record, not just a total
Rent arriving is a transaction, and the running record of it is your rent ledger. Recording payments as they happen is what makes that ledger persuasive later, because it shows the record was kept contemporaneously rather than assembled after a dispute started.
If a tenant needs proof of a single payment right now, the free rent receipt generator produces a PDF without an account.
What this is not
It is not bookkeeping. You still need an accountant or accounting software for depreciation, mortgage interest splits and the return itself. What this gives that software is a clean, evidenced list of what happened, by property.
In UnitDocs
Open Transactions, click Add Transaction, pick expense or income, enter amount and date, select the property and the unit or lease if relevant, upload the receipt, and save. The entry then shows up under that property and, when you tagged one, that unit.