Why most deal calculators are doing you a disservice
Most online property calculators are designed to make a deal look good. You enter the asking price, an optimistic rent figure, and a 75% mortgage — and the spreadsheet spits out a yield that makes your heart race.
The problem? Those calculators almost never include the things that quietly eat your returns:
- Voids (a month a year is a sensible starting assumption, not a worst-case)
- Management fees (8-12% of rent for full management)
- Maintenance (1-2% of property value annually — yes, every year)
- The cost of your own time (you are not free labour)
- Stress-tested interest rates (your 5% mortgage isn't a 5% mortgage forever)
A 5-minute reality check you can do on any deal
Next time a deal lands in your inbox, before anything else, ask yourself:
1. What would I sell this for tomorrow morning?
Not what the agent says. Not what you 'hope' it'll be worth. The number a buyer would actually pay you, today, in the current market, if you needed cash by Friday.
2. What's the true monthly cost of ownership?
Mortgage + 10% of rent for management + 1/12 of (property value × 1.5%) for maintenance + a month-a-year void allowance.
3. What happens if rates go up 2%?
Does the deal still work? Or does it slip into the red?
4. Who is the tenant?
Not 'a tenant'. Who specifically. A nurse near a hospital? A family near a school? A student near a campus? If you can't picture them in 30 seconds, the demand might not be as solid as you think.
5. Would I still buy this if no one ever congratulated me?
The most underrated question in property. A surprising number of 'deals' only make sense as social signalling.
What to do with this
If a deal survives all five questions — then dig deeper. Get the search done, view it twice, talk to the local agents about void rates.
If it doesn't — you've just saved yourself months of stress, often six figures, and a hard conversation with your partner. That's a good five minutes.