The UK Property Calculator Most Investors Wish They Had Earlier
The UK Property Calculator Most Investors Wish They Had Earlier
Most property deals don’t fail because they’re bad.
They fail because someone didn’t actually run the numbers properly.
And no — a quick “£300/month looks good” on the back of a napkin isn’t analysis.
That’s gambling.
The problem nobody wants to admit
Most UK investors are still:
guessing yields
ignoring real costs
underestimating voids
overestimating rent
and completely missing tax impact
Then they wonder why a “great deal” turns into stress, refinancing issues, or zero cashflow.
You don’t have a deal problem.
You have a clarity problem.
Why I built this calculator
I didn’t build this to look fancy.
I built it because I was tired of seeing:
spreadsheets that break
overcomplicated tools no one actually uses
and “deal analysis” that ignores reality
So this tool does one job:
👉 Tell you fast if a deal is worth your time — or not.
What it actually does (no fluff)
This isn’t just a rent vs mortgage calculator.
It’s built for real UK investing scenarios:
🔹 BTL
Monthly & annual cashflow
Gross yield
Cash-on-cash return
Break-even occupancy
🔹 BRRR
Cash left in deal
Money recycled
Real ROI (not fantasy ROI)
🔹 HMO
Cashflow
ROI
Yield
Estimated commercial valuation
Plus:
Stress testing (rates, rent, costs)
Export to CSV / Excel / PDF
Save & load deals
Investor-ready summaries
Built-in lead capture
This isn’t theory.
It’s based on real-world structures and deal analysis frameworks
Web version vs Desktop (this is important)
You’ve got two ways to use it:
🌐 1. Web version (fast screening)
👉 https://www.marcinsakowski.com/webcalculator
(or via Resources → Web Calculator)
Use this when:
you’re on the go
analysing Rightmove deals quickly
filtering opportunities fast
💻 2. Windows EXE (serious work)
Download directly from the calculator page.
Use this when:
you’re packaging deals
presenting to investors
building a pipeline
exporting reports
This is the full version — local save, full workflow, proper outputs.
The uncomfortable truth
Most people don’t need more deals.
They need:
better filtering
faster decisions
brutal honesty in numbers
Because here’s what happens:
👉 Bad deal + optimism = stress
👉 Average deal + leverage = risk
👉 Good deal + discipline = wealth
This tool is built to force that discipline.
How to actually use it properly
Don’t just plug numbers in and hope.
Do this:
Run the deal
Stress test it (rates +2%, rent -10%)
Check break-even occupancy
Look at cash left in deal
Ask: would I still do this if it got worse?
If the answer is no — it’s not a deal.
Where most investors still mess up
Even with tools like this, people:
ignore maintenance
forget management
skip void assumptions
underestimate refurb
chase yield instead of sustainability
No calculator can fix bad judgement.
But it can expose it.
Use it properly or don’t bother
This isn’t for:
“I just want a quick number” people
TikTok investors chasing hype
spreadsheet collectors
This is for:
operators
serious investors
people building long-term portfolios
Try it yourself
👉 Use the web version:
https://www.marcinsakowski.com/webcalculator
👉 Or go deeper with the desktop version (download on the page)
Final thought
The difference between amateurs and professionals isn’t deals.
It’s how they analyse them.
Most people guess.
Professionals model.
Now you’ve got the tool.
Use it properly.
