Every deal gets judged.
Yours either stacks — or it doesn't.
StackCheck is the rubber stamp for UK property deals. Feed it the numbers — it runs stamp duty, lender stress tests and real cashflow, then thumps an honest verdict on the paperwork. Buy-to-let, flip, or BRRR.
⚿ RUNS IN YOUR BROWSER — YOUR FIGURES NEVER LEAVE YOUR MACHINE
Three strategies. One verdict.
Most deal calculators flatter the deal. StackCheck uses deliberately conservative screening thresholds — the kind experienced investors use — so a "Stacks" stamp actually means something.
Buy-to-Let
The full monthly picture, not just gross yield.
- Cashflow after management, maintenance, voids & insurance
- Lender ICR stress test (125% / 145%)
- Section 24 tax estimate — personal vs limited company
- Break-even rent, cash-on-cash, net yield
Flip
Profit after every cost people forget.
- SDLT surcharge, bridging interest & arrangement fees
- Holding costs over the full project length
- Profit-on-GDV margin check (the 15% rule)
- Annualised return on your cash
BRRR
How much of your cash actually comes back out.
- Capital released at refinance vs money left in
- Post-refinance cashflow & stress test
- % of your cash recycled
- Equity created by the refurb
How it works
No account, no spreadsheet wrestling, no "enter your email to see results".
Enter the deal
Price, rent, refurb, mortgage terms. Sensible UK defaults are pre-filled — change what you know, keep the rest.
Get stamped
STACKS, TIGHT, or DOESN'T STACK — with the exact reason why, and every metric a lender or sensible investor would check.
Compare & keep
Save deals side by side, export them to a file you own, and print a clean report for your broker or business partner.
Built for the UK. Current for 2026.
Generic calculators get UK deals wrong. StackCheck is built on the rules that actually apply here.
2026 SDLT bands
England & NI rates including the 5% additional-property surcharge and first-time buyer relief, calculated band by band.
Lender stress testing
Every rental deal is tested the way a lender tests it — ICR at a stressed rate — so you're not surprised at mortgage application.
Section 24 aware
Tax estimates reflect the mortgage interest rules for personal ownership vs a limited company, so the after-tax picture is realistic.
Rates change. Rules change. Stay stamped-up.
One short email when something changes that affects your numbers — Budget SDLT changes, rate moves, new StackCheck features. No spam, unsubscribe any time.
Questions people ask
Is StackCheck really free?
Yes — the full analyser is free with no signup. The calculations run in your browser, so your figures are never uploaded anywhere. If we add paid extras later (saved portfolios, PDF reports), the core analyser stays free.
Which stamp duty rates does it use?
England & Northern Ireland SDLT rates in force for 2026, including the 5% additional-property surcharge and first-time buyer relief. Scotland (LBTT) and Wales (LTT) use different systems — don't rely on these figures there. Always verify with HMRC's calculator before exchange.
What's the ICR stress test?
Buy-to-let lenders check that monthly rent covers 125–145% of the mortgage payment calculated at a stressed rate (typically your pay rate + 2%). Fail it and most lenders cap your loan below the LTV you wanted. StackCheck runs this on every rental deal.
Is this financial advice?
No. StackCheck does arithmetic on the assumptions you enter — it can't verify your rent estimate or end value, and it isn't financial, tax or investment advice. It's a screening tool: it tells you whether a deal is worth deeper due diligence.