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
A 20-second sign-up with just your email, then no spreadsheet wrestling — your deal figures are worked out in your browser and never uploaded.
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 and print a clean one-page report for your broker or business partner — no spreadsheet wrestling required.
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.
Learn the maths before you buy.
Plain-English guides to the numbers that actually decide a UK deal — no "top 10 tips" filler.
Does your BTL stack?
Stamp duty, stress test, cashflow and tax — the full walk-through to an honest verdict.
GUIDEThe lender stress test
Why the ICR test caps your loan before cashflow ever matters — and how to pass it.
GUIDESection 24 explained
How the mortgage-interest rules quietly turn a higher-rate landlord's profit into a loss.
Free to check. Pro to run a pipeline.
Checking a deal is free — sign up with your email, enter the numbers, get the verdict. Pro is the layer a serious buyer needs before committing real money: how the deal breaks, and the loan a lender will actually give.
Stress-test grid
See the exact point a deal breaks — rate rises, rent drops, doubled voids — before the market finds it for you.
Lender reality check
The biggest loan the ICR test will actually allow, and whether your deal clears it — before you waste a mortgage application.
Every new tool first
Pro members get new calculators and features as they land, and a say in what gets built next.
14-day no-quibble refund · Cancel any time · Checking deals is always free
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 free?
Yes. You create a free account with just your email — no password, no card — then get the full verdict and core figures. The calculations run in your browser, so your deal figures are never uploaded anywhere; only your email is stored. StackCheck Pro is a paid upgrade for people running a pipeline: deeper stress-testing, the real loan a lender will offer, and (soon) a saved, alerted portfolio.
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.