Lettfolio’s Deal Analyser turns the headline numbers from a property listing into a clear buy-to-let assessment: the yields, the costs, the monthly cashflow, the return on your cash, and a single 0–100 Deal Score. This page sets out exactly how those numbers are produced and where the limits sit — because a score is only useful if you can see what’s behind it.
The figures we calculate
- Gross yield — annual rent ÷ purchase price.
- Net yield — (annual rent − running costs) ÷ purchase price.
- Stamp duty (SDLT) — England & Northern Ireland bands effective 1 April 2025, including the 5% additional-property surcharge that applies to most buy-to-let purchases. (Scotland’s LBTT and Wales’ LTT differ and aren’t covered.)
- Mortgage cost — interest-only (
loan × rate) or repayment (standard amortisation over the chosen term). - Monthly cashflow — rent − running costs − mortgage payment.
- Cash-on-cash ROI — annual cashflow ÷ total cash invested (deposit + stamp duty + buying fees + refurb).
- Rent cover (ICR) — rent ÷ mortgage payment, the ratio buy-to-let lenders use to stress-test affordability.
The Deal Score
The Deal Score is a weighted figure out of 100, built from four factors. It rewards genuine investment fundamentals — yield, positive cashflow, return on cash, and comfortable lender cover — rather than a single headline number.
| Factor | Weight | Full marks when… |
|---|---|---|
| Gross yield | 30 | 8% or higher |
| Monthly cashflow | 30 | positive and ≥ 30% of the rent |
| Cash-on-cash ROI | 25 | 10% or higher |
| Rent cover (ICR) | 15 | 1.45× or higher |
The verdict is then: 70+ a strong deal, 45–69 fair (worth negotiating), and below 45 weak (be cautious). The breakdown is always shown so you can see which factor is helping or hurting.
Default assumptions (all editable)
To give you an instant result we start from sensible defaults, which you can change for any deal:
- Deposit: 25% of the price.
- Mortgage: 5.5% interest-only.
- Running costs: 25% of rent (management, maintenance, insurance and void allowance).
- Buying fees: £2,000 (legal, survey and similar).
Known limitations
- The analysis is based only on the figures you enter. It does not value the property or pull comparable sold prices — that comparable-evidence engine is on our roadmap.
- It doesn’t model capital growth, tax on rental profit, or your personal financial circumstances.
- Rates, fees and rents are your estimates — always confirm with real mortgage quotes and local rental evidence before committing.
Score your next deal free
Run the numbers on any buy-to-let with Lettfolio's Deal Analyser — yields, cashflow, ROI and a 0–100 Deal Score.
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