How the numbers work
Methodology
Every figure on DealScope — and in every embedded calculator or API response — is produced by deterministic arithmetic. The same inputs always yield the same output. A language model may write prose, but it never invents a number. This page states exactly what we assume and why.
The financial model
The buy-to-let forecast is pure arithmetic, offered at three depths depending on plan. The public API and embed widget run the Advanced model.
Basic (Free)
Year-one snapshot: costs, cash required, yields and cashflow.
Advanced (Professional)
10-year projection with rent growth, capital growth and cumulative ROI.
Complete (Portfolio)
Everything, plus rate stress-tests, voids, tax, IRR and exit modelling.
Honest defaults, locked
When our calculator is embedded on someone else’s website or called through the API, four assumptions are fixed and cannot be tuned to make a deal look better than it is. They can only ever make it look more conservative.
Void allowance
Rent is never modelled at 100% occupancy. We hold a minimum of 2 weeks of voids per year, because every property sits empty between tenancies.
Management fee
A letting/management cost of at least 10% of gross rent is always deducted. If an agent states a higher fee, we use theirs — we never model below the floor.
Stamp duty
SDLT is auto-computed at England’s additional-property rates from the price (plus the 2% non-resident surcharge where it applies). It is never taken from user input and never zeroed.
Growth caps
Rent and capital growth are each capped at 5% per year, so a calculator can’t compound an implausible appreciation rate into a flattering headline.
DealScore
A DealScore is a 0–100 rating computed by arithmetic from a unit’s own numeric facts — never invented by a language model. Six factors sum to 100, and the design rules are deliberately conservative. An embedded calculator shows a DealScore only when it is pointed at a real DealScope listing; for a generic calculation it is withheld rather than faked.
- •Yield dominates — it is the investor’s actual return.
- •Costs can only subtract points, never add them — no inverted incentive.
- •Genuine benefits (buyer incentives, priced below market) can only add points, and are withheld when absent, so a plain listing is never dragged below its own baseline.
- •Missing inputs are withheld, not scored as zero — a sparse or new listing is not penalised for lack of data.
- •No location/postcode “quality” term — we never launder area affluence into a score.
- •Coarse by construction — every component is banded, so the score can’t manufacture single-point precision the data can’t support.
Embed & API
Pro-tier agents can embed the calculator with a single <iframe> or call POST /api/v1/breakdown with a Bearer key. Every response carries ameta.assumptions block listing the locked defaults above, so the honesty travels with the numbers. Manage keys from your agent dashboard.
All figures are estimates for illustration only and are not financial, tax, or investment advice. Verify independently before investing.