Strategy calculator
Buy to Let Calculator UK -- Free Yield & Cashflow
The Buy to Let calculator computes gross yield, net yield, monthly cashflow, and ROI on a single UK rental property. It is built around current UK rules -- Section 24 mortgage interest treatment, the 3% additional-property SDLT surcharge, and the EPC C requirement coming for new tenancies. No login. No paywall. Open it, run the numbers, decide.
What does the BTL calculator measure?
Four numbers, in order of importance for UK BTL underwriting. Gross yield is annual rent divided by purchase price -- a quick screen for whether a deal is even worth a second look. Net yield is annual rent minus all running costs (management fee, insurance, maintenance, ground rent, service charge, void allowance) divided by total purchase cost including SDLT and legals. Net yield is the figure that matters; it strips out the gimmickry of headline rents that get eaten by service charges on apartments.
Monthly cashflow is rent received, minus running costs, minus mortgage payment. This is the actual cash hitting your account each month. Cashflow can be negative on a deal that looks fine on yield -- this is why both numbers matter. The calculator separates personal-name BTL (Section 24 applies) from limited company BTL (no Section 24, but corporation tax on profits and dividend tax on extraction).
ROI on capital invested is annual cashflow plus first-year capital growth (if you choose to include it), divided by total capital deployed (deposit, SDLT, legals, refurb, void during renovation). This is what lets you compare a UK BTL against alternative investments on the same metric, rather than getting trapped in yield-versus-yield comparisons.
UK BTL context -- two rules that change everything
Section 24. Fully phased in since the 2020/21 tax year, Section 24 of the Finance Act 2015 removed mortgage interest as a deductible expense for personal-name BTL. Instead, you get a 20% basic-rate tax credit on interest paid. For higher-rate (40%) and additional-rate (45%) taxpayers, this materially increases the effective tax on rental profit -- and on highly geared properties can push you into a tax bill on a deal that loses money in cash terms. Limited company structures are unaffected (interest is a normal P&L expense), which is why most new BTL purchases since 2020 have been through limited companies.
EPC C by 2028. The previous government's draft proposal -- maintained in principle by the current administration -- is that all new BTL tenancies will need an EPC rating of C or above by 2028, extending to all existing tenancies by 2030. Lenders are already pricing this in: some withdraw products on F and G properties entirely, and most apply an EPC-band differential to their best rates. When buying, budget any insulation or heating upgrades needed to reach EPC C into your refurb costs -- it is no longer optional.
Reading the output. As a rule of thumb, a single-let BTL is "good" if gross yield is 5%+ and net yield is 3%+. In London and the South East these thresholds are rarely met and investors lean on capital growth. In the Midlands, North and Wales, 7-9% gross yield is achievable and the case for cashflow-led investing is stronger. Always compare net yield, not gross.
Common BTL mistakes
- 1 Quoting gross yield as the headline number. 8% gross on a leasehold flat with a £3,500 service charge is probably 4-5% net. The calculator computes both; always quote the net figure.
- 2 Forgetting void allowance. Even a well-tenanted property sees 1-2 weeks vacant per year between tenancies. Model 4% void as a baseline (more for student or HMO). Otherwise your "real" yield is overstated.
- 3 Modelling with today's mortgage rate, not the stress rate. Lenders stress at the higher of pay rate or 5.5%. If your deal does not cashflow at 5.5%, you will struggle to refinance when the fix ends.
Underwrite a BTL in 60 seconds
Open the calculator free, or sign up to Propreneur to save the analysis against a real property and run the same numbers through Carina AI for a sense check.