Short answer: add up everything you put in (price, stamp duty, refurbishment and fees), take away the new mortgage after revaluation, and what is left is the money still tied up in the deal. Then check the rent covers the new mortgage with room to spare.
Worked example
Illustrative figures for a property bought as an additional home in England.
| Line | How it's worked out | Amount |
|---|---|---|
| Purchase price | £120,000 | |
| Stamp Duty Land Tax | 0% standard rate up to £125,000, plus the 5% higher rate for additional properties on the whole price | £6,000 |
| Refurbishment | £25,000 | |
| Fees (legal, survey, bridging costs) | Example | £6,000 |
| Total money in | £157,000 | |
| Revaluation after works | Example | £180,000 |
| Refinance at 75% loan to value | £180,000 × 75% | £135,000 |
| Money left in the deal | £157,000 − £135,000 | £22,000 |
| Rent | £1,050 a month | |
| New mortgage interest | £135,000 at 5.5% interest-only | £618.75 a month |
| Rent less mortgage interest | Before other costs and tax | £431.25 a month |
SDLT rates from GOV.UK (England and Northern Ireland). Scotland and Wales have different taxes. Check your own figure with HMRC's calculator or the free Stamp Duty Calculator. Lenders often have a minimum ownership period before refinancing, and valuations are not guaranteed.
Three checks before you buy
- Is the end value realistic? The whole deal depends on the revaluation. Look at sold prices for finished, similar homes nearby.
- Does the rent pass the lender's stress test? Buy-to-let lenders test rent against a stressed interest rate, so a deal can work on paper and still not refinance to 75%.
- What if the refurb runs over? Every £1,000 over budget is £1,000 more left in the deal.
Tools for BRRR numbers
| Option | Cost (as published 18 October 2026) | What it does |
|---|---|---|
| Spreadsheet | Free | Flexible, but you build and check the formulas |
| PropertyData Deal Analyser | Included in plans from £15 a month + VAT | Appraises buy-to-let and BRRR deals with a score, alongside market data |
| Property Clues BRRR Calculator | £19 one-off (or in the £129 Investor Pro bundle) | Money in, bridging costs, refinance, money left in, equity released and cashflow |
Questions people ask
How do you calculate money left in a BRRR deal?
Add the purchase price, stamp duty, refurbishment and fees, then subtract the new mortgage after revaluation. In the worked example £157,000 in, less a £135,000 refinance at 75% of £180,000, leaves £22,000 in the deal.
How much stamp duty is there on a £120,000 buy-to-let?
In England and Northern Ireland, an additional residential property bought for £120,000 pays the 5% higher rate on the whole price, so £6,000, because the standard rate is 0% up to £125,000. Check GOV.UK or HMRC's calculator for your case.
Is there a BRRR calculator without a subscription?
Yes. The Property Clues BRRR Calculator is £19 one-off and includes bridging costs, refinance and money left in. A free preview with example figures is available.