Maximum offer calculator for buy, refurbish and refinance
Start from what the property will be worth once the work is done and work backwards to the highest price that still lets the refinance repay everything you put in.
How this is calculated
The refinance amount is the done-up value multiplied by the refinance loan to value. The maximum offer is the price at which the purchase price, stamp duty on that price, the refurbishment, fees, other costs and the cost of money add up to exactly that amount.
The cost of money is charged on the purchase price plus the refurbishment, at the rate you enter, for the months until the refinance. Stamp duty depends on the price, so the offer is found by searching rather than by a single formula.
After the refinance, cash flow is rent less the agent fee, maintenance and other costs, and interest-only payments on the new loan. The offer ladder shows how far you can go above the maximum offer while leaving one to five years of that cash flow in the deal.
Lenders also cap a refinance by rental cover. The calculator checks the loan against 145% cover tested at 5.5%, a common test for higher rate taxpayers, and warns if the rent would not support the full loan.
Rates and assumptions used
| SDLT up to £125,000 | 0% |
| £125,001 to £250,000 | 2% |
| £250,001 to £925,000 | 5% |
| Additional property surcharge | 5% of the whole price, from £40,000 |
| Rental cover check | 145% at 5.5% |
Statutory rates last checked July 2026. Source: HMRC and gov.uk.
Worked example
A property worth £200,000 once refurbished, refinanced at 75%, returns £150,000. Take off £25,000 of works and £6,000 of fees and other costs, allow for six months of money at 9% a year, and the most you can offer and still take everything out is about £107,650. At that price stamp duty with the surcharge is £5,382 and the cost of money £5,969. With £1,000 rent and a 5% refinance, every £1,918 you pay above that leaves a year of cash flow in the deal.
Common questions
What does all money out mean?
That the refinance repays everything you spent buying and refurbishing, so none of your own cash is left in the property. In practice valuations often come in below the hoped-for figure, so many investors aim for some money left in rather than none.
Why does paying more still make sense sometimes?
Leaving money in is fine if the return on it is good enough. If the property makes £3,000 a year after the refinance, leaving £6,000 in is a 50% return on that cash. The offer ladder shows the price for each level.
Will a lender really refinance straight away?
Many lenders want you to have owned the property for six months before refinancing on the new value. Bridging lenders and some specialist lenders work differently. Check with a broker before relying on the timing.
Where does the done-up value come from?
From sold prices of similar, finished properties nearby, not asking prices. The surveyor instructed by the lender decides it, and it is the single biggest risk in this calculation.
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