Buy to let investment calculator
The whole deal on one page: what it costs to buy, what it makes each month, how it holds up when rates rise, and what it returns over the years you plan to own it.
How this is calculated
Stamp duty is worked out on the slice basis using the England and Northern Ireland bands, plus the 5% higher rate on the whole price for an additional property or a company purchase, and 2% more for a non-resident buyer.
The cash you put in is the deposit plus stamp duty, fees and any refurbishment. Monthly cash flow is rent after the void allowance, less the agent fee, running costs and mortgage payments. The agent fee is charged on rent actually collected.
Net yield is income before finance divided by the total cost including purchase costs, so it describes the property. Return on cash divides cash flow after finance by the cash you put in, so it describes your money.
The projection grows rent, costs and value by the rates you enter. At the end the property is sold, selling costs and the remaining mortgage are paid off, and the internal rate of return is worked out on the yearly cash flows including the sale. The equity multiple is everything you got back divided by what you put in.
Rates and assumptions used
| SDLT up to £125,000 | 0% |
| £125,001 to £250,000 | 2% |
| £250,001 to £925,000 | 5% |
| £925,001 to £1.5m | 10% |
| Above £1.5m | 12% |
| Additional property surcharge | 5% of the whole price, from £40,000 |
| Non-resident surcharge | 2% of the whole price |
| Tax on rental profit | not included |
Statutory rates last checked July 2026. Source: HMRC and gov.uk.
Worked example
A £200,000 additional property carries £11,500 stamp duty: £1,500 on the slice from £125,000 to £250,000 plus the £10,000 surcharge. With £3,000 of fees and a 75% interest-only mortgage at 5%, you put in £64,500. Let at £1,100 a month with a 4% void allowance, a 10% agent fee and £1,450 of running costs, it produces £9,955 a year before finance, or £2,455 after £7,500 of interest: £205 a month and a 3.8% return on your cash. Tested at 7% the same deal loses about £45 a month.
Common questions
Why is my return on cash so different from the yield?
Yield describes the property and ignores how you paid for it. Return on cash includes the mortgage, so borrowing more raises it when the rent covers the interest comfortably and cuts it hard when it does not. The grid under the calculator shows that trade-off.
What stress rate should I use?
Use a rate you could realistically face when your current deal ends. Lenders test new buy to let loans at their own stressed rate, often around 5.5% or more, and expect rent to cover the interest by 125% or 145%.
Does this include tax?
No. Individual landlords cannot deduct mortgage interest from rental profit and receive a 20% tax credit instead, so a higher rate taxpayer can owe tax even when cash flow is small. Companies are taxed differently. Treat the cash flow here as before tax.
Is IRR the right measure?
It is the most complete single figure because it accounts for timing: money back sooner is worth more. It depends entirely on the growth and exit assumptions, so compare it alongside the year one cash flow rather than on its own.
Maximum offer and BRRR calculator
Work back from the done-up value to the most you can pay and still get your money out.
Buy to let borrowing calculator
The most a lender will lend on loan to value and rental cover, and which one limits you.
Rental yield calculator
Gross and net yield after voids, agent fees and running costs.