Portfolio mortgage calculator and stress test
Enter each rental property's value, mortgage and rent to see portfolio rent cover, loan-to-value and cash flow at a stressed rate. The calculator is coming soon.
Reviewed by David Sampson, Founder & Director · Created 20 October 2026 · Last reviewed 20 October 2026
How a portfolio mortgage calculator works
A portfolio mortgage calculator adds up the value, mortgage, monthly payment and rent of every rental property a landlord owns, then shows the overall loan-to-value, rent cover and monthly cash flow. A stress test repeats the sums at a higher interest rate entered by the user, to show how the portfolio would cope if rates rose.
The figures are estimates based on the inputs entered. Lenders use their own stressed rates, cover ratios and criteria, so a calculator result is a starting point rather than a decision.
Stress testing a portfolio
Stress testing a portfolio means checking whether the total rent would still cover the total interest, with a margin, at a higher rate than today's. Lenders do this when a portfolio landlord applies for new borrowing. Seeing which properties fall short at the stressed rate shows where refinancing or rent reviews would help most.
Including running costs such as letting fees, repairs and voids gives a fuller view of cash flow than the lender's rent test alone.
Using the results
The results can help a landlord prepare a property schedule and cash flow forecast for a lender, or decide whether releasing equity from one property to buy another would leave the portfolio within a lender's limits. How lenders assess portfolios, including the documents they ask for, is in the guide to portfolio landlord rules.
Tax, stamp duty and fees need working out separately.
Frequently asked questions
What does a portfolio stress test show?
Whether the total rent covers the total interest, with a margin, at a higher interest rate.
Do lenders stress test my whole portfolio?
Lenders following portfolio rules look at the whole portfolio when a landlord with four or more mortgaged properties applies.
Is the result a lending decision?
No. It is an estimate based on the figures entered. Lenders apply their own criteria.
Can I enter my own stressed rate?
Yes. The finished calculator will use rates entered by the user.
Can it include running costs?
Yes. The finished calculator will allow letting fees, repairs and voids to be included.
Does it work for company portfolios?
Yes. The sums are the same for properties held personally or in a company.
Important: Your home may be repossessed if you do not keep up repayments on your mortgage. Information on this page is for general guidance only and does not constitute financial advice.Always verify details directly and seek independent advice before making financial decisions.