Buy-to-Let Portfolio Analyser (Pro) United Kingdom

What the buy-to-let portfolio calculator does

The Buy-to-Let Portfolio Analyser gives you one financial picture for a set of rental properties. Instead of working out each flat or house separately and adding them up, you describe one typical property and how many you hold, and the analyser scales it to the whole portfolio. You get total annual rent, total mortgage interest, total running costs, net cashflow and gross yield, with a per-property table showing how a single property contributes to the totals.

This is a Pro tool. The calculation runs on the server, which keeps the full breakdown behind the access gate and lets you export the schedule in a premium report. The maths is simple, so you can reproduce every figure it shows.

How the model works

The analyser treats your portfolio as a group of similar properties. You enter six figures: the number of properties, the average property value, the average monthly rent, the average outstanding mortgage balance, the mortgage interest rate and the monthly running costs per property.

For one property it works out the annual rent (monthly rent times twelve), the annual mortgage interest (outstanding balance times the interest rate) and the annual running costs (monthly costs times twelve). Net cashflow is rent less interest and costs. Multiplying each per-property figure by the number of properties gives the portfolio totals.

Worked example

You own three similar flats. Each is worth £200,000, rents for £900 a month, carries a £150,000 interest-only mortgage at 5.5% and costs £150 a month to run.

For one flat, the annual rent is £900 × 12 = £10,800. The annual interest is £150,000 × 5.5% = £8,250. The annual costs are £150 × 12 = £1,800. Net cashflow is £10,800 − £8,250 − £1,800 = £750.

Across three flats the portfolio produces £32,400 of rent, £24,750 of interest, £5,400 of running costs and £2,250 of net cashflow. The gross yield is £10,800 ÷ £200,000 = 5.4%. The portfolio is worth £600,000 against £450,000 of debt. The per-property table repeats the single-flat figures for each of the three.

Reading the results

The main figure is total annual net cashflow, which tells you whether the portfolio puts money in your pocket each year or takes it out. A positive figure means the rents cover interest and costs; a figure close to zero or negative means the portfolio is finely balanced and exposed to a rate rise or a void period.

Gross yield lets you compare the rental return with other properties or assets, though it ignores costs. Total value and total debt together give a rough loan-to-value position across the portfolio, which matters for refinancing and for how exposed you are to falling prices.

Assumptions and limitations

The model treats every property as identical to the average you enter, so a mixed portfolio is smoothed out. If your properties differ widely, run the tool separately for each group of similar holdings. It assumes interest-only mortgages, with interest on the outstanding balance, and does not model capital repayment.

It includes no tax. It leaves out Income Tax on rental profit and the mortgage interest relief rules, which depend on your personal income and whether you own the properties personally or through a company. It also excludes voids, one-off maintenance, letting fees beyond your stated monthly costs and capital growth. Treat the net cashflow as a pre-tax operating result and confirm your full position with a qualified accountant or mortgage adviser before making decisions.

Using the analyser well

The tool is most useful for testing scenarios. Raise the mortgage rate by a point or two to see how a remortgage would squeeze cashflow. Lower the average rent to model a soft lettings market, or raise the monthly costs for higher insurance and management fees. Running several of these shows how resilient your portfolio is before circumstances force the question.

This is general information only and not financial or tax advice.

About This Buy to Let Portfolio Calculator

Use this Buy to Let portfolio calculator to get an instant estimate based on the figures you enter. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.