What does IRR mean for a buy-to-let?

What goes into property IRR?

• The initial equity deposit.
• Purchase tax, legal costs, initial works and other cash costs.
• Annual rental cash flow after operating expenses, debt service and the selected tax treatment.
• Periodic refurbishment or major repairs.
• Net sale proceeds after selling costs, estimated CGT and repayment of the remaining mortgage.

The year in which each amount occurs matters. Receiving £10,000 next year contributes more to IRR than receiving the same £10,000 much later.

Why can IRR be positive when annual cash flow is negative?

IRR measures the full investment rather than one year. A repayment mortgage may build equity through principal repayments. The property may also be assumed to sell for more than it cost. Those future benefits can outweigh negative annual cash flow in the mathematical return.

That does not make negative cash flow harmless. The owner must still fund it, and the positive IRR may depend on an uncertain sale price.

Why the exit assumption matters so much

A large portion of property value is often realised on sale. If the forecast IRR changes substantially when the exit price is reduced by 10%, the investment is exit-sensitive. Our calculator displays that downside directly.

Levered and unlevered return

When a mortgage is used, the property IRR is a return on the investor’s equity after debt payments. This is a levered return. A benchmark fund shown without borrowing is unlevered. Comparing them remains useful, but the leverage difference must be stated because it increases both upside and downside.

What IRR does not tell you

• Whether annual cash deficits are affordable.
• Whether the assumptions are realistic.
• How volatile or uncertain the result may be.
• How much work the investment requires.
• Whether the investment suits your circumstances.

Use IRR alongside annual cash flow, cash-on-cash return, debt balance and sensitivity analysis.