The Horizon IRR Metric Keeps Being Misused

by Michael Roth

Accurately measuring performance and estimating asset class returns is the most important part of the asset allocation process. The reason it is important is two-fold: (1) return estimates have the biggest impact on your asset allocation model and (2) studies have shown that asset allocation is a critical component of returns.

Considering this, industry trade groups, like the BVCA, and service providers, like Cambridge Associates, continue to inappropriately tout a horizon IRR calculation in comparison to the public market’s 1,3, 5, or 10 year time weighted rate of return.

As I have discussed previously, it is a mistake to think an IRR and a time weighted return are one and the same. Both are annualized rates of return but they deal with cash inflows and outflows in different ways. IRR specifically accounts for the timing and size of cash flows when calculating the returns generated while the time weighted return specifically excludes the impact of cash flows and weights the returns in each time period equally. Each method has their shortcomings and ideal use cases. Take these metrics out of context and they can be misleading.

What difference does a return calculation make?

I used a portfolio of 481 North America and Global buyout funds from Bison’s cash flow dataset to analyze the difference between the horizon IRR and the time weighted return. Both return calculations were performed using quarterly cash flows.