Start with the investor’s ledger
Choose the boundary of the account being measured. From the investor’s perspective:
- A contribution to the account is negative: the investor pays money in.
- A withdrawal or distribution received is positive: the investor receives money.
- Remaining account value at the measurement date is a positive terminal amount, as though withdrawn then. If the account is actually fully withdrawn, count that receipt once; do not add the same terminal value again.
Buying a share with cash already inside the account is not an external contribution. Nor is a dividend retained inside it an external withdrawal. These transactions affect holdings and value within the chosen boundary. A distribution paid out to the investor crosses that boundary and enters the ledger.
For signed amounts occurring at times measured in years, the annual-effective MWR solves
Two contributions, one annual rate
Consider a synthetic account in USD. The investor contributes 100 at inception, adds 50 exactly one year later, and receives 176 on full withdrawal exactly two years after inception. There are no other flows, fees or taxes in this example.
| Time from inception | Investor cash flow, USD |
|---|---|
| 0 years | −100 |
| 1 year | −50 |
| 2 years | +176 |
The equation is
The first contribution has two years of exposure; the second has one. The 26 USD cash profit alone does not encode that timing or provide an annual percentage return.
There is also a useful root check. Set . Multiplication by gives
The roots are and . The latter implies and violates the positive-base convention. It is an algebraic root, not a second admissible investment return. More complicated schedules can have multiple admissible IRRs or none; a calculator’s single output does not settle that question.
Why this is not the fund’s time-weighted return
When clients control contributions and withdrawals, TWR is generally the more useful starting point for comparing managers; MWR records the client’s particular investment experience. When the manager controls capital calls or distributions, their timing can itself be part of the investment decision being evaluated. Neither return alone establishes skill or adjusts for risk.
Keep dates and costs visible
Also label the cost basis. Fees deducted inside the account already reduce its value; do not subtract them a second time. Costs paid outside it need appropriate treatment if the intended measure includes them. A quoted MWR should say what fees and taxes are included, alongside its horizon and rate convention.
Sources
- CFA Institute, GIPS Standards Handbook for Firms, November 2020, discussion of Provisions 2.A.28–2.A.29: MWR, IRR and valuation requirements for time-weighted calculations.
- Elton, Gruber, Brown and Goetzmann, Modern Portfolio Theory and Investment Analysis, 9th ed., Wiley, 2014, Chapter 26, “Measures of Return,” pp. 661–662: external flows, linked returns and manager comparison.
- Microsoft, IRR function and XIRR function: regular-period and dated cash-flow conventions.