Time-weighted return: the standard for measuring performance independent of cash flows
A portfolio that earns 20% in year one and loses 10% in year two has a different terminal balance for an investor who deposited evenly across the two years than for one who deposited everything up front. Time-weighted return (TWR) strips out those cash flow effects to isolate the strategy's return independent of when the investor put money in or took it out.
What time-weighted return is
Time-weighted return is the convention for measuring a portfolio's or strategy's return independent of the size and timing of contributions and withdrawals. It treats every period equally regardless of how much capital was invested during that period. The result is a single annualised number that describes the strategy's performance—not the investor's experience.
TWR is the basis for the CAGR figure quoted in fund factsheets, the Sharpe ratio computed in performance attribution, and almost every published comparison between strategies. It is also the basis for the Global Investment Performance Standards (GIPS), the industry-standard reporting framework that asset managers worldwide use to publish performance figures comparable across firms.
How it is computed
The mechanics are straightforward. The total period is divided into sub-periods bounded by external cash flows (deposits or withdrawals). Within each sub-period, the return is computed without reference to flows. The sub-period returns are then chain-linked: TWR = (1 + r₁) × (1 + r₂) × … × (1 + rₙ) − 1. Annualising converts the cumulative TWR into a per-year figure: CAGR = (1 + TWR)^(1/years) − 1.
Consider a portfolio worth USD 10,000 at the start of the year. The investor adds USD 5,000 at mid-year. By year-end, the portfolio is worth USD 16,500. The naive return—(16,500 − 15,000) / 15,000 = 10%—is misleading because it credits the strategy for the USD 5,000 contribution. The TWR splits the year at the contribution date: if the portfolio was worth USD 11,000 at mid-year (a 10% sub-period return), and grew from USD 16,000 (post-contribution) to USD 16,500 (a 3.1% sub-period return), the chain-linked TWR is (1.10 × 1.031) − 1 = 13.4%. The strategy delivered 13.4% over the year; the investor's terminal balance is something else.
For frequent or continuous cash flows, the Modified Dietz method approximates TWR using a single weighted-average calculation rather than period-by-period chain-linking—useful when daily cash flows make exact sub-period boundaries impractical.
What the evidence shows
The case for TWR as the standard reporting convention is straightforward: it is the only return measure that lets investors compare two managers without contaminating the comparison with the timing of cash flows. A manager whose fund received heavy inflows just before a drawdown does not appear worse than one whose fund had stable assets through the same drawdown when both are reported on a TWR basis. Without that adjustment, comparisons would be dominated by flow timing rather than by skill or strategy.
The GIPS standards, first published in 1999 and updated periodically, codify TWR as the required reporting convention for managed accounts and pooled funds. The SEC's marketing rule (rule 206(4)-1) similarly requires TWR for net-of-fee performance presented to prospective clients in most contexts. The convention is therefore consistent across regulators and standard-setters globally.
For evaluating a strategy in isolation—comparing 60/40 to a more dynamic alternative, for example—TWR is the right number. The investor's experience may differ from the strategy's TWR depending on when contributions arrived, but the strategy itself is summarised by TWR.
Limitations and trade-offs
TWR's main limitation is precisely its strength: it tells the investor how the strategy performed, not what the investor actually earned. An investor whose contributions arrived just before a drawdown earned materially less than the headline TWR suggests, and an investor whose contributions arrived just before a rally earned more. For investor-specific performance reporting, money-weighted return (the internal rate of return on the actual cash flows) is the relevant measure.
TWR also requires that the sub-period boundaries be drawn at the actual cash flow dates. If sub-period boundaries are drawn approximately—at month-end rather than at the cash flow date, for instance—the resulting figure deviates from the true TWR by an amount that depends on intra-period volatility. The Modified Dietz approximation is acceptable for retail-scale portfolios with infrequent flows; institutional GIPS-compliant reporting typically requires daily-valuation or transaction-level computation.
For very short evaluation windows or portfolios with very large cash flows relative to size, TWR can produce counter-intuitive results. The chain-linking is sensitive to extreme sub-period returns, and a single very small post-contribution sub-period can dominate the calculation.
Time-weighted return in pfolio
pfolio reports time-weighted return as the default performance figure for any asset or portfolio—CAGR and cumulative return are both computed on a time-weighted basis directly from the price series, independent of contributions or withdrawals. The choice of close or adjusted close price as input is configurable via advanced settings. The metrics are visible in pfolio Insights.
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