How to Calculate Time-Weighted Returns on Your Investment Portfolio

Open your brokerage app and it shows you a number. Maybe it says +12% or +£4,300. That number feels like it answers the question "how are my investments doing?" but it usually doesn't. Not properly.

The problem is that most brokerage platforms show you a simple gain or loss: the difference between what you put in and what the portfolio is worth today. That calculation ignores when you added money. If you invested £5,000 in January, the market dropped 20%, and you panicked and added another £20,000 in March right before a recovery, your simple return will look great. But your investments didn't perform great. You just happened to put a lot of money in at the right time.

Time-weighted return (TWR) exists to separate those two things: how well your investments performed versus how well you timed your cash flows. It's the standard used by fund managers, required by the CFA Institute's Global Investment Performance Standards (GIPS), and the only way to do a fair comparison between your portfolio and a benchmark like the S&P 500 or FTSE 100.

This post walks through what time-weighted return actually measures, how the calculation works, where it falls short, and when you should use it versus the alternative.

What time-weighted return measures

Time-weighted return measures the compound growth rate of one unit of money invested in a portfolio over a given period. The key word is "one unit." It asks: if you had put £1 into this portfolio at the start and never added or removed anything, what would that £1 be worth at the end?

By removing the effect of deposits and withdrawals, TWR isolates the performance of the investment strategy itself. It doesn't care that you added £10,000 in March or withdrew £3,000 in August. It only cares about what the holdings did between those events.

This is why fund managers use it. A fund manager has no control over when clients deposit or redeem money. Measuring their performance based on client timing would be unfair. TWR measures only what the manager can control: the investment decisions.

How the calculation works

The idea is straightforward even if the maths can get tedious. You break the total period into sub-periods, with each sub-period ending whenever a cash flow happens (a deposit or withdrawal). For each sub-period, you calculate a holding period return (HPR). Then you chain those returns together by multiplying them.

The holding period return for each sub-period is: HPR = (End Value - Begin Value) / Begin Value. The "Begin Value" for each sub-period includes any cash flow that happened at the start of that period.

The overall TWR is then: (1 + HPR1) x (1 + HPR2) x (1 + HPR3) x ... - 1

A worked example

Say you start the year with £10,000 in a portfolio. By the end of June, the portfolio has dropped to £9,000. That's a -10% return for the first half. On 1 July you deposit another £6,000, bringing the portfolio to £15,000. By 31 December, the portfolio has grown to £16,500.

Sub-period 1 (Jan-Jun): HPR = (£9,000 - £10,000) / £10,000 = -10%

Sub-period 2 (Jul-Dec): The starting value is £15,000 (£9,000 + £6,000 deposit). HPR = (£16,500 - £15,000) / £15,000 = +10%

TWR = (1 + (-0.10)) x (1 + 0.10) - 1 = 0.90 x 1.10 - 1 = -1%

The time-weighted return for the year is -1%. Your portfolio lost value on a pure investment performance basis, even though you ended the year with £16,500 from a total investment of £16,000. The reason is that most of your money (the £6,000 deposit) arrived after the downturn and benefited from the recovery, but that was timing luck, not investment skill. TWR strips that out.

Compare this with a simple return: (£16,500 - £16,000) / £16,000 = +3.1%. That +3.1% tells you your total pot grew, which is true and useful, but it doesn't tell you whether the underlying investments performed well.

Why it matters for benchmark comparison

The most common reason to care about TWR is benchmark comparison. If the FTSE All-Share returned 8% this year, did your portfolio beat it or not? You can only answer that question if you compare like with like. The FTSE return is effectively a time-weighted return (it assumes £1 invested at the start, no additions or withdrawals). If you compare your simple return against the FTSE, you're comparing two different things.

This is especially relevant for investors who contribute monthly via a salary. If you invest £500 every month into a global equity fund, your simple return will differ from the fund's published return because of when each £500 went in. TWR puts you on the same basis as the fund, so the comparison is fair.

It's also how the CFA Institute's Global Investment Performance Standards (GIPS) require investment firms to report performance. When a fund says it returned 12% last year, that's a time-weighted return. If you want to know whether your portfolio did better or worse than that fund, you need your TWR, not your simple return.

The practical problem: you need portfolio valuations at every cash flow

The calculation is conceptually simple but practically annoying. Every time you make a deposit or withdrawal, you need to know the exact value of the portfolio at that moment. Not the day before, not the day after. At that point.

For a single fund this is straightforward because the fund has a daily NAV (net asset value). For a personal portfolio with multiple holdings across different platforms, it's harder. You'd need to look up the price of every holding on every date you made a contribution or withdrawal, calculate the total portfolio value at that point, and use that as the boundary between sub-periods.

If you contribute monthly, that's 12 sub-periods per year, each needing a full portfolio valuation. If you contribute weekly, that's 52. Do this in a spreadsheet for a portfolio with 15 holdings and three years of history and you'll understand why most people don't bother. The concept is simple. The bookkeeping is not.

Money-weighted return: the alternative

Money-weighted return (MWR), also known as the internal rate of return (IRR), answers a different question: what was the actual annualised return on the money I invested, given when I put it in and when I took it out?

Going back to the earlier example: you invested £10,000 at the start, added £6,000 in July, and ended with £16,500 in December. MWR would calculate the single discount rate that makes the present value of your cash flows equal to the ending value. In this case, because most of your money (the £6,000) was only invested for six months during the recovery, MWR would show a higher return than TWR.

MWR is sensitive to timing. If you added money right before a rally, MWR will be higher than TWR. If you added money right before a crash, MWR will be lower. This is the point: MWR reflects your experience as an investor, including the consequences of your timing decisions.

When to use which

There's a lot of debate about which metric is "better," but the answer is that they measure different things and you probably want both.

Use TWR when: You want to evaluate how your investment choices performed. Did your mix of funds and stocks beat the market? Should you switch to a simpler index strategy? TWR answers these questions because it removes the noise of cash flow timing. It's also the right metric for comparing your portfolio against a benchmark or another investor's portfolio.

Use MWR when: You want to know how much money you actually made. "I put in £50,000 over three years, and my actual annualised return accounting for the timing of every deposit was 7.2%." That's MWR. It's your personal result, and it's what matters for financial planning and retirement projections.

A useful way to think about it: if your TWR is higher than your MWR, your investments did well but your timing was poor (you added money at bad times or withdrew at good times). If your MWR is higher than your TWR, your timing was good, whether by skill or luck.

What about dividends?

Dividends complicate things slightly. If a fund distributes dividends (rather than reinvesting them), the distribution is effectively a cash outflow from the portfolio. Accumulation fund units reinvest dividends automatically, so there's no cash flow to account for. Distribution units pay dividends out, and those need to be treated as withdrawals in the TWR calculation.

When comparing your portfolio's TWR against a benchmark, make sure the benchmark return includes dividends (a "total return" index) rather than just price appreciation. The FTSE 100 price index and the FTSE 100 total return index can differ by 3-4 percentage points per year because of dividends. Using the wrong one will make your comparison meaningless.

Common misconceptions

"TWR shows the real return." It shows the investment return, not your return. If you put most of your money in during a downturn and benefited from the recovery, your actual experience (MWR) was better than the TWR suggests. TWR is not more "real" than MWR. It measures something different.

"My brokerage shows TWR." Many don't. Some show simple return (total gain divided by total invested). Some show a modified version. Check what your platform actually calculates before treating the number as a true TWR.

"TWR is always better for individual investors." The opposite is often argued. As an individual investor, you control your cash flows. When you add or withdraw money is your decision, and the financial consequences of that timing are yours. MWR captures those consequences. Some financial planners argue that MWR is the more relevant metric for personal portfolio evaluation because it reflects your actual wealth creation, not a theoretical one-unit-invested scenario.

A note on approximations

True TWR requires a portfolio valuation at every cash flow date. In practice, many tools use approximations. The most common is the Modified Dietz method, which estimates the portfolio value at cash flow dates by assuming growth was linear within each sub-period. This is close enough for most purposes and avoids the need to look up historical prices on every deposit date.

The approximation gets less accurate when returns are volatile within a sub-period. If the market swings wildly during a month and you make a deposit mid-month, the linear assumption can introduce meaningful error. Daily valuation solves this but requires price data for every holding on every day, which is why it's mostly practical only with software.

Annualising returns

Once you have a TWR for a given period, you often want to express it as an annualised figure so you can compare it to other returns quoted on a per-year basis. If your TWR over 3 years is 25%, the annualised figure is not 25% / 3 = 8.3%. It's (1.25)^(1/3) - 1 = 7.7%. The difference matters because of compounding. Dividing by the number of years only works for simple interest, which isn't how investments grow.

Be careful annualising returns for periods shorter than a year. A 5% return in 3 months annualises to about 21.6%, which sounds impressive but is misleading. A short strong period extrapolated to a year implies that performance will continue at the same pace, which is rarely the case. Most professionals avoid annualising anything under 12 months.

What to do with all this

If you're investing through a single platform that shows a percentage return, check whether it's TWR or simple return. If it's simple return and you've been making regular contributions, it's almost certainly overstating or understating how well the investments themselves have done. The larger and more frequent your contributions relative to your starting balance, the bigger the distortion.

If you invest across multiple platforms and want a single performance number for your whole portfolio, a spreadsheet can do it but it's painful to maintain. You need to record every cash flow with its date, value your entire portfolio at each cash flow date, and chain the sub-period returns. Miss one deposit or get one valuation wrong and the result is off.

Endute calculates both TWR and MWR for your portfolio automatically. It tracks every security transaction, looks up historical prices, handles multi-currency conversion, and computes the sub-period returns without you needing to maintain anything manually. You can compare your portfolio against benchmark indices directly, with both numbers on the same time-weighted basis so the comparison is fair.

Whether you use a tool or a spreadsheet or just check your platform's reported return, the important thing is to understand which question the number is answering. "How did my investments do?" and "How much money did I make?" are different questions with different answers. Knowing which one you're looking at is the first step to making better investment decisions.