Why Simple Return Misleads Active Traders

You added $5,000 to your account in March. You pulled $2,000 out in June to cover a bill. You topped up again in September before a run of good trades. Now your broker shows a single percentage next to your balance, and you have no idea whether that number reflects your skill or just the accident of when your money happened to be sitting in the account.

That single percentage is almost always a simple return, and for an active trader who moves cash in and out, it is one of the most misleading numbers on your screen. It can make a mediocre year look strong. It can make a genuinely good stretch of trading look flat. And because it hides the timing of your own cash flows, it tells you almost nothing about the one thing you actually control.

This post explains why simple return breaks down, what it quietly does to your P&L, and which two metrics measure performance honestly instead.

TL;DR

• Simple return divides total gain by net contributions, so it weights every deposit and withdrawal equally regardless of when it happened.
• A large late deposit can crush your reported return even when your trades were fine. A late withdrawal can inflate it.
• Time-weighted return (TWR) strips out your cash-flow timing and measures how your positions performed.
• Money-weighted return (MWR), also called internal rate of return, keeps that timing in and measures how you did as a capital allocator.
• Use TWR to judge your strategy, MWR to judge your decisions, and never rely on simple return to compare two periods.

What "simple return" actually calculates

Simple return is the number most brokers and spreadsheets show by default. The formula is exactly what it sounds like:

Simple return = (Ending value - Net contributions) / Net contributions

Net contributions here means everything you paid in, minus everything you took out. If you deposited $10,000 in total across the year, withdrew $2,000, and finished with a balance of $12,000, your net contributions are $8,000 and your gain is $4,000, for a simple return of 50%.

The problem is buried in that formula. It treats a dollar you deposited on January 2 exactly the same as a dollar you deposited on December 20. One dollar had a full year to work. The other had eleven days. Simple return cannot tell them apart, so it assigns the same weight to both. As Wealthfront's guide to measuring returns puts it, simple return "weights all deposits and withdrawals equally dating back to whenever you opened the account," which is why "a large, late addition of cash can massively reduce the return of an account or mask losses in that account" (Wealthfront).

For a buy-and-hold investor who funds an account once and leaves it alone, this rarely matters. For an active trader who adds capital after a good month, sizes up before a setup, or sweeps profits out to pay taxes, it matters constantly.

Why a late deposit wrecks the number

Walk through a concrete case. Suppose you start the year with $10,000 and trade it well, growing it to $13,000 by November. That is genuinely a 30% return on the money that was actually at risk.

Then in early December you deposit another $20,000, because you want to scale up. The market chops sideways for the rest of the month, and you finish the year at $33,200. Your total gain is $3,200 on $30,000 of net contributions.

Simple return now reads about 10.7%.

Nothing about your trading got worse. The $20,000 you added late simply had almost no time to earn anything, but simple return divides your very real $3,000 of gains across the full $30,000 as if all of it had been working since January. Your skill did not change. Your reported number fell by nearly two-thirds because of a deposit that had nothing to do with how you traded.

The reverse distortion is just as sneaky. Pull cash out right before a strong run, and simple return flatters you, crediting the whole gain against a smaller contribution base. The number moves for reasons that have nothing to do with the quality of your decisions.

add $20k in December →

The late deposit never had time to earn, but simple return spreads your gains across all of it.

The distortion runs both directions, and it can flip a loss into a "gain"

The clearest published illustration of how badly this can go comes from a single-stock example in Sharesight's return methodology guide. An investor makes three trades in one stock:

• December 2015: buys 1,000 shares at $1.00, spending $1,000.
• December 2016: buys 1,000 more shares at $2.00, spending $2,000.
• December 2017: sells all 2,000 shares at $1.25.

The investor ends up with a real, cash-in-pocket loss of $500. But the two proper return methods disagree sharply on what happened. The money-weighted return is -12.77% per year, because it accounts for the fact that the investor put more money in right at the $2.00 peak. The time-weighted return is +11.80% per year, because the share itself rose from $1.00 to $1.25 over the period, and TWR measures only that underlying move (Sharesight).

Two honest numbers, pointing in opposite directions, from the same trades. One tells you the stock went up. The other tells you your timing of adding capital lost you money. Simple return would smear these together into a single figure that answers neither question and misleads on both.

The two methods that measure performance honestly

The fix is to stop asking one number to do two jobs. Portfolio measurement splits into two well-defined methods, and each answers a different question.

Time-weighted return (TWR) removes the effect of your deposits and withdrawals entirely. It slices your history into sub-periods between each cash flow, calculates the return within each slice, then links those slices together by compounding. Because every cash flow starts a fresh slice, the size and timing of your deposits stop mattering. What is left is the pure performance of the positions you held. This is why TWR is the standard for judging how assets were managed, and why it is required under the CFA Institute's Global Investment Performance Standards (GIPS) for comparing investment managers, on the logic that a time-weighted return "best reflects the firm's ability to manage the assets."

Money-weighted return (MWR), also called the internal rate of return, does the opposite. It keeps your cash-flow timing fully in the calculation and finds the single rate that makes the present value of all your deposits, withdrawals, and ending balance line up. Because it weights each period by how much money was actually invested then, MWR rewards you for putting more capital to work before good stretches and penalizes you for piling in before bad ones. In one worked example, an investor who added money right as growth accelerated saw a money-weighted return of roughly 35%, well above the underlying investment's own pace, precisely because the timing of the deposit was good (AnalystPrep).

Here is the split in one picture.

Which one should you actually watch?

You want both, because they answer questions you both care about.

Track TWR when you are asking whether your trading approach works. Because it ignores your deposits and withdrawals, it lets you compare this quarter to last quarter, or your account to a benchmark like the S&P 500, without the comparison being polluted by the fact that you happened to fund the account differently in each period. If you are trying to answer "is my edge real," TWR is the clean measure. It pairs naturally with the risk-adjusted view you get from a Sharpe ratio, which asks whether the return was worth the volatility you took on to get it.

Track MWR when you are asking whether your capital-allocation decisions were smart. Adding size before a good run and trimming before a bad one is a real skill, and MWR is the only one of these three numbers that gives you credit or blame for it. This is the difference between the two methods in one sentence, and it is worth learning cold before you go deeper into the mechanics in time-weighted vs. money-weighted return.

What you should stop doing is treating simple return as either of these. It is neither a clean measure of your strategy nor an honest measure of your timing. It is a blend that shifts with every deposit, which is exactly why it is a poor basis for comparing periods or asking whether you are improving. Once you know your TWR, you also have an honest input for the bigger question of what counts as a good annual return for traders, rather than a number that flatters or punishes you based on cash-flow accidents.

How to get these numbers without doing the math by hand

The formulas are not hard, but computing TWR and MWR by hand across a year of deposits, withdrawals, and dozens of trades is tedious and error-prone. The practical answer is to let a portfolio tracker do it.

Any tool worth using should value your account immediately before and after each cash flow, so it can slice your history correctly for TWR and solve the internal rate of return for MWR. TradeReveal computes a net-asset-value-based time-weighted return from your own positions and cash flows rather than showing a broker's stale simple-return snapshot, which is the whole reason the number on your dashboard should move with your trading and not with your transfers. If you are still tracking performance in a spreadsheet, the manual version of this is what tends to break first, because it is easy to forget to mark the account value on a deposit day.

The point is not which tool you use. The point is that once you stop looking at simple return, the story your P&L tells you gets a lot more truthful.

Frequently Asked Questions

Is simple return ever the right number to look at?

Yes, in one narrow case. If you funded your account once, never added or withdrew a cent, and never plan to, then simple return, TWR, and MWR all converge on the same answer. The distortion only appears when cash moves in or out. The more active your funding, the more misleading simple return becomes.

What is the difference between time-weighted and money-weighted return in one sentence?

Time-weighted return measures how your investments performed regardless of when you added money, and money-weighted return measures how you performed as an allocator, including whether your deposits and withdrawals were well timed.

Why do professional standards require time-weighted return?

Because managers do not control when clients add or pull money, time-weighted return isolates the part of performance the manager actually influences. The CFA Institute's GIPS standards require it for that reason, so that returns are comparable across firms of different sizes (CFA Institute). Note that the 2020 edition of GIPS does permit money-weighted return under defined conditions, so the two are complements, not rivals.

Can money-weighted and time-weighted return disagree by a lot?

They can point in opposite directions. In the Sharesight single-stock example, the same trades produced a time-weighted return of +11.80% per year and a money-weighted return of -12.77% per year, even though the investor actually lost money overall (Sharesight). The gap is the timing of the investor's own cash flows.

Does deposit timing really change my reported return that much?

It can change it dramatically. A late deposit spreads your existing gains across a larger contribution base without giving that new money any time to earn, which pulls simple return down hard. A withdrawal before a good run does the reverse and inflates it. Neither swing reflects a change in how you traded.

Final Thoughts

The number your broker shows next to your balance is answering a question you probably are not asking. Simple return blends your trading skill with the accidental timing of your deposits and withdrawals, and the more you move cash around, the less it tells you about either.

Separate the two questions and the fog clears. Use time-weighted return to ask whether your strategy has an edge, on equal footing across periods and against a benchmark. Use money-weighted return to ask whether your capital-allocation timing helped or hurt. Keep simple return where it belongs, which is the default label on a dashboard that has not been told you are an active trader. Once you measure the right way, every other performance question you ask, from risk-adjusted return to your target annual number, rests on an honest foundation.

Sources

• Wealthfront: 4 Ways to Measure Your Investment Return
• Sharesight: Time-weighted vs. money-weighted rates of return
• AnalystPrep: Money-Weighted vs Time-Weighted Rates of Return (CFA Level 1)
• CFA Institute: Overview of the Global Investment Performance Standards (GIPS)

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Happy Trading,

The TradeReveal Team