My broker told me I was up 12% last year.
The real number, once I accounted for currency conversion losses and the timing of my capital additions, was closer to 7%.
That's not a rounding error. That's a 5-point gap that changes how you evaluate every decision you made that year.
If you invest across multiple brokers, hold assets in different currencies, or move capital in and out of positions throughout the year, the return number your broker shows you is almost certainly wrong. Not maliciously. Just structurally. Broker dashboards are not built to calculate true portfolio performance. They're built to show you activity on their platform.
There's a difference.
Why Broker Return Numbers Are Misleading
Every broker calculates returns differently. And most of them use the simplest possible method: they compare your current value to your starting value and call it a return.
That works fine if you invested a lump sum on January 1st and never touched it.
It breaks immediately the moment you:
- Add capital mid-year
- Withdraw funds at any point
- Hold positions in a different currency than your base
- Pay transaction fees, custody fees, or conversion spreads
- Split your portfolio across multiple platforms
Which is to say: it breaks for almost every real investor.
TWR vs MWR: The Two Numbers You Need to Understand
There are two ways to measure portfolio return properly. Most investors have never heard of either.
Time-Weighted Return (TWR)
TWR eliminates the effect of external cash flows — deposits and withdrawals — so you can evaluate the performance of your investment strategy independently of when you added or removed money.
It answers the question: how well did my portfolio perform, regardless of my timing decisions?
TWR is the standard used by professional fund managers. It's the number that lets you compare your strategy against a benchmark fairly.
Calculating it manually requires breaking your portfolio into sub-periods every time cash flows in or out, computing the return for each sub-period, and chain-linking them multiplicatively. For a portfolio with monthly contributions across four brokers, that's dozens of calculations per year.
Money-Weighted Return (MWR)
MWR — also called IRR at the portfolio level — accounts for the size and timing of your cash flows. It answers a different question: how well did my money actually perform, given when I deployed it?
If you added a large amount right before a market drop, your MWR will be lower than your TWR. If you happened to invest heavily before a rally, it'll be higher. MWR reflects the reality of your specific decisions.
Neither metric is "better." They answer different questions. The problem is that most brokers show you neither — they show you a simplified gain/loss percentage that conflates both and accounts for neither properly.
The Currency Problem Nobody Talks About
If you hold USD-denominated assets and your base currency is EUR, your broker's return figure is almost certainly calculated in USD.
That matters more than most investors realize.
A position up 15% in USD terms might be up only 7% in EUR terms if the dollar weakened during your holding period. Or it might show 20% if the dollar strengthened. The currency movement is not a minor adjustment — in volatile years it can be larger than the underlying asset's return.
My own experience: a 5–10% gap between what the broker showed and what I actually had after converting back to euros. Not because the broker was wrong in their own terms. Because their terms weren't my terms.
A true return calculation has to be done in your base currency. Every position, every dividend, every fee — converted at the rate applicable on the date of the transaction.
No broker does this automatically across multiple platforms. No spreadsheet maintains this accurately over time without constant manual intervention.
The Hidden Costs That Erode Real Returns
Currency conversion fees and spreads are the most underestimated drag on retail investor returns.
On Degiro, currency conversion carries a fee that applies every time you buy or sell a non-EUR asset. It's small per transaction. Across a year of activity, it compounds.
Neither of these shows up in the return figure your broker displays. They're already baked into your prices, invisible unless you calculate them explicitly.
Add custody fees, inactivity fees, and any platform-specific charges, and the gap between headline return and true return widens further.
The math isn't complicated. But doing it manually, across four platforms, in multiple currencies, for every transaction in a year — that's the problem.
What True Return Calculation Looks Like by Hand
Let's make the complexity concrete. Suppose you want to calculate your MWR for the year across your portfolio.
You need:
- The starting value of your portfolio on January 1st
- Every cash inflow (deposits, dividends received) with exact dates
- Every cash outflow (withdrawals, fees paid) with exact dates
- The ending value on December 31st
- All of the above converted to your base currency at the exchange rate on each transaction date
Then you solve for the rate r in this equation:
Ending Value = Starting Value × (1+r)^t
+ CF₁ × (1+r)^(t-t₁)
+ CF₂ × (1+r)^(t-t₂)
+ ... CFₙ × (1+r)^(t-tₙ)
Where each CF is a cash flow and each t is the fraction of the year remaining at the time of that cash flow.
This requires numerical iteration to solve — there's no closed-form algebraic answer. In Excel it's the XIRR function. By hand it's trial and error.
Now multiply that by four brokers, twelve months of dividends, currency conversions at different rates on different dates, and exchange-specific fees.
This is not a calculation problem you solve with a better spreadsheet. It's an integration problem — you need software that connects to your accounts, ingests transaction data automatically, applies the correct exchange rates, and computes the result continuously.
What Snowball Shows You Instead
Snowball Analytics does this automatically.
Every position across your connected brokers is tracked in your base currency. Returns are calculated using proper methodology — accounting for cash flow timing, currency movements, and fees. The number you see is your actual return, not your broker's simplified approximation.
The difference isn't cosmetic. For an investor with a multi-currency, multi-broker portfolio, the gap between a broker's headline number and a properly calculated return can be 5–10 percentage points. That's the difference between thinking your strategy is working and knowing whether it actually is.
Why This Matters for Every Decision You Make
Return calculation isn't academic. It drives every allocation decision you make.
If you think a strategy is returning 12% when it's actually returning 7%, you'll keep deploying capital into it. You'll benchmark it against alternatives incorrectly. You'll attribute performance to skill that was actually currency tailwind — or miss underperformance that was hidden by currency movement.
Conversely, a strategy that looks like 6% in your broker app might actually be 11% once you account for dividend reinvestment timing and a favorable exchange rate. That position deserves more capital, not a review.
The numbers your broker shows you are not wrong. They're just incomplete. And in investing, incomplete information and wrong information produce the same outcome.
The Benchmark Question
Once you have a true return number, the next question is: compared to what?
A 9% return sounds good. Against the S&P 500 returning 15% in the same period, it's underperformance. Against a bond portfolio returning 4%, it's strong outperformance. Against a passive ETF with lower risk and zero time cost, it might not justify the complexity.
You can't answer this question with a broker's simplified return figure. You need TWR — the methodology that strips out your cash flow timing and gives you a clean strategy-level number comparable to any benchmark.
That's the number that tells you whether your active decisions are adding value, or whether you'd be better off in a simple index fund and spending those 10 hours a month on something else.
Looking for technical content for your company? I can help — LinkedIn · kevinmenesesgonzalez@gmail.com
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