Beyond Simple Percentage Gains
Most investors focus on the wrong number when evaluating their investment performance. They either take their broker’s number (which is usually the simple average), or they use the more complex Return on Investment (ROI) calculation. But even ROI is not enough to calculate your true return. You will need to use a financial calculator or a spreadsheet function like Excel's Internal Rate of Return (IRR) to get your true dollar-weighted rate of return.
Does this sound like more work than is justified? It isn’t. Being under the illusion that you are earning a high rate of return when your true return is sub-par often leads to overconfidence, which is a performance killer.
Most investors look at their portfolio's total return percentage and assume that's their actual investment performance. But this approach ignores a crucial reality: money flows in and out of portfolios at different times, and timing matters enormously.
The Problem with Simple Returns
When you see that your portfolio gained 15% last year, that percentage doesn't tell you how well you performed as an investor. It tells you how the investments performed, but not how your money performed. These are fundamentally different things.
If you had invested a lump sum at the beginning of the year and held it unchanged, you would know your true return because it would be the same as your investment return. However, if you made deposits or withdrawals during the year, including your company’s matching contributions, the numbers would be different. To find your true return, you need to consider what actually happened to the dollars you invested, and when you invested them, along with deposits and withdrawals.
Understanding Time-Weighted vs. Money-Weighted Returns
Time-weighted returns measure how the investments themselves performed, assuming you invested everything at the beginning and held until the end. This is what mutual funds report. But the timing of your purchases, sales, deposits and withdrawals has a very high impact on your easy-to-find simple return.
Money-weighted returns (also called dollar-weighted returns) measure how your actual money performed, accounting for when you added or withdrew funds. This is what matters for your personal wealth building. Having an accurate picture of how you’re progressing towards your money goals is paramount. You will start out on the right path and avoid overconfidence or its opposite – an inferiority complex about how skilled you really are at getting the return you need.
A Real-World Example: Sarah's Investment Journey
Let's follow Sarah, a 35-year-old marketing manager, through one year of investing to see how complex calculating true returns can be.
Sarah's Portfolio Activity
Starting Portfolio (January 1): $50,000
March 15: Sarah receives a $5,000 bonus and invests it immediately
•Portfolio value before addition: $48,000 (market down 4%)
•After $5,000 addition: $53,000
June 30: Sarah withdraws $8,000 for home renovations
•Portfolio value before withdrawal: $58,000 (good recovery)
•After $8,000 withdrawal: $50,000
September 1: Sarah inherits $15,000 and invests it
•Portfolio value before addition: $52,000
•After $15,000 addition: $67,000
December 31: Final portfolio value: $75,000
The Misleading Simple Calculation
A naive calculation might show: ($75,000 - $50,000) ÷ $50,000 = 50% return But this ignores the fact that Sarah added $20,000 and withdrew $8,000, for a net addition of $12,000. A more accurate simple calculation would be: ($75,000 - $50,000 - $12,000) ÷ $50,000 = 26% return But even this is wrong because it doesn't account for the timing of deposits and withdrawals.
The Correct Calculation: Internal Rate of Return (IRR)
To find Sarah's true money-weighted return, we need to calculate the IRR, which accounts for the timing of all cash flows:
•January 1: -$50,000 (initial investment)
•March 15: -$5,000 (additional investment)
•June 30: +$8,000 (withdrawal)
•September 1: -$15,000 (additional investment)
•December 31: +$75,000 (final value)
Using financial calculators or spreadsheet functions,
Sarah's actual IRR is approximately 8.2%.This means Sarah's money earned 8.2% annually, despite the portfolio showing much higher simple returns.
Factors That Influence True Returns
Timing of Cash Flows
Dollar-Cost Averaging Benefits: Regular investments during market volatility can improve returns by buying more shares when prices are low.
Market Timing Risks: Large investments right before market drops significantly hurt returns, while investments before rallies help.
Dividend Treatment
Reinvestment Timing: Dividends reinvested immediately compound differently than dividends received and invested later.
Account Type Impact
401(k) Matching: Employer matches provide immediate returns (often 50-100%) that should be factored into performance calculations.
Tax-Deferred Growth: Traditional IRAs and 401(k)s grow tax-free, but withdrawals are taxed as ordinary income.
Tax-Free Growth: Roth accounts provide tax-free growth and withdrawals, effectively increasing real returns.
Best Practices for Tracking True Returns
Use Portfolio Tracking Software
Tools like Microsoft Excel can calculate money-weighted returns automatically. Many brokerages now provide these calculations in their reporting.
Separate Performance from Behavior
Track both your investment selection performance (time-weighted) and your investment timing performance (money-weighted). This helps identify whether poor returns come from bad investments or bad timing.
Consider After-Tax Returns
For taxable accounts, track after-tax returns to understand your true wealth accumulation rate. A 10% pre-tax return might only be 7% after taxes.
Account for Opportunity Costs
Money withdrawn from investments has an opportunity cost. Sarah's $8,000 withdrawal in June cost her potential gains on that money for the rest of the year.
Regular Performance Reviews
Calculate your IRR quarterly or annually to understand trends in your investment timing and decision-making. This is how you can begin to earn better returns in exchange for a small calculation task once per quarter or year.
The Bottom Line
Your true investment return is not what the market gave you – it's what you actually earned on your money after accounting for when you invested, when you withdrew, fees, taxes, and opportunity costs. This number is almost always different from simple portfolio return percentages.
Understanding this difference helps you make better decisions about when to invest, how much to invest, and whether your investment timing is helping or hurting your long-term wealth building goals.
The most successful investors focus not just on picking good investments, but on consistently investing money when they have it, minimizing fees and taxes, and avoiding the temptation to time the market based on emotions or short-term events.
Download the IRR spreadsheet (Excel). It has all the formulas preloaded for you. Just email me at erik@zeninvestor.org or reply to this message.