S&P 500 or QQQ: which benchmark is honest for your portfolio?

Benchmark choice is where self-deception starts. Pick an index your portfolio can easily beat and every dashboard glows green while you quietly underperform your real alternative.

This is not a small technicality. The entire value of benchmarking, the discipline argued for in the real cost of never benchmarking, depends on the mirror being honest. Hold a portfolio of AI and semiconductor names, measure it against a broad, staid index, and you will spend years congratulating yourself for returns that any cheap tech tracker would have delivered without your help. The dashboard is green. The self-assessment is fiction.

What each one is

The S&P 500 is 500 large US companies, weighted by size, the default claim on "the market", even though it's US-only. QQQ tracks the Nasdaq-100: the hundred biggest Nasdaq non-financials, which in practice means concentrated mega-tech. Same handful of giants dominate both, but QQQ doubles down: more concentration, higher highs (2023–2024), harder falls (2022).

Both are market-cap weighted, meaning each company's share of the index matches its share of the group's total market value. The practical consequence: the biggest companies dominate, and since the biggest US companies are currently technology firms, both indexes lean tech. The difference is degree. The S&P 500 dilutes its tech giants with hundreds of banks, insurers, oil majors, retailers, railroads, and drugmakers. The Nasdaq-100 excludes financials by rule and skips most of the rest by circumstance, so the same giants sit in a far smaller boat and each one rocks it harder.

Neither index, note, is "the market." Both are US-only, and both are large-cap only. For a European investor holding a world tracker like the ones in every default portfolio, the honest mirror may be neither of these, more on that below.

Two different personalities

Because of that construction, the two indexes behave differently in ways a benchmark user should understand. The S&P 500 is the steadier ride: broader sector spread, more of its return coming from unglamorous compounders, dividends contributing a meaningful slice. QQQ is the same trade with the volume turned up: when growth and technology lead the market it tends to run ahead, and when rates rise or the mood sours on growth it tends to fall further, 2022 and the 2023–2024 rebound being the recent exhibit.

This matters for benchmarking because a gap against QQQ means something different from the same gap against the S&P 500. Trailing the S&P by three points in a year suggests your selections lagged the broad market. Trailing QQQ by three points in a year when tech ripped may just mean you weren't 100% concentrated in mega-caps, which is not obviously a sin. The benchmark isn't only a scoreboard; it's a statement about what risk you signed up for.

The honest rule

Benchmark against what you would actually buy instead. That's the whole rule.

If you quit stock-picking tomorrow, would the money go into a world ETF or S&P 500 tracker? Then that's your benchmark. Holding mostly semiconductor stocks, AI names, quantum ETFs? If you'd otherwise buy QQQ, compare to QQQ, beating the S&P 500 while trailing QQQ means your tech bets underperformed dumb tech beta, which is exactly the kind of thing worth knowing.

Beating a benchmark you'd never buy is a party trick. Trailing the one you would buy is the leak worth finding.

A worked example of flattering yourself

Round numbers. Your tech-heavy portfolio returns 18% in a year. A ghost portfolio with your identical deposits in an S&P 500 tracker would have made 12%; the same deposits in QQQ would have made 25%.

Against the S&P 500 you're a hero: six points of outperformance. Against QQQ you're seven points behind the no-effort version of your own strategy. On a €40,000 average balance, that seven-point shortfall is €2,800 in a single year, earned the hard way, through research, conviction, and trading, relative to clicking "buy" once on a tech tracker. Both comparisons use the same portfolio and the same year. Only one of them describes the decision you actually face, because if you stopped picking tech stocks you wouldn't buy a broad index, you'd buy the tech index. The flattering benchmark isn't wrong arithmetically. It's answering a question nobody asked.

Check against both

In practice the two-line view answers questions a single benchmark can't. Ahead of the S&P but behind QQQ in a tech-heavy portfolio? Your sector call was right and your stock selection within it wasn't. Ahead of both? Genuine edge, verify with a longer window. Behind both? At least it's unambiguous.

The two lines also decompose your result into layers: how much came from being in the market at all, how much from tilting toward tech, and how much from your specific names. That's the same information a professional attribution report contains, extracted from nothing more than two ghost portfolios and your own transaction history.

Give the verdict time

One caution before you act on any of this: benchmark gaps are noisy over short windows. A quarter in which you trail QQQ by four points, or lead the S&P by five, is weather, not climate. Concentrated portfolios in particular will swing around any index, in both directions, for reasons that have nothing to do with skill. A single earnings surprise in one of your larger holdings can manufacture a quarter of apparent genius or incompetence all by itself.

The gaps worth acting on are the persistent ones: the portfolio that trails its honest benchmark over three to five years, across a rally and a drawdown, is delivering a verdict rather than a mood. This is also why switching benchmarks after a bad stretch is the cardinal sin of self-measurement. Pick the index that matches what you'd actually buy instead, write the choice down, and keep the same yardstick through the years when it flatters you and the years when it doesn't. A ruler that changes length whenever the measurement disappoints isn't measuring anything.

Keeping the comparison honest

Whichever index you pick, three bookkeeping rules keep the mirror clean. Use the total-return version, dividends reinvested, since your portfolio keeps its dividends; the price-only chart understates the index and flatters you. Replay your own cash flows into the index rather than comparing against its calendar-year number, because your money didn't arrive on January 1, the method walked through in how to benchmark properly. And convert at the daily exchange rate on each transaction date if you invest across currencies, a euro investor's US returns include the dollar's wanderings, and so must the benchmark's; the mechanics are covered in multi-currency portfolio tracking.

Skip any one of the three and the comparison drifts, always, somehow, in the direction that makes you look better. Bookkeeping errors have a curious political bias that way.

One glance, two mirrors

BullBenchmark simulates your exact deposits into the S&P 500 and QQQ simultaneously, toggle either line on the chart. Two honest mirrors, one glance.

And if your honest alternative is really a world index, the two lines still earn their keep: the S&P 500 approximates the large-cap core most world trackers are dominated by, and QQQ shows what pure growth exposure did. The point was never to find the one perfect index. It's to stop grading your own homework against a curve you drew yourself.

The first week of BullBenchmark is free, no card, upload the export you just downloaded and see where you stand.

Related: How to benchmark properly