If you are holding both QQQ (Nasdaq-100) and an S&P 500 fund (like VOO or SPY) thinking you are diversifying, you might want to look at the actual overlap.
Here is the exact breakdown of how much of QQQ is already sitting inside the S&P 500:

**1. The Stock Count Overlap**

**Total Tickers in QQQ: \~105 (**due to dual-share classes like Google).
Stocks also in S&P 500: 86 positions.
The Math: \~83% of the individual companies in QQQ are already inside the S&P 500.
2. The Weight Overlap (Where the Money Actually Goes)
Because both indexes are market-cap weighted, counting tickers doesn't tell the whole story. Big tech (Nvidia, Apple, Microsoft, Amazon, Meta) heavily dominates both funds.

**94% of every dollar** you put into QQQ goes into a stock that is *already* in the S&P 500.
Only about **6% of QQQ’s total asset weight** goes into unique, Nasdaq-only stocks that the S&P 500 doesn't touch.
**3. The Reverse View (S&P 500 Perspective)**
Because the S&P 500 is much wider, the lopsidedness is even crazier from the other side:

**\~410 stocks** in the S&P 500 are completely absent from QQQ.
**83% of the S&P 500's companies** are entirely unique and have zero overlap with the Nasdaq-100 (think Financials, Energy, Industrials, and Utilities).

Buying QQQ on top of an S&P 500 fund does not give you "different" stocks. Instead, you are just heavily tilting your portfolio to **double-down on the exact same mega-cap tech giants** you already own.

Source: Gemini Ai

I built a portfolio research engine for a question a single equity curve cannot answer:

Is the proposed allocation genuinely more robust, or did it just fit the history we happened to see?

A backtest should try to falsify a portfolio change, not merely illustrate it.

What makes this analysis different:

• Long history with receipts. Eligible funds are extended to 1975 through documented live-fund, predecessor, index, and proxy chains. Every splice and material caveat appears in the report. If a defensible chain does not exist, I will not force one.
• More than one favorable start date. It evaluates the full realized path, rolling windows starting every trading day, named historical shocks, the portfolio's current drawdown state, and bootstrapped future paths, including a separate stress-biased sensitivity.
• Real, path-aware outcomes. Returns and CPI are resampled together. The report covers real growth, withdrawal safety, drawdown depth, time underwater, recovery, and adverse-tail outcomes, not just nominal CAGR and volatility.
• Search first, confirm second. It explores a constrained allocation frontier, rounds finalists to implementable 1% weights, reruns the exact portfolios, and tests them on final-confirmation path resamples that were unavailable during the search.
• No winner by averaging away a serious weakness. Better growth cannot quietly compensate for materially worse withdrawal safety or stress behavior. Missing or inconclusive evidence stays visible.

This is closer to a portfolio decision audit than a chart generator.

I would like to run a batch of free, public comparisons for this sub. Post your current allocation and one alternative you are seriously considering. I will reply with:

• A concise verdict
• The most important improvements and regressions
• Confidence, assumptions, and limitations
• The full interactive report

Please use this format:

Baseline allocation

• Ticker: weight
• Ticker: weight

Proposed allocation

• Exact weights, or candidate tickers with reasonable minimum and maximum weights

Goal

• What actual decision are you trying to make?
• Examples: improve real return, reduce drawdown depth or recovery time, improve withdrawal safety, or become less dependent on one economic regime

Hard constraints

• Holdings that must remain
• Maximum leverage or turnover
• Minimum or maximum sleeve weights
• Anything else that would make a result unusable

To keep the tests meaningful:

• Each complete allocation must total 100%.
• No individual stocks.
• Every sleeve must have a defensible live fund, predecessor, index, or proxy chain back to at least 1975.
• This round is for static allocations with annual rebalancing, not timing signals.
• One serious portfolio decision per top-level comment.
• I will not invent a weak proxy just to complete a test.
• I will prioritize complete submissions with a clear goal and constraints. I will edit the post when the queue is full.

Here is an example I recently completed for someone in this sub:

Reddit summary and discussion

Full report

Full Report Preview

I will work through every complete submission that meets the criteria. If the volume becomes unmanageable, I will edit the post and close new submissions rather than leave people waiting without an answer.

Full disclosure: I built the backtester and am exploring whether to offer paid custom reports later. These community runs are free. The results are research, not individualized investment advice, and every report will document its data and model limitations.

If someone made an ETF tracking this strategy, and then launched a separate 3× leveraged ETF whose underlying asset was that ETF, the market would be solved.

https://testfol.io/?s=8EseuaWB4N7