S&P 500 Split: NDX-Overlap vs SPX-Only

S&P 500 split into Nasdaq-overlap vs everything else · cap-weighted · weekly data · built because this chart doesn't exist anywhere else
Live · Updated 2026-08-07 18:38 UTC
Window
Jul 2025 — Jul 2026
Why does this dashboard exist?
SPY blends 500 stocks together and cap-weighting hides the divergence between tech mega-caps and the rest of the market. This tool surgically splits the S&P 500 into two buckets — stocks that also live in the Nasdaq 100 vs everything else — and tracks each cap-weighted bucket independently. The result: a clean read on whether markets are being driven by a handful of tech giants or by genuine broad participation.
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NDX-Overlap Leading
Rally is narrow. Mega-cap tech carrying the index. Watch for breadth deterioration.
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SPX-Only Leading
Rally is broad. Financials, healthcare, industrials participating. Healthier structure.
NDX-Overlap Bucket A
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77 S&P 500 stocks that are also in the Nasdaq 100. Cap-weighted. Top names: NVDA (12.3%), AAPL (12.0%), GOOGL/GOOG (21%), MSFT (7.3%). This bucket behaves like a concentrated tech portfolio.
+21.3%
77 stocks · cap-weighted
SPX-Only Bucket B
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398 S&P 500 stocks that are not in the Nasdaq 100. Cap-weighted. Top names: BRK-B, LLY, WMT, JPM, V. Financials, healthcare, industrials, energy, utilities. The "rest of America".
+17.8%
398 stocks · cap-weighted
A/B Ratio
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Relative performance of NDX-overlap vs SPX-only, indexed to 100 at the start of the selected window. Above 100: tech mega-caps outperforming. Below 100: broad market leading. This is the core divergence signal.
99.25
Broad market leading
Spread (A – B)
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Return difference between the two buckets over the selected period. Positive = NDX-overlap stocks outperformed. Negative = broad market outperformed. A large negative spread often signals a rotation from tech into value.
-0.9%
period return differential
Data window
52 weeks
weekly bars in window
📊 Indexed Performance (Base = 100)
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Both buckets re-indexed to 100 at the start of the selected window. The gap between cyan (NDX-overlap) and green (SPX-only) shows which bucket is outperforming. SPY (grey dashed) is shown as the blended S&P 500 reference — it sits between the two by construction.
NDX-Overlap (A) — 85 stocks
SPX-Only (B) — 416 stocks
SPY (reference)
⚖️ Ratio: NDX-Overlap / SPX-Only (indexed to 100)
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The ratio of Bucket A's cumulative return vs Bucket B's. When the line is rising, tech mega-caps are taking the lead. When falling, the broad market is catching up or tech is selling off. Watch for sustained trends and reversals — they often signal regime changes.
Above 100 = Nasdaq stocks outperforming · Below 100 = Broad market leading
Current signal: NDX OVERLAP LEADS — Ratio 103.00 The NDX-overlap bucket has outperformed the SPX-only bucket by 3.5pp over the selected period.
📉 12-Week Rolling Spread: NDX-Overlap minus SPX-Only (%pts)
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12-week rolling return of NDX-overlap minus SPX-only. Cyan bars: tech leading over the past 12 weeks. Green bars: broad market leading. Consecutive bars in the same direction = a confirmed regime. A flip in colour is worth watching.
Positive = NDX-overlap leading · Negative = SPX-only leading
📖 How to extract market information
Step 1
Pick your timeframe
Use 1M or 3M for tactical reads. Use 1Y for regime context. Use 5Y/10Y to see the structural dominance of tech vs the rest.
Step 2
Check the ratio (Panel 2)
This is the core signal. Rising = tech driving the market. Falling = broadening rally. A trend that lasts 8+ weeks is a confirmed regime, not noise.
Step 3
Check the spread bars (Panel 3)
Look for a colour flip — when bars switch from cyan to green (or vice versa) for 3+ consecutive weeks, a rotation is likely underway.
Watch for
Ratio extremes
When the 10Y ratio reaches historic highs (above 200), tech concentration is extreme. When it compresses sharply, forced selling or rotation is happening. Both are tradeable signals.
⚠️ Not financial advice. Market-cap-weighted buckets based on Wikipedia S&P 500 constituent list and official Nasdaq-100 composition. SPY included as cap-weighted S&P 500 reference. Updated daily. | ProInvestorClaw — eToro Popular Investor Analytics