CSTL vs SPY: Correlation
Castle Biosciences, Inc. (CSTL) and SPDR S&P 500 ETF Trust (SPY) show a weak relationship: their 3-year correlation of weekly returns is 0.18.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are CSTL and SPY?
Across a 3-year window, the weekly returns of CSTL and SPY correlate at 0.18, weak. Lately the two have drifted apart, with the 1-year correlation at -0.04 versus 0.18 over 3 years. Stretching to 5 years gives 0.30, with an annualized covariance of 164.8 %².
Out of 12 assets tracked against CSTL, SPY lands near the bottom at #8. Their recent paths diverged sharply: over the last 12 months CSTL outperformed by 33.2 percentage points (+53.8% for CSTL against +20.6% for SPY). One caveat on sizing: CSTL is 4.4 times as volatile as the other leg, so an equal-dollar split is far from equal-risk.
How is this computed?
Pearson correlation on weekly returns: ρ(A,B) = cov(rA, rB) / (σA · σB), over windows of 52, 156 and 260 weeks. Covariance is annualized (×52) and expressed in %². Full definitions on the methodology page.
CSTL vs SPY: side by side
| CSTL (Castle Biosciences, Inc.) | SPY (SPDR S&P 500 ETF Trust) | |
|---|---|---|
| 1-year return | +53.8% | +20.6% |
| 5-year return | -54.0% | +82.4% |
| Volatility (ann.) | 64.2% | 14.5% |
| Beta vs S&P 500 | 0.79 | 1.00 |
| Max drawdown (3Y) | -57.8% | -18.8% |
| Market cap | $1.0B | – |
| P/E (trailing) | – | – |
| Dividend yield | 0.00% | 1.01% |
| Expense ratio | – | 0.09% |
| Assets under management | – | $795.3B |
| Sector / category | US Listed | ETF · US Large Cap |
SPY is a Large Blend fund from State Street Investment Management: $795.3B under management, 504 holdings, a 0.09% expense ratio, a 1.01% trailing dividend yield.
Year-by-year returns
| Year | CSTL | SPY |
|---|---|---|
| 2022 | -45.1% | -18.2% |
| 2023 | -8.3% | +26.2% |
| 2024 | +23.5% | +24.9% |
| 2025 | +46.0% | +17.7% |
| 2026 | -11.9% | +13.7% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are CSTL and SPY good diversifiers for each other?
Yes. With a correlation of 0.18, CSTL and SPY have moved largely independently, which makes them a genuinely diversifying pair by historical standards.
FAQ
What is the correlation between CSTL and SPY?
Using weekly returns as of 2026-08-27: 0.18 over 3 years, with -0.04 over the last year and 0.30 over 5 years.
Is SPY a good diversifier for CSTL?
Yes. With a correlation of 0.18, CSTL and SPY have moved largely independently, which makes them a genuinely diversifying pair by historical standards.
What does a correlation of 0.18 mean?
On the −1 to +1 scale, 0.18 describes how much the two returns move together: +1 is lockstep, 0 is independence, negative values mean opposite directions. It says nothing about which performed better.
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Related comparisons
Hubs: CSTL correlations · SPY correlations
