Stock fact sheet · data as of
Castle Biosciences, Inc. (CSTL): fair value, margin of safety and Wheel Score
Healthcare · Medical - Diagnostics & Research · United States · Speculative / Distressed
Is CSTL undervalued?
Castle Biosciences, Inc. (CSTL) closed at 33.80 on 16 Oct 2026, 622% above the GLS average fair value of 4.68. 1 of the 1 models that produced a number value the shares below the current price. A gap this wide usually means the market is paying for growth or a story the trailing numbers do not show yet; the models work from filed results, not forecasts, so they are conservative by design.
Only 1 of the nine models produced a value (10 Cap); the others need a dividend, positive free cash flow or positive book value the company does not have yet, so the average rests on a narrow base.
The nightly engine files CSTL under Speculative / Distressed - negative earnings or a Piotroski score of 3 or less - which caps its Wheel Score at 45 and keeps it out of the Sunday Scan.
Nine valuation models for CSTL
Each model turns the latest filed numbers into a value per share; the GLS fair value is the simple average of the ones that produce a positive number. The last two rows are shown for reference and never enter the average. The Quote page lets you switch any model off and add your own margin of safety.
| Model | Value | vs price | What it measures |
|---|---|---|---|
| DCF | - | - | Present value of the projected free cash flows, discounted at the cost of capital; no value tonight |
| Graham Number | - | - | The most a defensive investor pays for the earnings and book value per share; no value tonight |
| Graham Growth | - | - | Graham's growth formula: EPS × (8.5 + 2 × growth), adjusted for bond yields; no value tonight |
| Lynch | - | - | EPS × the earnings growth rate (PEG of 1), growth capped at 25%; no value tonight |
| GLS Growth | - | - | EPS compounded ten years at the blended growth rate, discounted back at 15% a year; no value tonight |
| 10 Cap | 4.68 | -86% | Owner's earnings (operating cash flow less maintenance capex) capitalised at 10% |
| Payback Time | - | - | Eight years of compounded free cash flow: the price at which the business pays for itself; no value tonight |
| DDM | - | - | Dividend discount model: next year's dividend ÷ (10% − 3% growth); needs a dividend; no value tonight |
| EPV | - | - | Earnings power value: current EPS capitalised at 9% with no growth; no value tonight |
| Zombie (liquidation) | 8.30 | -75% | Current assets less all liabilities, per share: the balance-sheet floor. Not in the average |
| Wall St target | 39.00 | +15% | Analysts' average 12-month price target. Not in the average |
Quality and financial health
Financial health is weak: CSTL passes 3 of the nine Piotroski tests. Our screens drop the stock at the health rule; a low score is often the reason a stock looks cheap on the valuation models. The GLS Moat score is low at 2.7 out of 10, which says the ten-year record of revenue, earnings, margins and returns on capital has been inconsistent - growth and shocks rather than steady compounding.
Returns on capital are thin or negative - ROIC -4.8%, ROE -5.1%, ROA -4.2% - with debt at 0.08 times equity and negative free cash flow.
Castle Biosciences, Inc. pays no dividend, so the DDM model does not apply and a covered-call holder earns only the premium and any price gain. Revenue comes mainly from Dermatologic 100% (quarter Q2 FY2026).
Institutional ownership scores 10/10, insider activity 1/10 and Congressional trading 5/10 on the GLS smart-money scales; the last recorded insider buy was on 21 Sep 2026.
| Piotroski F-score | 3 / 9 | ROIC | -4.8% |
|---|---|---|---|
| GLS Moat | 2.7 / 10 | ROE | -5.1% |
| Debt / equity | 0.08 | ROA | -4.2% |
| Free-cash-flow yield | -0.0% | Payout ratio | 0% |
| Institutions | 10 / 10 | Insiders · Congress | 1 · 5 / 10 |
Wheel Score 38: Weak
CSTL scores 38 out of 100 on the Wheel Score, in the Weak band (under 50). Value 0/25, Health 7/20, Moat 4/15, Premium 16/20, Stability 12/20. The score is not a judgement on the company; it says the price, quality and premium do not line up for selling puts on it today.
Implied volatility is 77% on the near-the-money contracts 20-60 days out - above the 60% ceiling of the sweet spot. Premiums are large, but the Wheel Score tapers the Premium points (16 of 20) because volatility this high usually comes with a reason. Chain open interest is thin - 477 contracts across every expiry - so fills at a fair price are not guaranteed; a 30-45-day put may not exist at a usable strike.
Volume runs at 382k shares a day on a market cap of $1.0B, with a beta of 0.94; the Stability part of the Wheel Score gives that 12 of 20.
| Part | Points | From | |
|---|---|---|---|
| Value | 0 / 25 | -622% margin of safety | |
| Health | 7 / 20 | Piotroski 3/9 | |
| Moat | 4 / 15 | moat 2.7/10 | |
| Premium | 16 / 20 | implied volatility 77% | |
| Stability | 12 / 20 | 382k shares/day, $1.0B cap, beta 0.94 |
The Wheel Score ranks ~7,400 US stocks for selling cash-secured puts and covered calls; it is updated nightly and is not a recommendation. The walkthrough lesson shows how the score fits into a trade, start to finish.
Upcoming events
The next earnings report is due on 2 Nov 2026 (after the close), 17 days away; a 30-45-day put sold today would expire after it, which is worth weighing against the premium.
Earnings, dividend, IPO, split and economic calendars for the whole market, filterable to your watchlists.
Similar stocks in Medical - Diagnostics & Research
The 12 companies below are the closest to Castle Biosciences, Inc. by market cap within the Medical - Diagnostics & Research industry, each with its own fact sheet; the Compare page puts up to eight of them side by side.
| Stock | Close | Fair value | MoS | Wheel | Mkt cap |
|---|---|---|---|---|---|
| OPK OPKO Health, Inc. | 1.61 | 0.1839 | -776% | 40Weak | $1.2B |
| PSNL Personalis, Inc. | 15.90 | - | - | 45Weak | $1.7B |
| FLGT Fulgent Genetics, Inc. | 21.34 | 4.31 | -395% | 41Weak | $587M |
| WGS GeneDx Holdings Corp. | 68.61 | - | - | 43Weak | $2.0B |
| NEO NeoGenomics, Inc. | 17.25 | - | - | 45Weak | $2.2B |
| MYGN Myriad Genetics, Inc. | 4.35 | - | - | 45Weak | $416M |
| CDNA CareDx, Inc | 66.68 | 58.58 | -14% | 54Fair | $3.4B |
| VCYT Veracyte, Inc. | 43.51 | 40.63 | -7% | 58Fair | $3.5B |
| BLLN BillionToOne, Inc. | 102.73 | 191.05 | +46% | 81Prime | $4.8B |
| SHC Sotera Health Company | 17.73 | 10.67 | -66% | 58Fair | $5.1B |
| XGN Exagen Inc. | 8.42 | - | - | 43Weak | $204M |
| BDSX Biodesix, Inc. | 24.71 | - | - | 30No options | $201M |
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Start free See the Sunday ScanQuestions about CSTL
Is CSTL undervalued right now?
No: at 33.80 the stock trades 622% above the GLS average fair value of 4.68 (data as of 16 Oct 2026), well beyond what trailing earnings, cash flow and book value support.
What is the Wheel Score of CSTL and what does it mean?
CSTL scores 38 out of 100 (Weak). The Wheel Score blends the margin of safety (25 points), Piotroski health (20), the GLS moat (15), the option premium on offer (20) and trading stability (20) into one number that ranks stocks for the wheel strategy - selling cash-secured puts, then covered calls if assigned. 80 and above is Prime, 65-79 Good, 50-64 Fair, under 50 Weak.
What is the GLS fair value for CSTL?
4.68 per share as of 16 Oct 2026 - the simple average of the 1 valuation models (out of nine: DCF, Graham Number, Graham Growth, Lynch, GLS Growth, 10 Cap, Payback Time, DDM and EPV) that produced a positive value. The models run every night on the latest filings; the Quote page lets you switch any of them off and add a margin of safety of your own.
When does Castle Biosciences, Inc. report earnings next?
The next earnings report is due on 2 Nov 2026 (after the close), 17 days from the data date of 16 Oct 2026. The Calendars page lists every upcoming report with its time of day.
Does CSTL have listed options, and how liquid are they?
Yes. The nightly snapshot found 114 listed contracts with 477 open interest across all expiries and implied volatility of 77% on the near-the-money contracts. The Options scanner lists the cash-secured put and covered call set-ups with premium and annualised yield worked out.