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Spero Therapeutics Inc (SPRO) fair value: what the stock is really worth

As of Sep 23, 2026: fair value of Spero Therapeutics Inc $2.50, price $1.26, upside +98.4%, quality 77 out of 100. Calculated from audited financials with 26 valuation models and 37 quality factors, updated daily.

  1. Fair value above price? Yes
  2. Good quality? Yes
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Healthcare · US · ISIN US84833T1034

ST Spero Therapeutics Inc logo Some data Sep 23, 2026

Spero Therapeutics Inc

SPRO · US

Strongly undervaluedStrong Fair Value upside with high Quality.

✓Fair value $2.50 · Strongly undervalued (+98%)
✓Quality 77/100
!Mixed Growth (revenue 5y +44.9 %/yr)
✓Solidly profitable · 15.7% net margin (TTM)
!Low debt · negative free cash flow
✓Ranks above peers (11/12)
!Moderate moat 61/100
!Evidence only medium, so the estimate is less certain
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What runs behind every stock

26 valuation models 8 families, DCF to NCAV 37 quality factors margins, balance sheet, cashflow, debt 6 AI factors moat, what no ratio measures 2,000+ data points verified, per stock, median

69 individual criteria per stock, every one traceable See the method →

Price vs Fair Value

$19.51 $0.5600 Fair Value $2.50 Jun 2021 Sep 2026

White line = price, green steps = our fair value per fiscal year, dashed = 300-day average. As of Sep 23, 2026.

How to read this chart

60‑month range $0.5600 – $19.51 · fair‑value band $1.88 – $3.13 · the $1.26 price screens below the $2.50 fair value. Green steps = our fair value per fiscal year (point-in-time, no hindsight). Dashed = 300-day average. As of Sep 23, 2026.

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Company profile

Spero Therapeutics, Inc., a clinical-stage biopharmaceutical company, focuses on identifying and developing novel treatments for multi-drug resistant (MDR) bacterial infections and rare diseases in the United States.

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Spero Therapeutics, Inc., a clinical-stage biopharmaceutical company, focuses on identifying and developing novel treatments for multi-drug resistant (MDR) bacterial infections and rare diseases in the United States. The company's product candidates include Tebipenem HBr (tebipenem pivoxil hydrobromide), an oral carbapenem-class antibiotic to treat complicated urinary tract infections, including pyelonephritis for adult patients, which has completed second Phase 3 trial. It has license agreement with Meiji Seika Pharma Co., Ltd. to develop, manufacture, and commercialize tebipenem pivoxil and tebipenem HBr; and Everest Medicines to develop, manufacture, and commercialize SPR206 in Greater China, South Korea, and Southeast Asian countries. Spero Therapeutics, Inc. was incorporated in 2013 and is headquartered in Cambridge, Massachusetts.

Stock analysis

Spero Therapeutics Inc (SPRO) currently trades at $1.26, while our model-based Fair Value estimate is $2.50, implying the stock looks roughly 49.6% undervalued today.

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Valuation

Bull case: the Growth Earnings group reads highest at a median of $6.84 per share, and 7 of the 9 models we run sit above the $1.26 price.

Bear case: the Asset-Based group reads lowest at $0.6800, and 2 of the 9 models stay below the price. Evidence for this calculation is medium.

Scenario range: $1.88 (bear) to $3.13 (bull), the price of $1.26 sits below it. Bear and bull are the same models on cautious and optimistic assumptions, a range, not a price target.

Quality & growth

The Quality Score stands at 77/100 (high quality), in the Healthcare sector.

Mixed Growth: Revenue is growing, but margins or cash flow do not fully confirm the trend.

Spero Therapeutics Inc reported revenue of $59.6M in FY2025 versus $3.1M in FY2021, a compound +109.9%/yr. Reported net income was $8.6M in FY2025.

Key figures

Market cap $73.0M · P/E ratio 9.0 · P/S ratio 1.29 · EPS (TTM) $0.1400 · Net margin 14.4% · Return on equity 19.2% · Return on assets (EBIT) −28.0% · Operating margin 14.1%.

Competitive moat

Our AI-assisted moat analysis scores the competitive advantage at 50 out of 100 (low confidence).

What moves the price

The share trades about 58% below its 52-week high and 14% above its 52-week low, currently below its 200-day average.

For context, the median of 10 Healthcare peers we cover trades at −5% fair-value upside, at 98%, SPRO screens cheaper than that median.

Fair Value models

Bear $1.88 Fair Value $2.50 Bull $3.13
Model ⓘEach model values the company its own way (discounted cash flow, earnings, assets, dividends). The fair value above is their evidence-weighted blend, not the output of a single model. Based on fiscal year 2025 figures (about 9 months old). Earnings retained since then ($0.1028 per share) are deliberately not added. Bear ⓘBear = the cautious scenario: the same model computed with conservative anchors (lower growth, margins and valuation multiples). Together with Bull it frames a plausible valuation range, not a price target.BaseBull ⓘBull = the optimistic scenario: the same model computed with favourable anchors (higher growth, margins and valuation multiples). Together with Bear it frames a plausible valuation range, not a price target. Evidence ⓘEvidence = how well-backed THIS model's estimate is for this stock (0–100): how complete and reliable its input data are, and how well the model fits the company. The final Fair Value is an evidence-weighted blend, so better-evidenced models count more. Green ≥70, amber 50–69, grey below 50.
Highest evidence
Residual Income $0.9000 $1.04 $1.86 66
Growth-Adj P/E $4.79 $6.84 $8.89 65
P/E Multiple $2.43 $3.24 $4.05 63
All 9 models by family
Earnings-Based
Graham-Dodd $1.00 $6.98 $9.80 61
Lynch FV $3.61 $5.15 $6.70 59
PEG = 1.0 $3.61 $5.15 $6.70 55
Multiples
P/E Multiple $2.43 $3.24 $4.05 63
P/S Multiple $1.88 $2.50 $3.13 58
P/B Multiple $1.88 $2.50 $3.13 55
Asset-Based
NCAV (Graham) $0.5100 $0.6800 $1.01 54
Economic Profit
Residual Income $0.9000 $1.04 $1.86 66
Growth Earnings
Growth-Adj P/E $4.79 $6.84 $8.89 65

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Quality Score breakdown

Overall quality 77/100

Of which business quality 72 · Market factors (momentum, volatility) 5

Profitability 71
Margins and returns on capital today
Quality Growth 100
Are margins and returns improving?
Cashflow 33
Earnings quality: real cash, not paper profit
Fin. Strength 75
Balance sheet, leverage, solvency risk
Investment 100
Disciplined investing over empire-building
Low Volatility 12
Calm price path (market factor)
Momentum 0
Price trend over the last 3–12 months (market factor)
52W Momentum 4
Distance to the 52-week high (market factor)
Net Issuance 75
Share count: buybacks or dilution?

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Revenue & earnings trend

Growth Quality ⓘGrowth is valuable only when reinvestment earns attractive returns (Aswath Damodaran): sustainable growth depends on return on capital, reinvestment and efficiency. Basis: total company revenue over the periods shown on the cards (3Y/5Y/all years), not per share, so a merger can show up as a growth jump; per-share earnings growth is in the value-creation card. 59/100
Revenue is growing, but margins or cash flow do not fully confirm the trend.
Revenue growth 1 year
+24.3%
Revenue growth 3 years ⓘMeasures the company's TOTAL revenue from reported annual statements: compound average growth per year (CAGR) from the fiscal year 3, 5 or N years back to the most recent comparable fiscal year. Not per share: buybacks do not change this number, and a merger can appear as a growth jump. Per-share growth (which does include buybacks) is in the value-creation card.
+7.1%
Revenue growth 5 years ⓘMeasures the company's TOTAL revenue from reported annual statements: compound average growth per year (CAGR) from the fiscal year 3, 5 or N years back to the most recent comparable fiscal year. Not per share: buybacks do not change this number, and a merger can appear as a growth jump. Per-share growth (which does include buybacks) is in the value-creation card.
+44.9%
Start year 2020 (pandemic)
Revenue growth 9 years ⓘMeasures the company's TOTAL revenue from reported annual statements: compound average growth per year (CAGR) from the fiscal year 3, 5 or N years back to the most recent comparable fiscal year. Not per share: buybacks do not change this number, and a merger can appear as a growth jump. Per-share growth (which does include buybacks) is in the value-creation card.
+77.8%
What shareholders gained per year (last 3 years) ⓘWhat the business itself delivers per year: earnings growth per share plus the dividend yield. This is what you get IF the market keeps valuing the stock the same way: it contains no assumption about the market changing its mind. Computed per share, so buybacks count and a merger does not pass as growth. For a company that pays no dividend it is pure earnings growth per share. Period: earnings growth per share as CAGR over the last 3 reported fiscal years (annual statements), plus the current dividend yield. The start value is the median of the three years around the start, so a single crisis year (a pandemic or a write-down) does not distort the rate. Basis: adjusted.
−34.3%
Earnings growth per share plus dividend.
Earnings per share, growth per year−34.3%
Dividend (yield on the price)0.0%
Profit margin 2020 to 2025 ⓘOperating margin then vs now, from reported annual statements. A falling margin after a boom year is the classic peak-earnings signal: the growth rate then leans on an inflated base.−848% → 0%

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Peer GroupⓘHow this stock ranks against its industry: the green marker is this stock, the band is the typical 25–75% peer range, and the tick is the median.Biotechnology · 649 stocks

Beats the industry median on 11/12 measures
Overall it ranks above its industry peers.
Valuation
Quality Score 77 · Top 25%
Fair Value upside +98% · Top 25%
Profitability
Return on equity (TTM) 19% · Top 25%
Return on assets 7% · Top 25%
Net margin (TTM) 16% · Above median
Operating margin (TTM) 14% · Above median
Growth and dividend
Revenue growth −96% · Bottom 25%
Balance sheet
Debt / equity 0.00× · Lowest 25%

Valuation Multiplesvs Biotechnology median · lower = cheaper

P/E (TTM) 9.0× · Cheapest 25%
P/B 1.24× · Cheaper than median
P/S (TTM) 1.55× · Cheaper than median
EV/EBITDA 4.6× · Cheapest 25%

Strength profile in five axes (Snowflake)

VALUEFUTUREPASTHEALTHDIVIDEND
This stock
VALUEFUTUREPASTHEALTHDIVIDEND
Sector peers
VALUE (fair-value potential)100 · sector 0
FUTURE (revenue growth)0 · sector 0
PAST (return on equity)77 · sector 0
HEALTH (low debt)100 · sector 97
DIVIDEND (yield)0 · sector 23

Context: sector, industry, market

Values & ESG

Does this company touch areas you may want to avoid? The classification is inferred from sector and industry.

None of the checked exposures detected

Similar stocks

10 more Biotechnology stocks, each showing price versus our Fair Value estimate.

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Vertex Pharmaceuticals Incorporated VRTX $516.34 $567.97 +10%
Regeneron Pharmaceuticals, Inc REGN $801.82 $1,252 +56%
argenx SE ARGX $963.79 $918.60 −5%
Samsung Biologics Co 207940 1,366,000 KRW 1,502,600 KRW +10%
CSL Limited CSL A$179.12 A$197.03 +10%
Alnylam Pharmaceuticals, Inc ALNY $251.65 $218.36 −13%
Royalty Pharma plc RPRX $58.52 $24.22 −59%
BeOne Medicines AG 6160 HK$218.20 HK$169.72 −22%
Celltrion, Inc 068270 177,400 KRW 74,519 KRW −58%
BioNTech SE BNTX $100.87 $63.62 −37%

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Cite: Fair Value Calculator (2026). "Spero Therapeutics Inc Fair Value". https://www.fairvalue-calculator.com/stock/SPRO

Frequently asked questions

Is Spero Therapeutics Inc (SPRO) overvalued or undervalued?
As of Sep 23, 2026, our model estimates a fair value of $2.50 versus a price of $1.26, about +98% upside (undervalued).
What is the fair value of SPRO?
Our model-based fair value for Spero Therapeutics Inc is $2.50 (as of Sep 23, 2026), built from audited fundamentals. The current price: $1.26.
What is the quality score of SPRO?
Spero Therapeutics Inc has a Quality Score of 77/100. It measures business quality (profitability, growth, cash flow, balance-sheet strength, investment discipline, share issuance). Market factors such as price momentum and volatility do not enter the number; they are shown separately in the detail view.
What is the price target for Spero Therapeutics Inc (SPRO)?
Our model-based price target is the fair value of $2.50 (as of Sep 23, 2026) from 9 valuation models. Cautious scenario $1.88, optimistic scenario $3.13. It is a calculation from audited fundamentals, not an analyst target.
What is the Spero Therapeutics Inc stock forecast for 2026?
Our models put fair value at $2.50, about +98% upside versus a price of $1.26 (undervalued). Cautious scenario $1.88, optimistic scenario $3.13. The calculation is refreshed regularly with new filings.
What is the revenue of Spero Therapeutics Inc (SPRO)?
Spero Therapeutics Inc reported trailing-twelve-month revenue of about $47.0M (latest available figure, as of Sep 23, 2026).
What is the intrinsic value of Spero Therapeutics Inc (SPRO)?
Intrinsic value and fair value mean the same thing: what the business is worth on its numbers, independent of the share price. For Spero Therapeutics Inc it is $2.50 per share (as of Sep 23, 2026), against a price of $1.26. It is the blended result of 9 valuation models (cash flow, earnings, asset, dividend).
Is Spero Therapeutics Inc stock overvalued or undervalued in 2026?
As of Sep 23, 2026, SPRO trades below its calculated fair value: price $1.26, fair value $2.50, a gap of about +98% (undervalued). The calculation is refreshed with each new quarterly report, so the verdict can change during the year.
Is fair value the same as the market price of SPRO?
No. The price is what the market pays today ($1.26); the fair value is what the company's own numbers justify ($2.50). For Spero Therapeutics Inc the two are $1.24 per share apart. That gap is exactly why we show both numbers side by side.
How much is Spero Therapeutics Inc worth?
The market values Spero Therapeutics Inc at about $73.0M (market capitalisation, as of Sep 23, 2026). Per share that is $1.26; our models calculate a fair value of $2.50 per share.
What do the bullish and bearish scenarios say about SPRO?
Our models span a range for Spero Therapeutics Inc: cautious scenario $1.88, base $2.50, optimistic $3.13 per share (as of Sep 23, 2026, price $1.26). The range comes from different growth and margin assumptions, not from analyst opinions.
What is the P/E ratio of SPRO?
Spero Therapeutics Inc trades at a price-to-earnings ratio of 9.0 (as of Sep 23, 2026). A P/E on its own says little: it compares the price with ONE year of profit, while our fair value of $2.50 is built from several models across several years. Excluding one-off items of fiscal year 2025 it is 7.9 (reported 8.4). Other multiples: P/B 1.2, P/S 1.6, EV/EBITDA 4.6.
How solid is the balance sheet of Spero Therapeutics Inc (SPRO)?
Balance-sheet figures for Spero Therapeutics Inc (as of Sep 23, 2026): return on equity 19.2%, debt of 0.00 per unit of equity. They feed the Quality Score of 77/100, which measures business quality independently of the share price.
How far is SPRO from its 52-week high?
Spero Therapeutics Inc trades at $1.26, about 58% below its 52-week high of $2.98 and 14% above the low of $1.11 (as of Sep 23, 2026). Distance from the high says nothing about value: that is what the fair value of $2.50 is for.
Which stocks are comparable to Spero Therapeutics Inc?
From the same area (Healthcare) we also value Vertex Pharmaceuticals Incorporated, Regeneron Pharmaceuticals, Inc, argenx SE, Samsung Biologics Co, among others. Each of them has its own fair-value calculation on this site using the same models, so the comparison is like for like.
Is Spero Therapeutics Inc stock attractive at the current price?
The data as of Sep 23, 2026: price $1.26, calculated fair value $2.50 (+98%), Quality Score 77/100, from 9 models. Whether that fits your horizon and risk tolerance is your call. We provide the calculation, not investment advice.
How is the fair value of SPRO calculated?
We run Spero Therapeutics Inc through 9 models from four families: discounted cash flow, earnings models, asset and balance-sheet models, and dividend models. Every model gets the same audited fundamentals; the result is the weighted average of $2.50, with the spread shown as a cautious and an optimistic scenario.
Is it still worth investing in stocks now?
The global stock market currently sits 13.0 % above its aggregate fair value. Spero Therapeutics Inc currently trades 98 % below its own fair value, and the market average says nothing about that. An expensive market is no reason to stay out and no reason to buy everything at once: keep a broad savings plan running, buy single stocks only with money you can do without, and hold part of your money liquid while the market is high. The full picture including sectors is on is it worth investing now.
What is the share price of Spero Therapeutics Inc (SPRO)?
The closing price on Sep 23, 2026 was $1.26. Our model-based fair value is $2.50, about +98% upside (undervalued). We carry closing prices from our data provider, not a live tick.
What should I pay attention to with Spero Therapeutics Inc right now?
The rarer combination: high quality (77/100) AND below fair value. That earns a closer look rather than a quick verdict. The price is below even our cautious bear case ($1.88). The market is more pessimistic than our downside scenario.

Key figures of Spero Therapeutics Inc

How large is the market capitalisation of Spero Therapeutics Inc (SPRO)?
The market capitalisation of Spero Therapeutics Inc is $73.0M. The stock-market value of the whole company: share price times number of shares. It is what the market asks for the entire business today.
What is the P/S ratio of Spero Therapeutics Inc (SPRO)?
The price-to-sales ratio of Spero Therapeutics Inc is 1.29 (P/E × margin). Price to sales: market value relative to yearly revenue. Useful when profit is thin or distorted.
What are the earnings per share of Spero Therapeutics Inc (SPRO)?
Earnings per share at Spero Therapeutics Inc are $0.1400 (price ÷ EPS = P/E 9.0). Earnings per share over the last twelve months: total profit spread across every single share.
What is the net margin of Spero Therapeutics Inc (SPRO)?
The net margin of Spero Therapeutics Inc is 14.4% (fiscal year 2025). How much of every unit of revenue ends up as profit. 10% means 10 cents of profit per dollar of sales.
What is the return on equity of Spero Therapeutics Inc (SPRO)?
The return on equity (ROE) of Spero Therapeutics Inc is 19.2% (last twelve months). Profit relative to shareholders' equity, how efficiently the company works with its owners' money.
What is the EBIT return on assets of Spero Therapeutics Inc (SPRO)?
On an EBIT basis the return on assets of Spero Therapeutics Inc is −28.0% (avg 5y). Operating profit (EBIT) relative to everything the company owns, as a multi-year average. It describes the business model rather than one good or bad year.
What is the operating margin of Spero Therapeutics Inc (SPRO)?
The operating margin of Spero Therapeutics Inc is 14.1% (last twelve months). Profit from the core business (before interest and taxes) relative to revenue.
How fast is revenue growing at Spero Therapeutics Inc (SPRO)?
Revenue at Spero Therapeutics Inc is growing −95.6% versus a year earlier (3y avg +7.1%). How much revenue grew versus a year earlier (YoY). The 3-year average next to it puts the single year in context.
How fast are earnings growing at Spero Therapeutics Inc (SPRO)?
Earnings per share at Spero Therapeutics Inc are growing +75.3% versus a year earlier. How much earnings per share grew versus a year earlier.
How much free cash flow does Spero Therapeutics Inc (SPRO) generate?
The free cash flow of Spero Therapeutics Inc is −$12.6M (fiscal year 2025). The cash truly left after running and investing in the business, this is what pays dividends and buybacks.
How much net cash does Spero Therapeutics Inc (SPRO) hold?
Spero Therapeutics Inc holds more cash than debt, $37.4M net (fiscal year 2025). The company holds more cash than debt, a safety cushion.
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