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Probability-Weighted Growth Scenarios

Quick definition: Probability-weighted scenario analysis builds three or more DCF models (bull, base, bear) reflecting different growth outcomes, assigns a probability to each, then calculates a weighted fair value that captures both opportunity and downside. This approach is less brittle than point-estimate DCF and better reflects the uncertainty inherent in forecasting growth.

Key Takeaways​

  • Single-point DCF estimates give false precision; scenarios acknowledge that growth outcomes have a range and different probabilities.
  • Bull cases typically assume aggressive market expansion, higher retention, or faster product adoption; bear cases assume competitive pressure, churn acceleration, or market saturation.
  • Probability assignments should reflect historical outcomes for comparable companies, not wishful thinking; base case should be median outcome, not average of bull and bear.
  • Sensitivity tables for WACC and terminal growth rate are valuable within each scenario, not as replacements for multiple scenarios.
  • Compare your probability-weighted valuation to the current stock price; if the market is pricing a heavy bear-case outcome, the risk/reward may be asymmetric.

Why Scenarios Beat Point Estimates​

Growth investing is inherently uncertain. A high-growth SaaS company might accelerate into enterprise, hit market saturation, face a disruptive competitor, or execute flawlessly for a decade. A single DCF with one growth rate, one margin, and one terminal value implies false confidence about an unknowable future.

Scenario analysis acknowledges this uncertainty. Instead of saying "Company A will grow 30% for five years," you model three outcomes:

  • Bull: 40% growth for five years, then 8% terminal growth, margins expand to 35%
  • Base: 25% growth for five years, then 4% terminal growth, margins reach 28%
  • Bear: 10% growth for three years, then 2% terminal growth, margins compress to 18%

Each scenario produces a different fair value. Assigning probabilities (e.g., 25% bull, 50% base, 25% bear) creates a weighted fair value and reveals the probability distribution of outcomes.

This approach is especially powerful for growth stocks, where small changes in growth or margin assumptions produce large valuation swings. A scenario model quantifies that sensitivity and forces you to articulate what would need to go right (bull) or wrong (bear) for the investment thesis to change.

Constructing the Bull Case​

The bull case assumes the company executes at the edge of what's plausible and favorable macro conditions persist.

Growth assumptions: Accelerated adoption in the TAM, successful geographic or product expansion, or new use cases driving incremental revenue. For a data analytics SaaS company, the bull case might assume they penetrate Fortune 500 companies (a large net-new segment) and average contract value (ACV) increases by 30% as customers add more users.

Quantitatively, bull-case growth might be 40–50% for the first three years (vs. current 30%), decelerating to 15–20% by year seven before reaching terminal growth of 5–6%.

Margin assumptions: In a bull case, operating leverage kicks in. The company has already invested in R&D, sales infrastructure, and global operations; incremental revenue is now highly profitable. Bull-case operating margins might be 35–40%, versus a base case of 25–28%. The margin improvement is usually modest (5–10 percentage points from base), not transformational.

Terminal growth: Bull cases often assume terminal growth of 4–5%, a point above GDP growth but still conservative. A company like Figma or Stripe with large remaining TAM might justify 5–6% terminal growth in a bull case, reflecting decades of continued expansion ahead.

WACC and capital allocation: Bull cases sometimes assume the company achieves investment-grade credit quality and the cost of capital declines. They might also assume more aggressive capital return (buybacks, special dividends) once growth slows, increasing shareholder returns.

Probability: What percentage of scenarios result in the bull case? For a well-positioned company with proven execution and a large TAM, 25–35% is reasonable. For earlier-stage or more competitive businesses, 15–20%. For turnarounds or distressed situations, 5–10%.

Constructing the Base Case​

The base case is the median outcome, not the average of bull and bear. It's what a smart analyst would forecast if forced to make a single prediction, adjusting for both execution risk and market dynamics.

Growth assumptions: Base-case growth reflects the company's current trajectory minus some deceleration for competitive intensity, market saturation, or macro headwinds. If a company has grown 35% for the past three years, a base case might assume 25–28% growth for the next five years, decelerating to 8–10% by year seven, then 3–4% terminal growth.

Margin assumptions: Base case margins are below bull-case levels but above bear, reflecting normal operating leverage and some competitive pressure. For a SaaS company with 40% gross margin, base-case operating margin might be 25–28%, acknowledging that increased competition or customer concentration risk may prevent margin expansion to bull-case levels.

Terminal growth: Base-case terminal growth is typically 3–4%, close to long-term GDP growth. It assumes the company is a large, mature competitor in its market but still growing above inflation.

Probability: Base cases are assigned 50–60% probability, reflecting the median outcome and anchoring the weighted valuation. This forces you to take a clear stance on what's most likely, not hedge with equal weighting.

Constructing the Bear Case​

The bear case captures downside scenarios without assuming bankruptcy or total failure. It reflects competitive disruption, market saturation, macro pressure, or execution missteps.

Growth assumptions: Bear-case growth is materially lower than base. If base is 25%, bear might be 10–15% for the first three years, then decelerating to 3–4% and terminal growth of 1–2%. A bear case might also include an assumption that the company loses market share to competitors or fails to expand into new segments.

Margin assumptions: Bear margins reflect price competition, increased customer acquisition costs, or inability to scale operations efficiently. Gross margins might be stable, but operating margins compress due to fixed costs not declining proportionally with revenue deceleration. A bear case might show operating margins at 15–18%, down from 25%+ in base.

Specific triggers: The strongest bear cases articulate what would cause this outcome. Examples: a major competitor launches a lower-cost offering and captures 30% of the market; the company's largest customer (15% of revenue) churns; a recession causes enterprise software spending to drop 20%; product innovation stalls and churn accelerates from 5% to 10% annually.

Probability: Bear cases are assigned 15–25% probability for well-positioned companies, 30–40% for competitive or early-stage businesses. A bear case doesn't need to be probable; it needs to be plausible and has a tail-risk probability.

Probability Assignment​

This is where scenario analysis becomes more art than science. Probabilities must be realistic, not aspirational.

Use historical benchmarks. What percentage of high-growth SaaS companies actually sustain 25%+ growth for five years? Research from analyses of public comps suggests it's roughly 40–50% of companies launched in growth years. The other 50–60% experience competitive pressure, market saturation, or execution issues that slow growth to 15–20% range. Use this distribution to inform your own probability assignments.

Adjust for the specific company's position. If the company has a unique product, strong retention, and a large TAM, tilt probabilities toward bull. If the company operates in a highly competitive market or has execution questions, tilt toward bear.

Sanity-check against current valuation. If the current stock price is $50 and your probability-weighted fair value is $65, the market is pricing in a partial bear case or assuming lower growth than base. If your base case implies $70 and the stock is trading at $50, the risk/reward is attractive.

Building the Three-Scenario DCF​

Here's a numerical example for a $5B revenue SaaS company:

Bull Case (30% probability)

  • Years 1–5 growth: 40%
  • Years 6–10 growth: 20%, then 5%
  • Operating margin year 10: 40%
  • WACC: 8%
  • Implied valuation: $180 billion

Base Case (50% probability)

  • Years 1–5 growth: 25%
  • Years 6–10 growth: 12%, then 4%
  • Operating margin year 10: 28%
  • WACC: 9%
  • Implied valuation: $95 billion

Bear Case (20% probability)

  • Years 1–5 growth: 12%
  • Years 6–10 growth: 5%, then 2%
  • Operating margin year 10: 20%
  • WACC: 10%
  • Implied valuation: $45 billion

Probability-weighted valuation: (0.30 × $180B) + (0.50 × $95B) + (0.20 × $45B) = $54B + $47.5B + $9B = $110.5 billion

This becomes your fair value estimate. If the company has 2 billion shares outstanding, fair value per share is $55.

Sensitivity Within Scenarios​

Within each scenario, you can also build a sensitivity table for WACC and terminal growth rate. This shows how bull-case valuation varies if WACC is 7% vs. 9%, or terminal growth is 4% vs. 6%. But this is a refinement within a scenario, not a replacement for scenarios.

The key insight is that WACC and terminal growth assumptions matter less when you're assigning probabilities to multiple outcomes. A 1% WACC shift might swing bull-case value by 15%, but if bull is only 30% probable, the impact on weighted fair value is modest.

Using Scenarios to Set Position Size and Risk Management​

Scenario analysis also informs position sizing. If you're bullish but have material uncertainty:

  • A base case that matches current valuation might warrant a small position (2–3% of portfolio).
  • A base case that's 30% above current price might warrant a full position (5–7%), with an expectation to hold as the market reprices.
  • A base case that's 60% above current price might warrant a large position but with a stop-loss or hedge if key assumptions break.

Conversely, if your bear case is triggered (growth suddenly decelerates, margin compression appears imminent), you can reassess whether the position is still attractive at a lower valuation.

Next​

Continue to Multiple Expansion vs Compression to understand how valuation multiples expand and contract independently from growth fundamentals, and how to anticipate these shifts.