Methodology

OPM vs Backsolve vs PWERM: Which Equity Allocation Method Is Right?

FairValueX Team · 11 min read

The Three Methods at a Glance

Once you've determined your company's total enterprise value (using DCF, market comps, or other approaches), you need to allocate that value to common shares. This is where OPM, Backsolve, and PWERM come in. They answer the question: "Given total enterprise value of $X, what is each share class worth?"

Option Pricing Model (OPM) — The Workhorse

The OPM treats each share class as a call option on the company's total equity value, with breakpoints defined by the liquidation preferences in your cap table. It uses a Black-Scholes-like framework to value each "tranche" of the capital structure.

When to Use OPM

• ✓ Company is early-to-mid stage (Seed through Series B)
• ✓ No near-term liquidity event expected (18+ months)
• ✓ Multiple share classes with different liquidation preferences
• ✓ You want a widely accepted, defensible method that auditors are comfortable with

Key Inputs & Judgment Areas

• Total equity value: From your enterprise valuation (DCF, comps, or both)
• Volatility: Estimated from comparable public companies — typically 50-80% for VC-backed startups
• Time to liquidity event: Estimated years until exit (IPO or M&A) — typically 2-7 years
• Risk-free rate: U.S. Treasury rate matching the time to liquidity
• Breakpoints: Determined by your cap table's liquidation waterfall

OPM Strengths & Weaknesses

Backsolve — The Market-Anchored Method

Backsolve works in reverse: given a known transaction price (e.g., the price per preferred share in your most recent funding round), it derives the implied total equity value using the OPM framework, then allocates value to common shares.

When to Use Backsolve

• ✓ Recent arm's-length transaction within the last 6-12 months
• ✓ Transaction was with a sophisticated investor (VC, PE) at market terms
• ✓ No material change in the business since the transaction
• ✓ You want to calibrate to market evidence rather than rely solely on your own enterprise valuation

Why Auditors Like Backsolve

Backsolve is anchored to an observable market transaction — the price a willing buyer (investor) actually paid. This makes it less subjective than a standalone DCF or pure OPM, and auditors have clear evidence to reference. However, auditors will scrutinize:

• Whether the transaction was truly arm's-length
• Whether material events have occurred since the transaction
• Whether the terms of the round (ratchets, participating preferred) are properly modeled

PWERM — The Scenario Method

PWERM models multiple discrete exit scenarios (e.g., IPO at $500M, M&A at $200M, stay private, dissolution) and assigns probability weights to each. The common share value is the probability-weighted average across all scenarios.

When to Use PWERM

• ✓ Company is late stage with a likely near-term liquidity event
• ✓ Specific exit scenarios are identifiable and quantifiable
• ✓ The board or management has explicit plans for exit timelines
• ✓ OPM would understate value by ignoring the upside from an imminent IPO or M&A

The PWERM Audit Challenge

PWERM involves the most judgment of any equity allocation method. Your auditor will challenge:

• Scenario selection: Why these scenarios and not others?
• Exit values: How were the exit valuations for each scenario determined?
• Probability weights: Why 40% IPO and 30% M&A instead of 30/40? What evidence supports these weights?
• Timing assumptions: When does each scenario occur, and how did you discount to present value?

This is exactly why professional judgment documentation matters. At FairValueX, our binder includes a complete professional judgment documentation that documents the rationale for every probability weight, every scenario value, and every key assumption — with evidence references. When your auditor asks "why 40% IPO probability?", they find their answer in the binder without a phone call.

The Hybrid Approach: When Methods Converge

In many engagements, the best practice is to use multiple methods and reconcile them. This is what the AICPA Valuation of Portfolio Company Investments Practice Aid recommends.

Common combinations:

FairValueX's structured methodology platform supports all three methods simultaneously, enabling multi-method reconciliation in the same engagement. This produces a more defensible conclusion and directly addresses auditor expectations for methodology triangulation.

Decision Framework