What Is a PWERM Valuation? Definition, How It Works and Examples

PWERM is one of the methods in a practice guide from the American Institute of Certified Public Accountants (AICPA). The guide is called Valuation of Privately-Held-Company Equity Securities Issued as Compensation. Accountants and appraisers use it to value private-company stock issued as pay. The 2025 working draft of its update calls PWERM the scenario-based method. It notes that the method “may also be referred to as the probability-weighted expected return method (PWERM).” The steps are the same under either name.

1. 1.0
   Choose the outcomesWith management, the appraiser lists the realistic exits: an IPO, a merger or sale, a dissolution, or staying private until a later exit.
2. 2.0
   Value the company in eachEstimate the equity value at the date of each exit, as a single figure or a range. The range must include both high and low outcomes.
3. 3.0
   Run the waterfallSplit each exit value among the share classes according to their rights. This order of payment is called the waterfall. Where preferred does better by taking its liquidation preference, it takes it. Where converting to common pays more, it converts.
4. 4.0
   Weight by probabilityGive each outcome a probability. Then adjust the set until the model reproduces the price of the latest round or of recent secondary trades. This check is called calibration.
5. 5.0
   Discount to todayBring each class’s expected payout back to the valuation date at a rate that reflects its risk. The rate can differ by class.
6. 6.0
   Divide by sharesPresent value per class ÷ shares in that class = value per share.
7. 7.0
   Adjust for marketabilityConsider a discount for lack of marketability, because a private share cannot be sold whenever its holder wants.

Step three is where the cap table, the record of who owns which shares, matters. A liquidation preference pays preferred holders first in a weak exit. That can leave common with little or nothing. In a strong exit, preferred converts and both classes are paid alike. PWERM captures this by valuing each scenario separately. A single averaged forecast would hide it.

A company has 6 million common shares and 4 million preferred shares. Investors bought the preferred in the last round at $15 each. That gives them a $60M liquidation preference: 1×, non-participating and convertible one for one. In plain terms, they either get their $60M back first or convert to common, whichever pays more. The appraiser models three exits two years out.

Two lines do the explaining. First, the preferred value of $14.88 lands close to the $15 investors paid. That is the calibration the guide asks for. If it did not match, the appraiser would revise the probabilities or values. Second, before any discount, common is worth about 82% of preferred: $12.16 against $14.88. In two of the three exits, the preference takes cash that common would otherwise share. The DLOM, the discount for lack of marketability, then takes it to $9.73.

PWERM (scenario-based)

A few named exits, each with a value, a date and a probability. Most practical when a liquidity event, such as an IPO or a sale, is close and the outcomes can be named.

Option pricing method (OPM)

Starts from today’s equity value and treats each share class as a call option on it, a claim that pays only above a set value. It models a continuous range of outcomes with no named scenarios. Often used for earlier-stage companies with no visible exit.

Hybrid method

PWERM’s scenarios, with an OPM used inside one or more of them. A typical setup is a named IPO scenario plus an OPM for “the IPO slips and the exit is unknown.”

Current value method

Allocates value as if the company were sold today. It fits only if an exit is imminent and there is little doubt about value or timing.

The choice follows the company’s stage. Two years from an IPO, the scenarios can be named, so PWERM or a hybrid fits. Five years from any exit, the appraiser would have to invent the scenarios, so an OPM is usually easier to defend.

A company that grants stock options needs the fair market value of its common stock. The strike price must not be below that value, so the options stay outside Section 409A, the US tax rule on deferred pay. The regulation does not name methods. It requires “the reasonable application of a reasonable valuation method” and lists the factors. These include recent arm’s-length transactions, meaning sales between unrelated parties, and discounts for lack of marketability. A PWERM, a hybrid or an OPM can each meet that standard. How the appraisal itself is ordered and used is covered in 409A valuation.

The same numbers feed the company’s accounts. Under US GAAP, the US accounting rules, option grants are recorded as an expense at fair value. That is the purpose of the AICPA guide, and it is why auditors and appraisers work from one model. The 2025 draft adds that secondary trades in a company’s stock are now common enough to deserve more weight in calibration than in 2013.

As an IPO approaches, PWERM tends to take over. The IPO becomes a scenario with a date and a value range. The start-up presumption in the 409A regulation, a safe valuation route for young private companies, also stops applying within 180 days of an expected offering.

Common Mistakes When Reading a PWERM

• Treating the IPO price as the valueThe IPO is one scenario. Its payout is weighted by its probability and discounted.
• Ignoring the preference stackCommon gets nothing in a low exit when preferences exceed the proceeds. That is why common is worth less than preferred.
• A model that does not calibrateIf the preferred value does not reproduce the last round’s price, the assumptions are off.
• Too-cheerful downsideA dissolution that returns most of preferred’s money, or arrives early, overstates preferred and understates common.
• Forgetting the DLOMThe discounted payout is the value of a share that can be sold freely. A private share cannot be.

PWERM

Probability-weighted expected return method: share value from named exit scenarios, weighted and discounted.

Option pricing method (OPM)

Values each share class as an option on the company’s equity, over a continuous range of outcomes.

Hybrid method

Named scenarios, with an OPM inside one or more of them.

Waterfall

The order in which exit proceeds are paid out to each share class.

Calibration

Setting the model’s assumptions so that it reproduces the price of a real transaction in the company’s stock.

Liquidation preference

Preferred holders’ right to be paid first at an exit, up to a set amount.

DLOM

Discount for lack of marketability: the cut in value for a share that cannot be sold quickly.

Start-up presumption

A 409A rule that presumes a young private company’s written valuation reasonable. It is unavailable within 180 days of an expected IPO.

409A valuation

The appraisal of common stock that sets the minimum strike price of employee options.

Standards and rules were checked against the primary text on October 2, 2026. The worked example is illustrative. The 409A rules are United States federal tax rules.