Every time one company buys another, the accountants get involved before the ink is dry. Purchase accounting (governed by ASC 805 in the US and IFRS 3 internationally) is the set of rules that determines how the acquirer records the deal on its own balance sheet — and it's one of the most commonly tested accounting topics in M&A and private equity interviews.

The Core Idea: Fair Value, Not Book Value

When Company A buys Company B, Company A doesn't simply add Company B's old book values to its own balance sheet. Instead, it has to restate every identifiable asset and liability it acquires to fair value as of the acquisition date. This process is called purchase price allocation (PPA).

In practice, three things almost always happen during a PPA:

  • Asset step-ups. Physical assets like PP&E, and sometimes new intangible assets that never appeared on the target's books at all (customer relationships, technology, trade names), get written up to fair value.
  • A deferred tax liability (DTL). In a typical stock deal, the tax basis of those assets doesn't step up along with the book basis. That book/tax gap creates a new deferred tax liability at close.
  • A deferred revenue haircut. The target's deferred revenue balance — cash already collected from customers for services not yet delivered — gets written down to the fair value of the remaining obligation, which is almost always lower than the amount originally collected.

Whatever the acquirer pays above the fair value of everything it can separately identify becomes goodwill — an intangible asset that sits on the balance sheet indefinitely and is never amortized, only tested for impairment.

Why the Deferred Revenue Haircut Trips People Up

This is the part of purchase accounting that surprises even experienced analysts. If a SaaS company had $10m of deferred revenue on its books before being acquired, the acquirer might only be allowed to record $4m of that as a liability — because accounting standards say the liability should reflect the cost of fulfilling the remaining obligation, not the cash originally collected for it.

The consequence: as that smaller liability is recognized as revenue over the following months, the combined company reports less revenue than the target would have reported on a standalone basis — even though nothing about the underlying business changed. This is a purely mechanical, accounting-driven dip, and it's a classic trap in accretion/dilution and pro forma modeling if you forget to adjust for it. The underlying concept is the same one covered in What Is Deferred Revenue? A Finance Interview Guide, just applied at the moment of an acquisition rather than in the ordinary course of business.

Working Through the Numbers

The mechanics are easiest to see with a worked example. Our case Purchase Accounting After an Acquisition walks through a full deal: a $500m purchase price, a PP&E step-up, a new customer relationships intangible, the resulting deferred tax liability, and the deferred revenue haircut — all the way to a final goodwill figure and the incremental annual depreciation and amortization burden the combined company carries afterward.

If you want to see how goodwill behaves after the deal closes — specifically what happens when the acquired business underperforms and the company has to test for impairment — our case on Goodwill: Creation and Impairment picks up exactly where purchase accounting leaves off.

How the Step-Up Connects to Everyday Depreciation Mechanics

The PP&E step-up in a purchase price allocation isn't a special new concept — it's the same capitalize-and-depreciate mechanic tested in 3-Statement Change: Depreciation Increases by $100, just applied to a revalued asset base rather than a newly purchased one. The combined company simply depreciates the stepped-up asset values going forward, exactly the way it would depreciate any other capitalized cost, which is why the incremental D&A burden from a deal can meaningfully depress reported earnings in the years immediately following an acquisition even though cash flow is far less affected.

Why Interviewers Care

Purchase accounting shows up constantly in M&A, private equity, and even generalist accounting interviews because it tests three things at once: whether you understand fair value versus book value, whether you can trace a deferred tax liability through a deal, and whether you know that goodwill is a plug, not an input. Getting comfortable with the mechanics — ideally by working through a full numerical example rather than just memorizing the definition — is one of the highest-leverage things you can do before a technical interview.

How to Turn This Into a Structured Interview Answer

Understanding purchase accounting conceptually is only half the battle — interviewers usually phrase this as "walk me through purchase price allocation" rather than asking for a definition outright. How to Answer a Purchase Price Allocation Interview Question (Step-by-Step Framework) covers the exact structured approach for turning this concept into a confident spoken answer, including the order interviewers expect each piece — step-ups, DTL, deferred revenue haircut, goodwill plug — to be presented in.

A Numerical Variation to Practice

To make sure the underlying logic is understood rather than memorized from a single deal, consider a smaller $200m acquisition where the target's PP&E is stepped up by $15m, a new $10m customer relationships intangible is recorded, the resulting deferred tax liability is calculated at a 25% rate on the combined step-up ($25m × 0.25 = $6.25m), and the target's $6m of deferred revenue is written down to a $2.5m fair value haircut. If the target's identifiable net assets at fair value (after all these adjustments) come to $150m, goodwill is the plug: $200m purchase price minus $150m of fair-valued net assets equals $50m of goodwill. Running the same waterfall against a different deal size, rather than only reciting one case's numbers, is what separates a candidate who understands the mechanic from one who has memorized a single worked example.

Common Ways Candidates Lose Points on This Question

A few recurring mistakes show up when candidates answer this prompt under interview pressure. Some forget the deferred tax liability entirely, treating the step-up as a costless revaluation instead of recognizing that book and tax basis diverge. Others get the direction of the deferred revenue haircut backwards, assuming the liability gets written up rather than down. Still others describe goodwill as if it were an independently calculated value rather than the plug that makes the balance sheet balance after every other adjustment is made. Avoiding these three slips is what separates a clean answer from a shaky one.

How This Question Escalates at the Associate Level

At the analyst level, interviewers are typically satisfied once a candidate correctly names the three main adjustments — step-ups, DTL, deferred revenue haircut — and explains that goodwill is the plug. At the associate level, the question often extends into modeling judgment — for instance, asking how the incremental D&A from the step-ups flows through the combined income statement and affects accretion/dilution, or asking why the deferred revenue haircut can make an acquisition look artificially dilutive in its first year even if the underlying deal is value-creating. Being ready to move from "here is the mechanical answer" to "here is how this affects pro forma modeling" is what separates a strong associate-level answer from a merely correct analyst-level one.

Industry Patterns Worth Knowing Before the Interview

How large these purchase accounting adjustments are varies significantly by industry. Software and services acquisitions tend to generate large deferred revenue haircuts and a high proportion of the purchase price allocated to goodwill and intangibles, since so much of the target's value sits in customer relationships and technology rather than physical assets. Industrial and manufacturing acquisitions, by contrast, typically involve larger PP&E step-ups relative to goodwill, since more of the target's value sits in tangible, separately identifiable assets. A candidate who can name which industries generate which kind of purchase accounting adjustments demonstrates a more grounded understanding of the topic than one who treats every deal the same way.

Why This Question Is a Favorite Screening Tool

Interviewers return to purchase accounting because it's one of the few topics that simultaneously tests accounting fundamentals, deal mechanics, and modeling judgment in a single question. A candidate who has internalized the underlying waterfall — fair value everything, tax-effect the step-ups, haircut the deferred revenue, plug the rest to goodwill — can handle any deal size or structure, while a candidate who has only memorized one specific worked example will struggle the moment the interviewer changes the numbers. Because this concept sits at the intersection of accounting, tax, and M&A modeling — three areas that show up constantly in finance interviews for deal-focused roles — mastering the underlying logic, rather than any single case, is the highest-leverage way to prepare for this entire question family.

A Pre-Interview Checklist for This Question

Before an interview where this exact topic might come up, it's worth confirming: can you name the three main purchase accounting adjustments — asset step-ups, the resulting deferred tax liability, and the deferred revenue haircut — without hesitating; can you explain why goodwill is a plug rather than an independently determined value; can you explain why the deferred revenue haircut makes reported revenue dip immediately after a deal closes even though nothing about the business changed; and can you connect the step-ups to the incremental D&A the combined company will carry going forward. If any of these feel shaky, revisit the full worked case linked above before attempting this question again.

How This Connects to Goodwill Impairment Down the Road

The goodwill created in a purchase price allocation doesn't just sit quietly on the balance sheet forever — if the acquired business underperforms expectations, that goodwill can later be written down through an impairment charge. Why Doesn't a Goodwill Impairment Increase Cash Flow? The Missing Tax Shield Explained covers exactly what happens when that day comes, including why the impairment typically carries no tax shield — a direct consequence of the fact that the goodwill itself was created without an associated tax basis in the first place. Understanding both ends of the goodwill lifecycle, creation and potential impairment, gives a much more complete picture than studying either one in isolation.

The Takeaway

Purchase accounting is fundamentally a waterfall: restate everything to fair value, tax-effect the differences between book and tax basis, haircut any deferred revenue to its fair value, and let goodwill absorb whatever is left over. Practicing this waterfall against a range of deal sizes and asset mixes, rather than memorizing one case's numbers, is what makes a candidate resilient to however the interviewer happens to phrase the question — and it's the foundation for understanding what happens to that goodwill years later when the deal doesn't work out as planned.