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    Why GAAP Conversion Belongs in M&A Due Diligence

    August 28, 2026

    A cross-border acquisition does not require a full GAAP conversion before signing, but the buyer should know whether one is coming and how large it will be. A desktop GAAP review during due diligence identifies where the material accounting differences are, how much historical information will be needed and what the conversion will require after close.

    Key takeaways

    • A full GAAP conversion is not needed before signing, but the buyer should know whether one is coming and how large it is.
    • A desktop review during diligence covers two to three years of local GAAP financial statements, the policies likely to differ under US GAAP and a high-level estimate of the differences.
    • If the acquirer is an SEC registrant, Rule 3-05 can require one or two years of audited target financial statements, so historical periods matter before closing.
    • A quality of earnings report does not show whether the target’s financial statements comply with the parent’s accounting framework.
    • Decide who owns the conversion during diligence; leaving that question until after close is a diligence finding in itself.

    When the work is left until after closing, the problems usually surface when someone asks how the European subsidiary is going to report under US GAAP. The subsidiary has historically reported under German HGB, FRS 102, Dutch GAAP or another local framework. The US parent now needs numbers it can consolidate, the auditors want historical support, and the finance team is working all of this out while also dealing with the rest of the post-acquisition integration.

    What goes wrong when GAAP conversion is left until after close

    When accounting conversion is left entirely to the post-close integration, I tend to see the same three issues.

    The accounting bases do not match

    The US parent needs to consolidate the European subsidiary under US GAAP, the subsidiary reports under local GAAP, and the differences are rarely limited to presentation. Leases may be accounted for differently. Revenue recognition policies may not align. Development costs might be capitalized locally but treated differently under US GAAP. Goodwill, deferred taxes, provisions and other areas can also create differences.

    The finance team is then not simply mapping a chart of accounts. It is rebuilding historical financial information under a different accounting framework. I set out the conversion steps for one common framework in how to convert FRS 102 to US GAAP.

    The opening balance sheet is more complicated than expected

    The deal may have been evaluated using financial statements prepared under the target’s existing accounting framework. Once the acquisition closes, the accounting requirements change. Local GAAP differences, purchase accounting adjustments, fair value considerations, deferred revenue, leases and intangible assets can all affect the opening balance sheet.

    None of these issues necessarily changes the economics of the deal, but they can change the accounting, sometimes significantly. That is an unwelcome surprise if nobody scoped the work before closing.

    Historical periods suddenly matter

    This is one of the largest sources of post-close work. Depending on the transaction and the reporting requirements of the combined company, the acquirer may need historical financial information prepared or reconciled under US GAAP, which can mean going back through multiple years of accounting records.

    If the acquirer is an SEC registrant, Rule 3-05 of Regulation S-X (as amended in 2020) sets the requirement. A significant acquired business needs one year of audited financial statements when significance exceeds 20% but not 40%, and two years when it exceeds 40%, measured under the investment, asset and income tests. A foreign target may present those financial statements under IFRS as issued by the IASB without reconciliation, or under its local GAAP with a reconciliation to US GAAP where significance exceeds 30%, audited under US GAAS or PCAOB standards. They are due on Form 8-K within 71 calendar days after the deadline for the initial Item 2.01 report, which is four business days after closing.

    Doing this work after close is possible. Doing it after close while the finance team is also integrating systems, reporting packages, controls, people and processes is much harder.

    A desktop GAAP review, not a full conversion, during due diligence

    I am not suggesting that every cross-border transaction needs a complete GAAP conversion before the acquisition closes. A full conversion can involve a detailed GAAP differences matrix, technical accounting memos, adjustment calculations, historical trial balance recasts, supporting schedules and audit support. That is a project in its own right.

    During diligence, what you usually need is a desktop review. The goal is to understand where the problems are likely to be before you inherit them. That review might include:

    • Reviewing two to three years of local GAAP financial statements and the chart of accounts
    • Identifying accounting policies that may differ materially under US GAAP
    • Focusing on areas such as leases, revenue recognition, deferred taxes, R&D capitalization and goodwill
    • Estimating the potential magnitude of the differences at a high level
    • Identifying issues that may require a formal technical accounting memo or specialist
    • Determining what a full conversion is likely to involve after close

    The fee for a desktop review depends on the number of entities, frameworks and periods in scope. For a starting estimate, use the GAAP conversion cost calculator. For fees from real engagements, see GAAP conversion cost examples.

    You are not trying to solve every accounting issue during diligence. You are trying to understand the scope of the problem. That gives the deal team much better information for planning the integration, setting timelines, budgeting resources and deciding what needs to be addressed in the transaction documents.

    Put accounting integration on the due diligence checklist

    Legal and financial due diligence are standard. GAAP conversion often falls between the two. The quality of earnings report may tell you what the company’s EBITDA looks like, but it does not necessarily tell you what needs to happen to make the company’s financial statements comply with the accounting framework its new parent uses. That is a different question.

    If you are the CFO, finance director or controller involved in a cross-border deal, ask the deal team or the acquirer this early:

    “What accounting framework will this business need to report under after close, and are its financials already prepared on that basis?”

    If the answer to the second part is no, a conversion project is coming. The only open point is whether you identify it before or after the deal closes.

    Five GAAP conversion questions to answer before signing

    You do not need every adjustment calculated, but I would want answers to these five questions.

    1. Where are the material GAAP differences?

    The answer should be specific to the target. For many European businesses, leases, revenue recognition, deferred taxes, development costs and goodwill are good places to start. A SaaS business, a biotech company, a manufacturer and a professional services firm will not have the same conversion issues.

    2. How much historical information will be required?

    The requirement may be an opening balance sheet only, one comparative year or multiple historical periods. It also matters whether the financial statements will ultimately support an audit, investor reporting, a financing or an SEC filing. The answer can change the size of the conversion project completely.

    3. Are there technical accounting issues in the numbers?

    Some differences are mechanical. Others are not. Complex revenue arrangements, contingent consideration, in-process R&D, stock-based compensation, business combinations or internally developed software may require formal technical accounting analysis. I would rather identify those areas during diligence than discover them when the auditors start asking questions.

    4. What will the full conversion require after close?

    Establish the expected scope, the number of entities involved, the documentation required, who has the underlying data, how much support the existing finance team can realistically provide, and the likely timeline and cost. You do not need a perfect project plan before signing, but you do need enough information to avoid treating the conversion as an unexpected post-close problem. For groups with several subsidiaries, I cover sequencing in how to manage GAAP conversions for multiple subsidiaries across Europe.

    5. Who is going to do the work?

    This one gets overlooked. Someone needs to own the conversion: the target’s finance team, the parent company’s accounting team, a technical accounting advisor or a combination. The external auditor is often suggested, but if the group will be audited under SEC independence rules, the audit firm cannot prepare the financial statements it audits (Regulation S-X Rule 2-01(c)(4)). If the answer is “we will work that out after close,” I would consider that a diligence finding in itself.

    What a full GAAP conversion costs

    The cost depends on the complexity of the business, the number of entities and accounting frameworks involved, the historical periods required, and the level of technical documentation and audit support. A single-entity conversion is a very different project from converting a multi-entity European group across several local GAAP frameworks. I explain what drives the cost, with examples of actual projects, in how much a GAAP conversion costs and how I price it.

    During diligence, the aim is not to know the final fee to the dollar. It is to know whether you are looking at a contained conversion or a significant post-close accounting project, and to make sure that work is reflected in the integration plan and budget before the deal closes.

    Scope the GAAP conversion before the deal closes

    A cross-border acquisition does not mean completing a GAAP conversion during due diligence, but it does mean understanding whether one is coming. Once the transaction closes, the accounting work does not disappear. It becomes part of the integration, with less time to plan for it.

    If you are acquiring a European business that will need to report under US GAAP after close, book a strategy call to identify the accounting differences and scope the conversion before you sign.