Financial due diligence (FDD): What to review and key red flags

Financial due diligence (FDD) is a detailed review of a company’s financial performance, risks, and underlying records before an acquisition, investment, or other transaction.

Unlike a statutory audit, FDD focuses on the quality and sustainability of the numbers behind the business. Buyers use it to assess earnings, revenue, working capital, debt, liabilities, and financial controls, and the findings can influence valuation, deal structure, negotiations, and contractual protections.

For finance teams, preparation matters. Clean financial records, documented accounting policies, reliable audit trails, and accessible transaction data make it easier to answer buyer questions and reduce the risk of unexpected issues emerging during the process.

This guide explains what financial due diligence covers, the common red flags buyers look for, and how finance teams can prepare before a transaction begins.

Key takeaways

• Financial due diligence (FDD) assesses the quality, sustainability and risks behind a company’s financial performance before an acquisition, investment or other transaction.

• Buyers typically review earnings quality, revenue recognition, working capital, net debt, customer concentration, liabilities and financial controls.

• A well-prepared finance function can make due diligence faster by maintaining reconciled accounts, clear accounting policies, reliable audit trails and accessible transaction records.

• Common red flags include inconsistent financial statements, ageing receivables, aggressive revenue recognition, customer concentration and undocumented liabilities.

• Financial due diligence findings can influence valuation, deal structure, negotiations and the protections included in a transaction.

What is financial due diligence?

FDD is the deep financial investigation a buyer or investor conducts before committing capital to a transaction. It goes well beyond what a statutory audit covers.

Your annual audit asks whether the numbers comply with accounting standards. FDD asks whether a buyer should believe those numbers.

An audit confirms that financial statements are prepared in accordance with FRS 102 or IFRS and present a fair view of the company's position, whereas FDD interrogates the quality, sustainability, and reliability of the underlying numbers, including whether historical growth trends support forward-looking assumptions. It also examines whether:

• Earnings are repeatable

• Revenue recognition reflects economic reality

• Working capital has been window-dressed

• Whether hidden liabilities sit outside the reported figures.

The output is typically a detailed report that directly informs the purchase price, the structure of the deal, and the warranties the buyer will require.

For mid-market companies, FDD is often the most intense financial scrutiny the business has ever faced. The finance team's ability to respond quickly and accurately shapes both the valuation outcome and the buyer's confidence in the business.

Buy-side vs. sell-side: Where mid-market finance teams fit

FDD can be conducted from either side of a transaction.

Buy-side FDD is commissioned by the acquirer or investor. Their advisory team investigates the target company's financials to identify risks, validate the valuation, and inform deal terms. The buyer is asking: "Should we pay this price, and what could go wrong?"

Sell-side FDD is commissioned by the company being acquired. The seller's advisory team conducts the same analysis proactively, identifying and addressing issues before the buyer's team finds them. The seller is asking: "What will buyers find, and how do we strengthen our position before they look?"

For mid-market finance teams, sell-side readiness is where the work lives. You're the team that will field document requests, produce transaction-level data, and defend the numbers under scrutiny. The rest of this guide focuses on what buyers examine during FDD and how your team can prepare for it, because the companies that control the narrative going into a process consistently achieve better outcomes.

How long does financial due diligence take?

A typical FDD process for a mid-market transaction takes four to eight weeks, though timelines vary significantly depending on the complexity of the business, the quality of financial records, and the buyer's requirements.

Straightforward transactions with clean financials and organised data rooms can complete in as few as three to four weeks. Multi-entity businesses, companies with complex revenue recognition, or those with fragmented financial systems often see FDD stretch to ten or twelve weeks as the advisory team often has to work through information gaps or inconsistencies.

The single biggest factor in the timeline is data readiness. Finance teams that can produce complete, well-organised financial records on demand compress the process dramatically. Those that need weeks to locate documents, reconcile accounts, or reconstruct approval trails extend it, and every additional week of delay introduces retrading risk as the buyer's confidence erodes.

What FDD covers: The core review areas

FDD follows a structured framework. Each area below represents a category that the buyer's advisory team will examine in detail, along with the red flags that trigger deeper investigation and the fixes that protect your position.

Financial due diligence review areas at a glance

The exact scope varies by company and transaction, but these areas help buyers understand both the historical financial performance of the business and how reliable and sustainable those numbers are.

Quality of earnings

This is the analysis that determines your valuation multiple. The advisory team strips away one-time items, owner perks, and non-recurring revenue to reveal normalised EBITDA: the number that actually sets the price. A £100,000 reduction in normalised EBITDA on a 10x multiple means a £1,000,000 reduction in purchase price.

Red flag: Normalisation adjustments keep growing as the advisory team digs deeper, suggesting the reported earnings picture is unreliable.

The fix: Maintain a rolling schedule of non-recurring items and adjust your internal reporting, so you always know what your normalised EBITDA looks like before a buyer calculates it for you.

Revenue quality and recognition

Buyers assess whether your revenue is recurring or one-off, whether recognition timing matches actual performance obligations, and whether growth is organic or artificially inflated. High-quality revenue means predictable renewals, consistent recognition policies, manageable churn, and a diversified customer base.

Red flag: Aggressive recognition practices such as large one-time implementation fees, quarter-end pull-forwards, channel stuffing, or discounting patterns that inflate topline results without creating durable value. The most cited European example remains HP's $8.8 billion write-down on its acquisition of UK-based Autonomy, roughly 80% of the price paid. Revenue recognition irregularities went undetected until after close. Closer to home, Wirecard's 2020 collapse exposed €1.9 billion in fictitious cash balances that had survived years of audits, a reminder that even regulated entities in core European markets can harbour fabricated financials. For mid-market companies, the more common version is less dramatic but equally damaging: inconsistent application of recognition policies across contracts or periods.

The fix: Document your revenue recognition policies explicitly (under FRS 102 or IFRS 15), ensure they align with actual practice, and apply them consistently.

Working capital and cash conversion

Acquirers calculate your days sales outstanding (DSO), days inventory outstanding, and days payable outstanding to understand how efficiently revenue converts to cash. Sudden increases in DSO or unusual inventory movements trigger deeper questions, including whether results have been window-dressed ahead of a sale.

Red flag: Ageing receivables. Many deals use formulaic approaches to haircut older receivables in working capital calculations, awarding high credit to current balances and little to none past 90 days. This directly impacts the purchase price.

The fix: Tighten collection processes, write off genuinely uncollectible balances promptly, and maintain current ageing reports that accurately reflect your receivables position.

Net debt and debt-like items

Net debt matters in financial due diligence because it can affect the amount ultimately paid to shareholders.

Buyers typically look beyond headline bank borrowings and cash balances to understand the company's wider financial obligations. Depending on the transaction, this may include loans, overdrafts, accrued interest, lease obligations, unpaid taxes, deferred consideration, and other items treated as debt-like.

What buyers check: Whether borrowings, cash balances, and potential debt-like liabilities have been identified accurately and reflected consistently in the company's financial records.

Red flag: Material liabilities that emerge late in the diligence process or obligations that have not been clearly classified or documented.

The fix: Maintain an up-to-date schedule of borrowings and material liabilities, reconcile balances to the general ledger, and keep supporting agreements readily available.

A clear view of net debt reduces the risk of unexpected adjustments when the buyer moves from enterprise value to the final equity value of the transaction.

Customer concentration

Buyers assess how revenue is distributed across your customer base and react quickly to signs of dependency.

Red flag: Any single customer represents more than roughly 10% of total revenue, or the top five contribute a disproportionate share.

The fix: Concentration cannot be resolved overnight, but it can be mitigated through longer contract terms, multiple contact points within customer organisations, and documented diversification strategies.

Hidden liabilities and off-balance-sheet obligations

These are deal killers because they represent unknown risk.

Red flag: Unrecorded employee liabilities, pending settlements, or deferred revenue that has not been properly accounted for. Bayer's acquisition of Monsanto demonstrates the catastrophic end of this spectrum, where litigation provisions have exceeded $11 billion after underestimating litigation risk.

The fix: Conduct a thorough review of all contingent obligations and recognise liabilities consistently as they arise.

Related-party transactions

Red flag: Undisclosed related-party revenue, non-arm's-length pricing, or expense categories used to bury personal spend. Any of these can quickly become negotiation leverage for a buyer.

The fix: Document every related-party transaction, price at arm's length, and disclose transparently.

Inconsistent financial statements

Red flag: Income statements that do not reconcile with tax returns or the general ledger. Buyers lose confidence in the accuracy of the entire financial record.

The fix: Reconcile every account monthly, correct misclassifications immediately, and ensure every transaction is traceable to source records. That discipline protects your valuation directly.

What common FDD red flags have in common

Many financial due diligence red flags ultimately point to the same underlying problem: buyers cannot easily verify the financial story they have been given.

Common issues include:

• Unexplained adjustments to EBITDA

• Aggressive or inconsistent revenue recognition

• Ageing or potentially unrecoverable receivables

• Significant customer concentration

• Unreconciled balance-sheet accounts

• Undocumented liabilities or commitments

• Related-party transactions that are not clearly disclosed

• Inconsistent accounting policies

• Missing supporting documentation

• Weak approval processes or transaction audit trails

A red flag does not automatically mean a transaction will fail. But unresolved issues can lead to additional questions, valuation adjustments, delays, or greater contractual protection for the buyer.

Strong financial controls help reduce this risk. When transactions are consistently approved, categorised, reconciled, and supported by documentation, finance teams can respond to diligence requests faster and give buyers greater confidence in the underlying numbers.

How audit trails and spend visibility strengthen your FDD position

Buyers want to trace numbers back to individual transactions quickly. Advisory teams consistently flag data accuracy, completeness, and evidence quality as top due diligence challenges, especially when the target relies on manual processes and scattered systems.

The challenge for mid-market companies is that spend data (the transactions flowing through company cards, expense claims, invoices, and procurement) often sits across disconnected systems. During FDD, this fragmentation transforms from an operational annoyance into a valuation risk. The business performs well on paper, yet behind the numbers lie missing documentation, outdated systems, or financial statements that do not tell a cohesive story. Buyers notice.

Approval workflows matter because they create a defensible audit trail: who requested the spend, who approved it, when it was approved, and what documentation supported it. When a buyer's advisory team can trace a transaction from purchase request through approval to payment and receipt in a single system, it removes an entire category of FDD friction.

What this looks like with the right systems

This is where a spend management platform like Spendesk, which consolidates procurement, smart company cards, expenses, invoices, and budgeting into a single system, directly strengthens FDD readiness. Instead of spending weeks reconstructing approval records and hunting down missing receipts, finance teams can produce transaction-level audit trails on demand.

Niji, a 1,500-person digital services company, scaled to 12x their original transaction volume on the platform while improving receipt recovery from 10% to near-complete capture.

Pierre Frey, operating across five international entities, eliminated paper expense claims entirely. In an FDD context, this kind of documentation completeness across entities is precisely what buyers need to see. According to Spendesk, customers report up to an 80% reduction in manual data entry and up to four days saved on month-end close, efficiencies that compound dramatically when an advisory team requests three to five years of granular spend data.

Automated categorisation with rule-based bookkeeping, where expenses are consistently mapped to the correct accounts based on supplier and transaction type, eliminates miscategorisation risk systematically rather than through periodic manual clean-up. The shift from reactive documentation to real-time, policy-compliant spend capture makes your financial story verifiable and consistent. That is exactly what acquirers are looking for.

FDD readiness checklist for mid-market finance teams

Whether a transaction is imminent or years away, the following checklist builds the financial infrastructure that protects valuation and accelerates any future process. The underlying principle is consistent: build systems that enforce policy and capture documentation automatically, so your team is not reconstructing records under pressure.

Quick-reference checklist

• Material balance-sheet accounts are reconciled and unexplained variances investigated

• Revenue recognition policies are documented and reflect actual accounting practice

• Supporting workpapers are available for material balance-sheet accounts

• Significant customer concentration is identified and understood

• Related-party transactions are documented and appropriately disclosed

• Personal and business expenditure is clearly separated

• Month-end close is completed consistently with supporting reconciliations

• Spend approval workflows and transaction documentation are maintained

• Material uncategorised or unexplained expenditure has been investigated

• Debt agreements and significant contractual obligations are documented

• A virtual data room structure is prepared

• Material liabilities and debt-like items are documented

• An internal FDD readiness review has been completed before a formal process begins

How to prepare for financial due diligence

Preparing before a transaction begins gives finance teams time to identify gaps and resolve them before they become buyer concerns.

The goal is not simply to produce more documentation. Finance teams should be able to explain where the numbers come from, how financial decisions are controlled, and why the information presented to buyers is reliable.

Building these habits before a transaction also has operational benefits. Cleaner records, stronger controls, and accessible transaction data support faster reporting and reduce the amount of manual work required when external advisers begin requesting information.

Spendesk's all-in-one platform gives finance teams full spend visibility and control across cards, invoices, and expenses: the kind of end-to-end documentation trail that makes FDD faster and less risky for both sides.

Frequently asked questions about financial due diligence

What is the difference between financial due diligence and an audit?

An audit confirms that financial statements comply with accounting standards such as FRS 102 or IFRS. FDD goes further, examining whether the numbers are reliable, sustainable, and free from hidden risks that would affect a transaction. Auditors assess compliance; FDD advisory teams assess investability.

Who conducts financial due diligence?

FDD is typically conducted by specialist advisory teams at accounting or corporate finance firms. In the UK, the Big Four (Deloitte, PwC, EY, and KPMG) handle large transactions, while mid-market deals are often led by mid-tier firms with dedicated transaction services practices. The buyer commissions buy-side FDD; the seller may commission a separate sell-side report to control the narrative.

What is included in a financial due diligence report?

A standard FDD report covers quality of earnings (normalised EBITDA), revenue sustainability and recognition, working capital analysis, net debt assessment, customer and supplier concentration, hidden liabilities, related-party transactions, and financial statement integrity. The report typically concludes with a summary of key findings and their implications for the purchase price and deal structure.

What documents are needed for financial due diligence?

Financial due diligence usually requires several years of financial and operational information. The exact request list depends on the transaction, but companies are commonly asked to provide:

• Historical financial statements and management accounts

• Trial balances and general-ledger data

• Revenue and customer analysis

• Accounts receivable and payable ageing

• Working-capital information

• Debt and cash schedules

• Budgets and financial forecasts

• Tax information

• Material customer and supplier contracts

• Accounting policies

• Details of related-party transactions

• Supporting records for significant or unusual transactions

Keeping these records organised before a transaction begins reduces the administrative burden once formal diligence starts.

How much does financial due diligence cost?

The cost of financial due diligence varies considerably according to the size and complexity of the transaction, the scope of the review, the number of entities involved, the quality of the available financial information, and the advisory firm conducting the work. Rather than relying on a standard benchmark, companies should agree the scope and expected fees with their advisers before the process begins.

Can you do financial due diligence yourself?

Internal finance teams can and should conduct their own readiness assessment before engaging external advisors. This includes reconciling all accounts, documenting recognition policies, reviewing related-party transactions, and building a virtual data room. However, formal FDD for a transaction requires independent, qualified advisory teams whose findings carry credibility with buyers and their legal counsel.

What are the biggest financial due diligence red flags?

Common financial due diligence red flags include unexplained EBITDA adjustments, inconsistent revenue recognition, high customer concentration, ageing receivables, hidden liabilities, unreconciled accounts, and weak financial controls.

Buyers may also investigate significant margin fluctuations, unusual related-party transactions, and inconsistencies between management reporting and statutory accounts.

The impact depends on the nature and materiality of the issue. Some findings require only clarification, while others can affect valuation, deal structure, or the protections requested by the buyer.

How should a company prepare for financial due diligence?

Companies should prepare for financial due diligence by ensuring their financial records are accurate, reconciled, and supported by clear documentation.

Finance teams should review material balance-sheet accounts, revenue recognition, working capital, customer concentration, debt, significant liabilities, and related-party transactions. Approvals, invoices, payments, and accounting records should also be traceable through a reliable audit trail.

Running an internal readiness review before formal diligence begins gives the company time to identify, correct, or explain potential issues before they are raised by a buyer.