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

Financial due diligence (FDD) determines how much your company is worth in a transaction. Every review area, from earnings quality to working capital to hidden liabilities, either protects your valuation or erodes it. The difference between the two almost always comes down to preparation.

An analysis of 40,000 acquisitions over four decades found that 70% to 75% fail to achieve their stated objectives, with overvaluation and integration failures showing up repeatedly as leading contributors. In the UK mid-market, buyers have become more cautious following interest rate volatility and last year's Autumn Budget which brought with it Capital Gains Tax and employer NIC changes. FDD processes have stretched, and the bar for financial readiness has risen with them.

This guide covers what FDD involves, what buyers scrutinise, the red flags that derail deals, and how mid-market finance teams can build readiness before a process begins.

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.

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.

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.

The pattern behind most red flags

Every red flag above puts the finance team in the same bind. Lock down spending with rigid manual controls and you become the bottleneck. Every purchase order routes through the Finance Controller's inbox, month-end close stretches because you're the only person who can approve corrections, and buyers flag key-person dependency in their report. Loosen controls to keep the business moving and you get gaps: missing receipts, unapproved subscriptions, expense categories nobody can explain, and buyers flag weak oversight instead.

Acquirers don't want either version. They want systematic spend control: policies enforced automatically, approvals routed by rules rather than by habit, and documentation captured at the point of transaction rather than reconstructed weeks later.

That's a solvable problem, and solving it before a process begins materially reduces retrading risk.

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

• All balance sheet accounts reconciled with no unexplained variances over £5,000

• Revenue recognition policies documented in writing and verified against actual practice

• Dedicated workpapers explaining each balance sheet's account balance

• No customer representing more than 10% of revenue without documented mitigation

• All related-party transactions documented with arm's-length pricing

• Personal and business expenses fully separated with adjustments documented

• Month-end close completing within five business days

• Spend approval workflows automated with receipts captured at point of transaction

• "Miscellaneous" and "uncategorised" expense categories eliminated

• All debt agreements reviewed for change-of-control provisions

• Virtual data room structure built and maintained

• Sell-side Quality of Earnings analysis completed or scheduled

The detailed roadmap

Start this month. Reconcile every balance sheet account and resolve any unexplained variances over £5,000. Document your revenue recognition policies in writing and verify they match actual practice. Ensure you have dedicated workpapers explaining each balance sheet account balance. Designate a single point of contact who would handle document requests if a transaction materialised, and review your file naming conventions so you can find and produce documents quickly.

Within three months. Identify any customer representing more than 10% of revenue and document mitigation strategies. Review all related-party transactions for arm's-length pricing. Separate any commingled personal and business expenses and document the adjustments. Establish a month-end close process that targets completion within five business days and produces investor-grade management accounts.

Within six months. Implement real-time spend tracking that captures approval workflows, receipt documentation, and categorisation as transactions happen, not weeks later. This is where centralised visibility over decentralised spending pays for itself: every employee can spend within policy, every transaction is documented automatically, and finance does not become the bottleneck chasing receipts and approvals after the fact. Eliminate "miscellaneous" and "uncategorised" expense categories entirely; they signal weak control and make it harder to defend your numbers. Review all debt agreements for change-of-control provisions. Build a virtual data room structure that mirrors how professional buyers conduct FDD, with a clear top-level folder hierarchy and consistent naming.

Within twelve months. Commission a sell-side Quality of Earnings analysis to identify and address normalisation adjustments before a buyer finds them. Strengthen internal controls around revenue recognition, approvals, and segregation of duties to reduce your representations and warranties exposure during negotiations. Run a mock FDD exercise, treating it like a dry run of your audit preparation, by inviting a third party to review your materials and identify gaps.

Quarterly, ongoing. Can you produce a complete data room in 48 hours? Are all reconciliations current? Do revenue recognition policies still match practice? Have customer concentration metrics improved or deteriorated? Then you're on the right track.

Done consistently, this cadence turns FDD from a one-off scramble into business-as-usual. The same disciplines that make your finance function run efficiently (clean categorisation, real-time visibility, and policy-compliant spend capture) are precisely what acquirers evaluate when they assess financial control quality. The finance teams that treat readiness as a continuous discipline do not just protect valuation. They run better organisations, close books faster, and spend their time on analysis and strategy rather than chasing documentation.

FDD rewards preparation, not performance under pressure. Faring well in a transaction comes easily to teams who built their infrastructure, documentation habits, and spend controls long before an acquirer came around. Start with what you can fix this month, and the rest follows.

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.

How much does financial due diligence cost?

Costs vary significantly by deal size and complexity. For mid-market UK transactions, FDD fees typically range from £30,000 to £150,000 or more, depending on the scope, the number of entities, and the advisory firm. Sell-side FDD tends to be less expensive than buy-side because the seller controls the information flow and can manage scope more tightly.

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.