What Is a Proof of Cash in M&A Due Diligence?

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 When you buy a company, the hardest part is knowing if the numbers are real.

The seller’s financials might look fine on paper, but paper is cheap. What you really want to know is: how did the money actually move?

That’s where a proof of cash comes in.

A proof of cash is simple. It lines up the company’s bank statements against its financial statements. Every deposit, every withdrawal, every ending balance. Instead of sampling a few transactions, this is a full sweep of all cash inflows and outflows.

So why does this matter?

Errors or inconsistencies in financial statements can come from mistakes or “mistakes.”

Either way, a proof of cash will catch them.

For example, unrecorded transactions or mismatched balances can point to:

• Revenue overstatements
• Undisclosed liabilities
• 
  

These are the kinds of issues that quietly distort a deal if they go unchecked.

For many buyers, revenue is the number.

If reported revenue isn’t showing up in the bank, you have a problem. The same applies to expenses. If the cash isn’t there, the story likely isn’t either.

This comes up often in businesses with messy books.

For example, in a cash-heavy business or one transitioning from cash to accrual accounting, it’s common to see timing issues or incomplete records. A proof of cash helps separate what’s real from what’s just recorded.

Most buyers start skeptical, which is a good place to be.

The goal is to replace that skepticism with something grounded. A proof of cash does that by tying everything back to actual transactions.

When you can trace the numbers to real cash movement, negotiations tend to move more smoothly.

In a quality of earnings (QoE) report, proof of cash is both a foundation and a stress test.

It supports revenue and expense trends and strengthens the overall financial narrative.

If a company claims revenue doubled year over year, the bank should show the same pattern.

If it doesn’t, you know exactly where to start digging.

A proof of cash validates whether reported growth is backed by real cash inflows. It can also surface issues like revenue being recorded without corresponding deposits.

Imagine a buyer evaluating a transportation company that is transitioning from cash to accrual accounting.

The financials show $50 million in annual revenue. On paper, the growth looks strong.

But during diligence, a proof of cash shows gaps between reported revenue and actual deposits. Some invoices are being recorded as revenue before the cash is collected.

After adjusting for this, the buyer ends up with a more accurate view of both valuation and cash flow.

Do it early
Running a proof of cash early in the process can prevent surprises later on.

Use it to align expectations
When both sides are working from numbers backed by real cash, conversations become more straightforward.

Pair it with other analyses
A proof of cash is powerful, but it’s not the full picture. It works best alongside checks like payroll reconciliation and book-to-tax reconciliation.

A proof of cash is the x-ray of financial due diligence.

It connects financial statements to bank activity and gives you a clearer view of what’s actually happening in the business.

Whether you’re evaluating a small business or a larger transaction, having this level of visibility makes it easier to move forward with confidence.

At QOE Prep, proof of cash is one step in understanding what’s really going on behind the numbers. If you’re working through a deal and want a clearer picture, I’m happy to talk it through.