An accounts payable outsourcing case study usually ends on two figures, the share of invoices processed without a person touching them and a cost cut. Neither one says what an invoice cost before, how long it sat between arrival and approval, or who was still allowed to release the money.
Accounts payable (AP) has its own units, and a case written in seat costs has changed the subject. Two questions decide whether a published result means anything for your firm: did it report in AP's own units, and did the controls that make a payment safe stay where they belong.
What Accounts Payable Outsourcing Actually Covers
Accounts payable outsourcing is an arrangement where an outside team takes the record work of the payables cycle, receiving invoices, coding them, matching them against purchase orders and delivery records, and preparing the payment run, while approval and the release of money stay with the buying firm. Where a provider also holds approval or release, that is a different arrangement carrying different risk, and it should be described as one rather than sold under the same name.
A case built on that arrangement has four parts. It names the client and the shape of its payables. It states the before position and how that position was measured. It says which steps moved and which stayed inside. It reports the result in AP's own units rather than in headcount. The middle two parts decide whether the result transfers to your firm, and they are the two most likely to be missing.
Report an Accounts Payable Outsourcing Case Study in Invoices, Not Seats
The unit of AP is the invoice. Every claim about the function should reduce to what one invoice costs to process and how many an experienced person can carry.
Cost per invoice is total AP cost for a period divided by the invoices processed in that same period. The total is the part people get wrong. It includes the software, the exception handling, the hours controllers and partners spend chasing approvals, and the review that stayed behind, not only the wage of whoever keys the invoice.
Invoices per full-time equivalent (FTE), meaning one person on a full schedule or several part-time people adding up to one, is the capacity half of the same picture. That is the figure that tells you whether the next wave of volume needs another hire.
Both move for reasons no provider controls. Invoice volume rises, the mix shifts between invoices backed by a purchase order and invoices arriving without one, a single large client changes how it bills. The pair only reads honestly across matched periods, and a case that reports one without the other has described effort or cost, never both.
The wider trap of a percentage with no base is worked through in reading a CPA firm outsourcing cost savings case study, and it applies here unchanged.
Invoice Cycle Time Runs From Receipt to Approval, and Both Ends Are Arguable
Invoice cycle time is the elapsed time from an invoice arriving to that same invoice being approved and scheduled for payment. It is the metric most often quoted and least often defined, because both endpoints can be moved.
The Clock Does Not Start Just Because an Invoice Arrived
Federal payment rules settle the start in a way worth copying. Under the Prompt Payment rule, the period available to an agency to make timely payment without an interest penalty "shall begin on the date of receipt of a proper invoice" (5 CFR 1315.4(f)). Those rules bind federal agencies paying their vendors, not your firm or your clients, so borrow the definition and leave the obligation.
Read that alongside the paragraph it points to, because receipt is a defined event rather than a delivery time. An invoice is deemed received on the later of two dates, the day a proper invoice actually reached the office that receives it, or the seventh day after the property was delivered or the services were completed, with an earlier acceptance date substituting for that seventh day, and with the date of actual acceptance or the end of a longer contractual acceptance period substituting where the contract sets one (5 CFR 1315.4(b)). That is the half worth copying. It stops the clock running before anyone has confirmed the work was done, which is the one place an arrival-stamped cycle time can be made to look good for free.
The same rules define "proper", which is what stops the definition being circular. A proper invoice carries the name of the vendor, the invoice date, an authorization for the goods or services, the vendor's own invoice or account number, a description with price and quantity, shipping and payment terms, a contact name and telephone number where practicable, and whatever other substantiating documentation the contract requires (5 CFR 1315.9(b)(1)). Two more sit on that list unless agency procedures provide otherwise, the Taxpayer Identifying Number (TIN) and the vendor's banking information. Those two are the ones that come back in January and in a fraud review, and they are the two a service agreement has to name rather than assume.
The Far End of the Clock Is Looser Still
A result can stop the measurement when the approver clicks, when the invoice posts, or when the payment run goes out, and in the same month those three events can sit days apart. Ask which one ends the count before you read the number.
There is also a rule for the invoices that leave the pipeline instead of finishing it. An improper invoice is returned to the vendor as soon as practicable, and no later than 7 days after receipt, with every defect that prevents payment identified (5 CFR 1315.4(c)(2)). Without a rule of that kind, cycle time improves by holding bad invoices out of the count, so a result quoting cycle time should also say what happened to the invoices that never entered it.
Touchless Rate and Exception Rate Have to Be Read Together
A touchless invoice goes from arrival to posting without a person intervening. An exception is narrower, an invoice that needed a human decision because the price did not match, the coding was ambiguous, the vendor was unknown, or the goods receipt was missing. A goods receipt is the record confirming what was actually delivered, so a missing one means nobody can yet tell whether the invoice should be paid at all.
The gap between the two figures is manual work that raised no question, an invoice keyed by hand that then matched cleanly. That work is not touchless and it is not an exception, which is why a rising touchless rate and a flat exception rate can both be true in the same month.
Read them together or not at all. Moving exceptions into a separately named queue raises the touchless rate on the invoices that remain while the same work sits in the same place, which is why the two figures have to share a denominator and a period.
The useful version also reports what caused the exceptions. An AP function whose exceptions are mostly missing goods receipts has a purchasing problem, and nobody is going to fix that from the payables side.
Recovered Money, Captured Discounts and the Cash You Paid Early
Three more figures show up in AP results, and each one hides a decision that belongs to the firm rather than the provider.
A Recovery Number Describes the Leak, Not the Repair
Duplicate and erroneous payment recovery is the most flattering figure in AP, because it arrives as found money. It is also backwards. Recovering a duplicate means the duplicate was made, so the number to ask for is how many duplicates were created per thousand invoices before and after, next to whatever was clawed back.
Ask who found them as well. A recovery that surfaced because the vendor called to return the money is not evidence of a control.
Discount Capture Has a Rule Worth Copying
Early payment discount capture is the share of available discounts actually taken. The Prompt Payment rule makes that decision explicit. An agency may take a discount "if economically justified" and only after acceptance has occurred, payment is made as close as possible to but no later than the discount date, and the discount period is calculated from the date the vendor placed on the invoice, or from the date a proper invoice was received and date stamped where the invoice carries no date (5 CFR 1315.7).
That last clause is the one to write into a service agreement. Where the vendor left the invoice undated, whoever date stamps it sets the discount clock, so a provider that stamps late hands itself a later deadline and a better looking capture rate. Where the invoice carries a date, the stamp moves nothing, and every day between arrival and processing comes straight out of the time available to take the discount. Say in the agreement which date starts the count and who records it.
Days Payable Outstanding Is Not the Same Decision as Cycle Time
Days payable outstanding (DPO) is the average time payables stay unpaid. A faster approval cycle only shortens it where the firm pays on approval. Where payment runs on the vendor's terms, approval gets faster and DPO does not move at all.
Hold that distinction, because where DPO does fall, cash leaves earlier, and that is a cost no cycle time chart shows. A credible AP result reports cycle time and DPO together, and says which way the firm wanted each to move. Speed to approval and speed to payment are separate decisions, and only the first one belongs to the provider.
The Control Boundary That Separates a Saving From a Liability
An AP saving is legitimate only if the controls that survived it are the ones that matter. Three of them decide the answer.
Preparer and Approver Have to Stay Different People
Segregation of duties, the practice of splitting a transaction so no single person carries it end to end, is the control an AP saving is most likely to erode. The federal internal control standards state it plainly: management "considers segregation of duties in designing control activity responsibilities so that incompatible duties are segregated and, where such segregation is not practical, designs alternative control activities to address the risk" (GAO, Standards for Internal Control in the Federal Government, 10.12).
The same standard names which duties. Management "considers the need to separate control activities related to authority, custody, and accounting of operations", and that separation also addresses the risk of management override, though the standard is explicit that management "cannot absolutely prevent it because of the risk of collusion, where two or more employees act together to commit fraud" (GAO, Standards for Internal Control in the Federal Government, 10.13). Written for federal entities, the reasoning still transfers. An outsourced team can hold the accounting. It should not also hold authority or custody.
Payment Release and the Vendor Master File Stay Inside the Client
The vendor master file is the standing record of who each supplier is and where its money goes. Preparing a payment run is record work and it moves cleanly, along the same line between record work and judgment set out in which accounting tasks to outsource. Releasing the payment and editing the master file are not record work, and both stay with the client firm.
Keep those two apart from each other as well. Whoever can add a bank account and whoever can approve a payment should be two people, or the segregation you kept is only half there.
Vendor Impersonation Is the Fraud a Faster Cycle Amplifies
Business email compromise (BEC) is the FBI's name for a scam aimed at businesses and individuals making a transfer of funds, usually carried out after someone gains access to a legitimate business email account (FBI, business email compromise).
The scale is the reason it belongs in an AP conversation rather than an IT one. Reported BEC losses reached $3,046,598,558 in 2025, the second largest loss category in the FBI's own tally for the year (FBI, 2025 IC3 Annual Report).
A faster payables cycle helps that fraud, because the invoice carrying new bank details clears approval before anyone reads the sending domain closely. The countermeasure is procedural. A bank detail change is verified by calling a number already on file rather than one printed on the invoice or sitting in the email thread, and whoever makes that call cannot be the person who approves the payment.
Ask any provider what its own bank change procedure is, then ask when it was last tested rather than where the policy is written.
SOC 1 and SOC 2 Answer Different Questions About a Payment Process
What a SOC 2 report covers, and why a badge on a website is not that report, is already set out in whether outsourcing accounting is safe. The AP-specific point is a different one: which report answers the question payables actually raises.
The AICPA describes SOC 1 as reporting on "controls at a service organization that are likely to be relevant to user entities' internal control over financial reporting" (AICPA, SOC 1). A team preparing your payment runs sits inside that financial reporting path rather than beside it. For a tax preparation seat, where the output is a draft return your reviewer signs off before anything leaves the firm, the security question and the financial reporting question sit close together. For payables, where the output feeds a disbursement, they separate, and a report about how a provider protects data has not answered how that provider's work behaves inside your controls.
The other half of any such report is your own work. The federal internal control standards note that where a service organization's controls are necessary, the entity's own controls may include "complementary user entity controls identified by the service organization or its auditors" (GAO, Standards for Internal Control in the Federal Government, OV4.02). Read that list closely, because it names the things you have to keep doing for the provider's controls to work at all.
Accountably's controls are SOC 2-aligned rather than examined, and what that shifts onto a firm assessing us is priced out in the hidden costs of outsourcing.
Vendor File Completeness Is a January Problem You Measure All Year
The vendor master file is also where next January's information returns are won, and it is measurable during the engagement rather than at the deadline.
The Validation Step and Who Is Allowed to Run It
The measure is the share of active vendors whose name and taxpayer identification number combination has been validated, which in practice starts with a Form W-9 on file. The IRS runs the validation step itself and describes it directly: "The TIN Matching service lets you validate TIN and name combinations before submitting an information return" (IRS, TIN Matching).
Access to it is not open. The same page says TIN Matching is only for payers and their authorized agents that submit information returns, and that a payer must be listed in the IRS Payer Account File (PAF) database (IRS, TIN Matching). Settle who is enrolled before an outsourced team is asked to own the number.
Scope the Rate to the Vendors It Actually Covers
Skipping the check carries a price with a number on it. Where a payee does not give the payer a TIN in the required manner, or the IRS notifies the payer that the TIN given is incorrect, "the payer must withhold at a flat 24% rate" (IRS, Topic no. 307).
That duty is narrower than it sounds. Backup withholding reaches "most kinds of payments reported on Form 1099" (IRS, Topic no. 307), which in a payables ledger usually means contractor fees, rents, royalties and gross proceeds paid to an attorney rather than merchandise.
Payments to a corporation are generally not reportable at all. The exceptions that matter in a payables ledger are payments for legal services, gross proceeds paid to an attorney, and medical and health care payments (IRS, Instructions for Forms 1099-MISC and 1099-NEC). Scope the completeness measure to the vendors whose payments are reportable, or the rate is counting the wrong denominator.
Vendor documentation for backup withholding is also a separate file from the documentation your firm keeps on an offshore provider as a foreign payee, which has its own forms and its own renewal dates in the hidden costs of outsourcing.
Which payments require an information return at all, and at what threshold, is handled in which accounting tasks to outsource. What belongs in an AP engagement is the completeness rate, sitting in the monthly reporting pack beside the invoice counts. A team measured only on throughput will process invoices around a missing W-9 all year.
Accounts Payable Outsourcing for Accounting Firms
Firms meet two versions of this decision, and they are not the same purchase. The first is your own firm's payables, where you are the same buyer as any other business. The second is the AP you run for clients inside a client accounting services (CAS) practice, meaning the outsourced finance function a firm delivers under its own brand. The receivables side splits the same way, as comparing accounts receivable outsourcing companies works through.
In that second case your firm is the service organization, and every boundary above is one you are being trusted to hold, multiplied by the number of clients. Each client has its own approvers, its own vendor master file, and its own rule about who may change a bank account. A single AP process applied flat across all of them is the thing that fails first.
That is why the case study worth having is not one you can read. Run it on one quarter of one client's payables, capturing cost per invoice, cycle time, exception rate and vendor file completeness before a small block of work moves and again after, with payment release and the vendor master file untouched on both sides. If the boundary held and those four numbers moved, that is the only AP case study that decides anything.
Accountably places trained offshore accountants and tax preparers inside US CPA and EA firms, ramped on your software and SOPs in about 3 to 4 weeks. Since 2022 that is 20+ US firms and 30+ placements. Don't trust us. Test us. Run the Free 40-Hour Proof Pilot on a block of your own payables work and grade the output yourself. If a placement is not the right fit in the first 30 days, we replace them free.