Measuring AP

Cost per invoice

Cost per invoice = total AP cost for a period ÷ invoices processed in the same period. Use a fully loaded cost: AP staff salaries with benefits, the share of managers’ and approvers’ time spent on invoices, software and payment fees, and overhead allocated to AP. Count every invoice processed, including credit memos and invoices that were reworked.

Ardent Partners’ State of ePayables 2025 puts the average all-in cost at $9.84 per invoice, $2.65 for Best-in-Class teams and $12.42 for all others. The example team is close to the average. Benchmarks are all-in figures, so compare them with a fully loaded number, not salaries alone.

Invoice exception rate

Exception rate = invoices with at least one exception in a period ÷ total invoices processed in that period × 100. Count an invoice once even if it has several problems, so the rate stays comparable month to month. For example, 230 invoices with exceptions out of 1,250 processed is an 18.4% exception rate. (Illustrative numbers.)

Ardent reports an average exception rate of 18.4%, 11.1% for Best-in-Class teams and 20.9% for all others. Its related measure, the straight-through rate (invoices approved with no human touch), averages 35.4%, and 51.0% for Best-in-Class teams. Best-in-Class teams also link far more invoices to purchase orders, 84.0% against 47.3% for all others, which gives matching something to check against.

Exceptions are usually the biggest driver of cost per invoice, because each one is manual research and rework. Tagging every exception with a cause, as in Module 3, tells you which fix to make first.

Days payable outstanding (DPO)

DPO = average accounts payable ÷ cost of goods sold (or operating expenses) × 365. It measures how long, on average, you take to pay suppliers. Average accounts payable is usually the opening plus closing AP balance for the period, divided by two.

For example, a business with average accounts payable of $400,000 and annual cost of goods sold of $3,650,000 has a DPO of 40 days: $400,000 ÷ $3,650,000 × 365. (Illustrative numbers.)

APQC puts the median DPO at around 40 days across industries, with about 30 days at the 25th percentile and about 50 days at the 75th. The J.P. Morgan Working Capital Index 2024 reported 51.2 days across the S&P 1500 (excluding financials and real estate) in 2023. DPO varies widely by industry, so compare with your own sector using the DPO by industry report.

Higher is not automatically better. A higher DPO keeps cash in the business, but past agreed terms it becomes late payment, which costs supplier goodwill and any early-payment discounts you could have taken. That is why DPO only means something next to a correct AP balance, which is what the Module 6 reconciliation gives you.

Other KPIs worth tracking

How to set up tracking

1. 1

   Pick a few KPIs

   Start with cost per invoice, exception rate and DPO; add cycle time once those are stable.

2. 2

   Fix the definitions

   Write down each formula and data source so the number means the same thing every month.

3. 3

   Measure a baseline

   Take three months before setting any target.

4. 4

   Compare with one source per KPI

   Definitions differ between benchmark publishers, so do not mix them.

5. 5

   Review monthly

   When a KPI moves, record why. If you change a definition, restate earlier months so the trend stays honest.