What it means
A supplier sends an invoice, but payment may wait while a buyer confirms the goods, a project lead checks work or finance resolves a price mismatch. If the approval queue is slow, the business may miss an agreed payment date or early-payment discount.
Lag shows how long each step takes rather than blaming finance for every late payment. Select whether elapsed time means calendar time or working time, then state the choice; APQC, for example, has a receipt-to-approval measure in calendar days, and an internal workflow can use another clock if it is consistently labelled.
Define the start and end points, since some teams start when a valid invoice is received and others when it is entered into the system. A scanned invoice sitting in an inbox for five days should not disappear from a customer or supplier experience measure just because the workflow started later, so report receipt-to-entry and entry-to-decision separately if needed.
Use a stage-level dashboard to separate supplier correction, internal receipt confirmation and authorised approval, because a long total can result from a real dispute rather than an idle manager. Track the oldest open exceptions and document the reason.
Classify outcomes too, since approved, rejected, queried and returned for correction are not the same, and an invoice disputed with a supplier can stay open for a legitimate reason. Show the owner and age of each item, and do not mark it approved to clear a queue while the mismatch remains.
Approval authority matters: a manager may confirm the service but lack spending authority, and a substitute approver during leave can reduce avoidable delay if delegation is documented. Automatic rules can handle low-risk exact matches, while unusual amounts or changed bank details need stronger checks.
Compare lag with contractual payment terms, because a ten-day approval might be fine for a 60-day term and harmful for a seven-day term. Consider the cash forecast and supplier relationship, not only a generic target.
Ageing bands reveal long-tail exceptions hidden by an acceptable average. For managers, the metric should lead to a clear next action: supply missing evidence, reassign a valid approver or resolve a dispute.
Faster approval is not worth paying the wrong amount.
In practice
Real-world examples.
Example
An invoice received on Monday waits three days for goods-receipt confirmation before an authorised buyer approves it. The workflow shows the lag as three days, split into one stage for receipt and one for approval. The buyer can see exactly where the wait occurred.
Example
A project manager rejects a contractor invoice with an unsupported variation, and the workflow records a dispute rather than a late approval. The contractor receives a clear request for evidence. The reject-to-resubmit time is reported separately.
Example
A vacationing approver delegates within the company's policy so matching invoices do not sit idle for two weeks. The delegate's authority limit is recorded in the system. When the approver returns, the delegation ends automatically.
Formula
Calculation
Approval lag = Authorised approval decision timestamp - Defined workflow start timestamp
Average approval lag = Sum of lags for comparable decided invoices / Number of those invoices
Worked example. Five fictional valid invoices have approval lags of 1, 2, 3, 4 and 10 days.
- Average = (1 + 2 + 3 + 4 + 10) / 5 = 20 / 5 = 4 days.
- Median = 3 days, the middle value. The ten-day case should still be reviewed; the average alone hides it.
Now compare lag with terms. On a 60-day term, a ten-day approval leaves 60 - 10 = 50 days for payment processing. On a seven-day term, the same ten-day approval means the invoice is already 10 - 7 = 3 days late before payment is even scheduled.
Open or disputed invoices need their own ageing report rather than being silently dropped from performance review.Case study
Seen in the real world.
This illustrative and entirely fictional example follows Bayline Facilities, an invented maintenance buyer. Suppliers complained about late payments even though finance processed approved invoices within a day. A review showed invoices waited on site managers for service confirmation, with no substitute approver during leave. Bayline separated receipt, entry, service verification and final approval timestamps.
It set delegated authority for routine verified work and a clear route for disputed lines. Finance then paid correctly approved invoices on the agreed schedule and showed suppliers which items genuinely needed correction. The company did not remove verification just to make the metric faster. It removed avoidable waiting and made real disputes explicit.
Its monthly report showed both completed decisions and the old invoices still open. That prevented a faster average from disguising unresolved exceptions. Suppliers also saw a single named contact for each stuck invoice, which reduced repeat chasing emails to the finance team.
Watch out
Common mistakes.
- Starting the clock only after data entry while invoices sit unseen in an earlier inbox.
- Counting a disputed invoice as approved to improve the metric, then paying an unsupported amount.
- Reporting only an average without tracking old open items and the stage causing delay.
Questions
People also ask.
Is approval lag the same as days to pay?
No. Approval is one stage; contractual due date, payment run and bank settlement affect total payment time.
Should rejected invoices count?
Track time to a decision and outcome separately. A justified rejection is not a successful approval.
Can exact-match invoices be auto-approved?
Some systems permit it within controlled limits. Check the matching evidence, authority and exception rules.
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