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Last updated: September 8, 2026
Your DSO looks fine. Your aging report looks fine. And yet the cash that should have landed this month didn't. That gap is exactly what the Collection Effectiveness Index (CEI) was built to expose: not how fast you collect, but how much of what you could have collected you actually did.
This guide explains what CEI is, how to calculate it without tripping over the formula, what a good score looks like, and how AI-driven collections teams push it above 90% without hiring more collectors.
Table of contents
- What is the Collection Effectiveness Index?
- The CEI formula, step by step
- CEI vs. DSO: why you need both
- What is a good CEI?
- Why CEI drops (and what it's really telling you)
- How to improve your Collection Effectiveness Index
- FAQ
What is the Collection Effectiveness Index?
The Collection Effectiveness Index is the percentage of collectible receivables that your team actually collected during a period, usually a month. It answers a simple question: of every dollar that was available to bring in, how many did we bring in?
That framing matters because it isolates the collections team's performance from sales volume and payment terms. A company can post a healthy DSO simply because its terms are short; CEI ignores that and looks at execution. Finance leaders have noticed. In a Versapay survey, 42% of business and finance leaders ranked CEI among their three most important accounts receivable KPIs.
CEI is also a quality metric, not a speed metric. It rewards teams for leaving as little collectible money on the table as possible, which is why it pairs naturally with the work you're probably already doing on reducing DSO.
The CEI formula, step by step
The formula looks intimidating because it has four inputs. Once you understand what each one represents, it's arithmetic.
CEI formula
CEI = (Beginning AR + Credit sales − Ending total AR) ÷ (Beginning AR + Credit sales − Ending current AR) × 100
The four inputs
| Input | What it means | Where to find it |
|---|---|---|
| Beginning AR | Total open receivables on day one of the period | Prior period's closing AR balance |
| Credit sales | Invoices issued on credit during the period | Billing or ERP sales journal |
| Ending total AR | All open receivables at period end, current and overdue | Closing AR balance |
| Ending current AR | Open receivables at period end that are not yet due | "Current" bucket of the aging report |
The numerator is the cash you collected. The denominator is the cash you could have collected, because invoices that aren't due yet were never fair game. That's the whole trick: CEI only holds you accountable for what was collectible.
A worked example
Suppose you start the month with $300,000 in AR, invoice $200,000 on credit, and end the month with $310,000 in total AR, of which $200,000 is still current (not yet due).
Numerator: 300,000 + 200,000 − 310,000 = 190,000. Denominator: 300,000 + 200,000 − 200,000 = 300,000. CEI = 190,000 ÷ 300,000 × 100 = 63.3%.
In other words, more than a third of the money that was collectible this month is still sitting in past-due buckets. That's the kind of number a DSO report can hide, and both Versapay and HighRadius use a near-identical scenario (landing around 64%) to illustrate an AR process that needs attention.
CEI vs. DSO: why you need both
DSO measures time: how many days, on average, it takes to turn an invoice into cash. CEI measures quality: what share of collectible receivables you converted. They move independently more often than people expect.
- Low DSO, low CEI. Most customers pay on time, but a stubborn tail of overdue accounts never gets worked. Your averages look good; your bad-debt reserve keeps growing.
- High DSO, high CEI. Your terms are long (net 60 or net 90), so cash arrives late, but almost everything collectible gets collected. The fix here is commercial (terms), not operational.
- Both deteriorating. A capacity or process problem. Collectors are missing follow-ups, disputes aren't being resolved, or invoices are going out late or wrong.
Reporting both metrics side by side tells you whether the lever is speed or coverage, and that determines whether you fix payment terms, invoice accuracy, or the follow-up cadence itself.
What is a good CEI?
The closer to 100% the better, but 100% is unrealistic for any business selling on credit. Published benchmarks cluster in a narrow range: Versapay considers 80% or above good, while HighRadius sets the "good" threshold at 85% or higher, treating anything below as a sign of collection issues.
Key takeaway
Treat 80% as the floor, 85% as competent, and 90%+ as best-in-class. But benchmark against your own history and your industry first: a distributor with net-90 terms and a SaaS company billing card-on-file are not playing the same game.
Two caveats. First, CEI is sensitive to period length; a monthly CEI will swing more than a quarterly one because a single large late payment moves the needle. Second, credit sales must cover the same window as the AR balances, or the ratio is meaningless.
Why CEI drops (and what it's really telling you)
A falling CEI is a symptom. The disease is almost always one of five things, and each points to a different fix.
1. Invoices go out late or wrong
A customer cannot pay an invoice they haven't received, and won't pay one with the wrong PO number. Both push collectible cash into the overdue bucket through no fault of the collector. If disputes and short pays are a recurring drag, the deduction management playbook covers how to recover that cash.
2. Lenient credit policy
Approving orders for accounts that were never going to pay on time inflates the denominator with receivables that were "collectible" on paper only. Tightening limits for risky segments and reviewing terms improves CEI upstream, which is exactly what AI-assisted credit management is designed to do without slowing sales down.
3. Reactive, not proactive, outreach
Most teams only contact a customer once an invoice is past due. By then the customer's AP run has already happened. Pre-due reminders, sent a few days before the due date, prevent the delinquency rather than chasing it.
4. Wrong contact, wrong channel
According to Versapay, 86% of business and finance leaders still rely on email and phone to communicate with customers about invoices, channels where context gets lost and the person responsible for payment is often not looped in. In many LatAm markets, WhatsApp is where AP contacts actually respond.
5. Collector capacity
When one collector owns 400 accounts, they work the biggest balances and the loudest customers. The long tail of mid-size overdue invoices never gets touched, and CEI quietly erodes month after month.
How to improve your Collection Effectiveness Index
Every lever below either grows the numerator (collect more) or cleans up the denominator (stop creating uncollectible receivables). The highest-impact ones share a theme: reach every collectible account, before it's late, on the channel the customer uses.
Automate pre-due and past-due reminders
The single fastest CEI win is coverage. Automated, personalized reminders at day −3, day +1, day +7 and day +15 mean no invoice falls through the cracks because a collector was busy. If you're still building the cadence, start with this guide to automated payment reminders.
Put an AI agent on the long tail
This is where AI collections agents change the math. A conversational AI agent like Darwin AI's Rio can contact every account with an open invoice over WhatsApp, email or voice, confirm the right payer, resolve simple disputes ("send me the invoice again", "the PO number is wrong"), and capture a promise to pay, then hand anything complex to a human collector with full context. Your collectors stop being dialers and start being negotiators, and the long tail that was quietly dragging CEI down gets worked every single day.
Convert promises into payments
A promise to pay only helps CEI if the money actually arrives inside the period. Confirm the date, send a payment link, and follow up the morning of. The promise-to-pay kept-rate guide walks through how to close that gap.
Offer more ways to pay
Every extra step between "I'll pay" and "paid" costs you collectible cash. Cards, ACH or local transfer, and pay-by-link inside the reminder itself remove friction at the moment of intent.
Fix invoice accuracy upstream
Validate PO numbers, tax IDs and delivery confirmations before the invoice leaves the building. Every dispute you prevent is a receivable that stays collectible, and every day you shave off cash application means the payment shows up in this period's numerator instead of next month's.
Segment and prioritize
Not every overdue account deserves the same effort. Score accounts by balance, days late and payment history, then let humans work the high-value, high-risk segment while automation covers the rest. Prioritization is how a five-person team produces the CEI of a fifteen-person team.
Push your CEI past 90% without adding collectors
Rio, Darwin AI's collections agent, reaches every open invoice on WhatsApp, email and voice, and hands your team only the conversations that need a human.
Meet RioFAQ
What does the Collection Effectiveness Index measure?
CEI measures the percentage of receivables that were collectible in a period and were actually collected. It isolates collections execution from sales volume and payment terms.
What is a good Collection Effectiveness Index?
Benchmarks vary slightly by source: Versapay treats 80% or above as good, while HighRadius uses 85% or higher. Best-in-class teams operate above 90%.
How is CEI different from DSO?
DSO measures how many days it takes to collect (speed). CEI measures what share of collectible receivables you collected (quality). Higher is better for CEI; lower is better for DSO.
How often should I calculate CEI?
Monthly is standard for operational tracking, with a quarterly view to smooth out one-off swings. Always use the same period for every input in the formula.
Can AI improve CEI?
Yes. AI collections agents raise CEI mainly by increasing coverage: every open invoice gets a timely, personalized contact on the customer's preferred channel, and humans focus on the accounts that need negotiation.
