Incurred but not reported claims are the biggest number you cannot look up. This lesson explains what IBNR is and how it is estimated.
The claims lag creates a hole in the books: care has been delivered that no paid claim reflects yet. IBNR, incurred but not reported, is the estimate that fills the hole. It is one of the largest liabilities on a risk-bearing organization’s balance sheet and one of the least intuitive.
What IBNR is
IBNR is the estimated cost of care that has been incurred (the service happened) but not reported (no claim has been paid, and often none submitted yet). It is a liability: money the organization already owes, even though no invoice has landed. Add paid claims to IBNR and you get the true estimated cost of a period, called incurred claims:
Incurred claims = paid claims + IBNR
How it is estimated
You cannot look IBNR up; you estimate it, and actuaries do this with historical claim-payment patterns. The core idea is the completion factor: from past experience, you know roughly what fraction of a month’s claims are typically paid by a given number of months later. If two months after service you have historically seen 60 percent of claims, and you have $6 million paid so far, you estimate total incurred at $10 million and set IBNR at $4 million.
| Item | Amount |
|---|---|
| Paid claims so far | $6 million |
| Estimated completion | 60 percent |
| Estimated incurred (6M / 0.60) | $10 million |
| IBNR (incurred minus paid) | $4 million |
Recent months are the least complete and therefore the most uncertain, which is why IBNR for the latest period is the hardest to pin down.
Worth remembering: IBNR is an estimate, and estimates can be wrong. Under-reserve for IBNR and an organization looks profitable right up until the claims arrive and erase the margin. Many risk-bearing organizations have been surprised not by bad care management but by bad IBNR estimates.
Why non-actuaries need to understand it
A practice leader reading a “we are under budget” report should immediately ask: is that paid claims or incurred claims? Under budget on paid claims is meaningless if IBNR has not been added. IBNR is the difference between a number that looks good and a number that is true.
Key takeaways
- IBNR estimates the cost of care already delivered but not yet reported or paid.
- Incurred claims equal paid claims plus IBNR; that total, not paid claims, is the real cost.
- IBNR is estimated from historical completion patterns and is most uncertain for recent months, so under-reserving is a classic and dangerous error.
Check your understanding
What does IBNR represent?
IBNR (incurred but not reported) is the actuarial estimate of liabilities for care that has happened but whose claims have not yet arrived, filling the gap the claims lag creates.