The reserve is money, not a note
When a claim is notified the insurer becomes liable for something whose amount
is unknown. Accounting does not permit waiting: the liability exists now, so an
estimate of it — the case reserve — is recognised now, and it flows straight
into the reported result for the period.
That single fact explains most of the machinery. The number is not an internal
guess an adjuster keeps in a notebook; it is a figure that moves the company's
profit, appears in regulatory returns, and will be examined. A system that
treats it as an editable field on a claim record has misunderstood what it is.
The vocabulary that follows is worth being precise about, because these three
are constantly conflated:
- Paid — money that has left.
- Case reserve — the estimate of what remains to be paid on this known
claim.
- Incurred — paid plus reserve, the current best view of the claim's total
cost.
Incurred is the number people mean when they say what a claim "cost", and it
changes every time either component does.
The first number is a placeholder, deliberately
At first notification almost nothing is known. Practice is to set an initial
reserve from an average — a formula reserve based on claim type, or a standard
opening figure by peril — and to replace it as soon as a human has looked.
That is not sloppiness, it is the least-wrong option. A zero reserve understates
the liability and produces a step change later; a speculative large number
distorts the period it lands in. An average by claim type is defensible, is
consistent across the book, and is expected to move.
What matters for the design is that the transition from formula to
adjuster-assessed is itself an event worth recording, because a reserve that
moved because someone finally read the file is a different thing from one that
moved because the claim got worse.
Every movement is an event
The reserve is not a value, it is a series. The current figure is derived from
the movements, and the movements are what get reported.
Claim CL-8841, motor, third-party injury
date movement case reserve paid incurred reason
2026-02-14 initial formula 3,500.00 0.00 3,500.00 FNOL, average by type
2026-03-02 adjuster estimate 12,000.00 0.00 12,000.00 medical report received
2026-05-19 payment 8,000.00 4,000.00 12,000.00 interim payment
2026-09-30 strengthening 26,000.00 4,000.00 30,000.00 liability admitted, PSLA revised
2027-01-08 settlement 0.00 29,500.00 29,500.00 closed, settled below reserve
Read the fourth row: the reserve rose by 18,000 in one movement, which is a
number that appears in that period's result and will be asked about. Read the
third: a payment of 4,000 reduced the reserve by 4,000 and left incurred
unchanged, because paying out of a reserve is not a new cost — it is the
liability converting into cash. Candidates who model a payment as reducing only
the reserve, or as increasing only paid, get incurred wrong in one direction or
the other.
The reason to store movements rather than a current value is that actuaries
need to see cost by accident period and development period — how a cohort of
claims from one period developed over subsequent periods — and that is
reconstructible from a movement history and impossible from a mutable field.
Indemnity and expense are separate
A claim costs two different kinds of money. Indemnity is what is paid to
settle the loss itself. Expense is what it cost to handle it: loss
adjusters, legal fees, engineers, surveyors.
They are reserved and reported separately because they behave differently and
are managed by different levers. A long liability claim can run up substantial
legal expense while indemnity stays flat; reinsurance treaties often treat them
differently; and expense ratios are a management metric in their own right.
Collapsing both into one number destroys information nobody can recover later.
IBNR covers what the case reserves cannot
Case reserves only exist for claims the insurer knows about. Claims have
occurred that have not yet been reported — the accident happened, the insured
has not called — and on some lines the delay is years.
IBNR is a bulk reserve for that gap, set by actuaries across a whole cohort
rather than per claim. It is worth understanding as a different object with a
different owner: an adjuster sets a case reserve on a file, an actuary sets IBNR
on a book, and an engineer's job is to feed the second with clean movement data
rather than to compute it.
The related consequence is that "total reserves" is case plus IBNR, and a report
that sums only case reserves understates the liability on any line with a
reporting delay.
Closed is not final
A claim can reopen — an injury worsens, a new party joins a suit, a recovery
arrives — and reopening restores a reserve on a file that had been closed at
zero.
Two design consequences follow. Closed claims cannot be archived into somewhere
expensive to write to, because reopening is a normal event rather than an
exception. And the reserve movement history has to survive closure, since the
reopened file's development is part of the same claim's story and an actuary
looking at development will want both.
The blunt version of the same point: on a long-tail line, an insurer does not
know what a year cost for a decade, and every number before then is an estimate
with a history attached.
The reserve is recognised money set against something nobody has measured yet.
Model the movements, not the value, because the movements are what the
business, the actuary and the regulator all actually read.
© 2026 Preptima. Originally published at preptima.com (opens in a new tab).