3.2 How Life Insurance Works: Mortality, Interest, Reserves
Key Takeaways
- Premiums are built from mortality, interest, and expense (MIE); gross premium equals the net premium plus expense loading.
- Higher mortality raises premiums while higher assumed interest lowers them; the two factors move in opposite directions.
- Mortality tables such as the Commissioners Standard Ordinary (CSO) table combine with the law of large numbers to make pooled deaths predictable.
- Level premiums overcharge in early years and undercharge later; this overcharge funds statutory reserves.
- Reserves are the insurer's liability to pay future claims and form the basis of a permanent policy's cash value, which term insurance generally lacks.
The Three Pricing Factors: Mortality, Interest, Expense (MIE)
Every life insurance premium is built from three components, remembered as MIE:
| Factor | Role in Pricing | Effect on Premium |
|---|---|---|
| Mortality | Expected death claims, from a mortality table | Higher mortality raises premium |
| Interest | Earnings the insurer assumes on invested premiums | Higher interest LOWERS premium |
| Expense | Operating costs, commissions, taxes (the 'loading') | Higher expense raises premium |
The net premium reflects only mortality and interest - the pure cost of providing the death benefit. Adding the expense loading produces the gross premium, the amount the policyowner actually pays.
Gross Premium = Net Premium + Expense Loading
Notice that mortality and interest move premiums in opposite directions. If people die sooner than expected (higher mortality), claims rise and premiums must rise. If the insurer earns more interest on the premiums it holds, it needs less premium up front, so premiums fall. This inverse relationship is a frequent exam point.
Mortality Tables and the Law of Large Numbers
Insurers cannot predict whether any one person will die this year, but they can predict the rate of death across a large pool. The law of large numbers holds that as the number of similar exposure units increases, actual results converge on the statistical expectation. Pool enough lives and the death rate becomes reliably predictable.
That predicted rate comes from a mortality table, which states the number of deaths expected per 1,000 lives at each age. The current standard is the Commissioners Standard Ordinary (CSO) table, used for reserve and nonforfeiture calculations. Mortality rises with age, so the pure cost of one year of coverage - the mortality charge - climbs every year.
Exam trap: The law of large numbers does not reduce risk for any individual; it makes the AVERAGE outcome predictable for the insurer. That predictability is what allows a level premium to be calculated in advance.
Why Level Premiums Create Reserves
If premiums simply tracked the annual mortality charge, they would start very low and become unaffordable in old age. To avoid that, permanent policies use a level premium: the same amount every year.
In the early years the level premium is far more than the true mortality cost - the policy is overcharged. In later years the level premium is less than the soaring mortality cost - the policy is undercharged. The early overcharge does not vanish; the insurer invests it.
| Period | Level Premium vs. True Cost | Result |
|---|---|---|
| Early years | Premium exceeds mortality cost | Builds up a fund |
| Later years | Premium below mortality cost | Fund subsidizes the shortfall |
This accumulated overcharge becomes the reserve.
Reserves and Cash Value
The reserve is a liability on the insurer's books - money set aside to guarantee the insurer can pay future claims. State law dictates a minimum statutory reserve computed with the CSO table and an assumed interest rate, so regulators can verify solvency.
The policyowner's interest in that fund is the cash value. As the reserve grows, so does the guaranteed cash value, which the owner can access through loans, withdrawals, or surrender.
Permanent vs. Term
- Permanent policies (whole life, universal life) use level premiums, accumulate reserves, and therefore build cash value.
- Term insurance charges a premium close to the rising annual mortality cost (or a short-period level premium) and builds little or no cash value - it is pure protection.
Net Amount at Risk
The insurer's true exposure is the net amount at risk:
Net Amount at Risk = Death Benefit - Cash Value
As the reserve and cash value grow, the net amount at risk shrinks, reaching zero at the policy's endowment age (100 or 121), when cash value equals the face amount.
All else equal, if an insurer assumes a HIGHER rate of interest earnings on the premiums it holds, the effect on the premium charged is that the premium will:
The statutory reserve held by a life insurer primarily represents:
Putting the Premium Together: A Worked Build-Up
Tracing a premium from net to gross cements the MIE relationship.
Step 1 Mortality cost (from CSO table) $4.20 per $1,000
Step 2 Less interest discount (assumed 3%) ($0.90)
= Net premium $3.30 per $1,000
Step 3 Plus expense loading (commissions, $1.20
admin, taxes)
= Gross premium $4.50 per $1,000
On a $100,000 policy that is $450 per year ($4.50 x 100 units of $1,000). Notice how raising the assumed interest rate would enlarge the interest discount, shrinking the net - and therefore the gross - premium. Raising mortality or expenses pushes the gross premium up.
| Component | Direction premium moves when this rises |
|---|---|
| Mortality | Up |
| Interest (earnings) | Down |
| Expense | Up |
Exam trap: Gross premium = net premium PLUS expense loading. The net premium reflects only mortality and interest; expenses are added last. If a question asks what distinguishes net from gross, the answer is the expense loading.