How insurers make money from underwriting and investments
Key metrics: loss ratio, expense ratio, combined ratio, and underwriting margin
How reserves, float, and reinsurance affect profitability and risk
Life vs. property & casualty (P&C) metrics: persistency, VNB, reserve development
How to calculate earned premiums, combined ratio, and reserve coverage step-by-step
How to spot underwriting cycles, pricing power, and risk-based capital signals
Practical ways to compare insurers and avoid common pitfalls
Concept explanation
Insurance companies sell promises. Policyholders pay premiums today, and insurers may pay claims in the future. This timing gap creates two profit streams: underwriting profit or loss from the insurance business itself, and investment income on the money held before claims are paid. The key to analyzing insurers is understanding how these streams interact over time.
Underwriting revolves around three ingredients: premiums, claims, and expenses. Premiums are the price of insurance coverage. Claims (or losses) are what the insurer pays out when events occur. Expenses include acquisition costs (commissions, marketing), administrative costs, and taxes. Because claims often occur long after premiums are collected, insurers set aside reserves to cover expected future payouts.
Investment income comes from investing the float—the pool of funds generated by premiums received but not yet paid out as claims or expenses. Insurers typically invest in bonds to match expected claim payments. The quality, duration, and yield of this portfolio influence results significantly, especially in low or rising interest rate environments.
Finally, reinsurance allows insurers to transfer part of their risk to other insurers. It helps smooth results, protect capital during catastrophes, and manage growth. But it also reduces net premiums and can hide underlying risk selection if not analyzed carefully.
Why it matters
Insurers’ accounting can feel counterintuitive compared to typical businesses. Revenue recognition is unique: premiums are recognized as earned over the coverage period, not all at once. Claims may be estimated years in advance, making reserve adequacy a pivotal factor. Small assumption changes can materially shift reported profits.
For investors, this means headline earnings can be noisy. A 95% combined ratio can mask weak reserve practices, while a 102% combined ratio might still be acceptable if investment income is strong and reserves are conservative. Context matters: product mix, underwriting cycle, catastrophe exposure, and reinvestment yields all shape sustainable returns on equity.
The sector also bifurcates: P&C insurers focus on short- to medium-tail risks like auto or homeowners, while life insurers focus on long-duration liabilities like annuities and protection products. Each requires different metrics and risk lenses. Understanding these differences helps you compare insurers appropriately and avoid apples-to-oranges mistakes.
Calculation method
Below are core insurance metrics and how to compute them.
Premiums: written vs. earned
Written premium: the total premium of policies issued in the period
Earned premium: the portion of written premium that relates to the time already elapsed on the policies
Example: A 12-month policy with 1,200writtenonJan1earns100 per month. After 3 months, earned premium is 300;unearnedis900.
Earned Premium = Written Premium - Change in Unearned Premium
Loss ratio
Measures claims cost relative to earned premium.
Loss Ratio = Incurred Losses / Earned Premium
Incurred losses include paid claims plus change in loss reserves.
Example: Earned premium 1,000;incurredlosses650 ⇒ Loss Ratio = 65%.
Expense ratio
Measures underwriting expenses relative to earned premium.
Expense Ratio = Underwriting Expenses / Earned Premium
Underwriting expenses include acquisition (commissions), general and administrative, and premium taxes.
Example: Underwriting expenses 320;earnedpremium1,000 ⇒ Expense Ratio = 32%.
Combined ratio
Sum of loss and expense ratios. Below 100% indicates underwriting profit before investment income.
Combined Ratio = Loss Ratio + Expense Ratio
Example: 65% + 32% = 97% combined ratio.
Underwriting margin (pre-investment):
Underwriting Margin = 1 - (Combined Ratio)
In the example: 1 - 0.97 = 3%.
Reserve coverage and development (P&C)
Loss reserves: estimate of future claim payments for events already occurred
Reserve coverage ratio:
Reserve Coverage = Loss Reserves / Net Paid Losses (or / Net Claims)
Reserve development: change in prior-year reserves after actual claims emerge
Reserve Development = Prior Accident Year Reserves - Actual Losses for That Year
Positive development (release) boosts earnings; adverse development reduces earnings.
Float and investment yield
Float approximates funds available to invest that are financed by policyholders.
Float ≈ Unearned Premiums + Loss Reserves + Other Insurance Liabilities - Related Receivables
Portfolio yield measures investment income efficiency.
Investment Yield = Net Investment Income / Invested Assets
Risk-based capital (RBC) and solvency
RBC ratio indicates capital adequacy relative to risk profile.
RBC Ratio = Total Adjusted Capital / Authorized Control Level RBC
Common thresholds: regulators watch closely as ratios approach intervention levels. Many high-quality insurers target RBC well above 300%.
Life insurance specifics: persistency, APE, and VNB
Persistency: percentage of policies remaining in force after a period; 1 - surrender rate
Persistency Rate = 1 - Surrender Rate
APE (Annualized Premium Equivalent) standardizes new business volume.
APE = Annualized Regular Premium + 10% × Single Premium
VNB / VNB margin reflects the present value of expected future profits from new business.
VNB Margin = VNB / APE
Higher persistency and positive experience variances (mortality, morbidity, expenses) typically lift VNB.
Tip: Always reconcile net vs. gross measures. Use net premiums and net losses (after reinsurance) for net ratios; use gross if analyzing pre-reinsurance performance.
Case study
Assume a mid-sized P&C insurer with the following for the year:
Gross written premium (GWP): $5,000m
Ceded written premium (reinsurance): 1,000m⇒Netwrittenpremium(NWP):4,000m
Net investment income: 420m;averageinvestedassets:12,000m
Investment Yield = 420 / 12,000 = 3.5%
Float estimate: unearned premiums 1,600m;lossreserves5,000m; other liabilities 200m;receivables600m
Float ≈ 1,600 + 5,000 + 200 - 600 = 6,200m
Prior-year reserves were 4,800m;actuallossesonthatyearwere4,950m
Reserve Development = 4,800 - 4,950 = -150m (adverse)
Interpretation:
Strong underwriting: a 93.4% combined ratio implies core discipline
Investment tailwind is moderate with 3.5% yield on a large float
Adverse reserve development of $150m is a yellow flag—dig into which lines drove it (e.g., commercial auto, liability)
Reinsurance use is material (20% of GWP); assess cost vs. protection during catastrophes
Practical applications
Screening and comparison
Prefer insurers with multi-year average combined ratios below 100% and low volatility across cycles
Check reserve development over 5-10 years: frequent adverse development suggests weak pricing or optimistic reserving
Evaluate RBC ratio and trends. Healthy buffers reduce downside risk and support dividends/buybacks
Compare investment portfolio duration and credit quality to liability profile. Mismatch risk can bite when rates move
Cycle awareness
P&C pricing is cyclical. Tight capacity after large catastrophes often leads to rate hardening and better combined ratios
Track management commentary on rate increases, exposure growth, and loss cost inflation. If pricing outpaces loss trends, margins expand
Reinsurance strategy
High ceded ratios can stabilize results but also mask weak underwriting if terms are expensive
Review catastrophe covers, retention levels, and reinstatement terms. A cheap combined ratio obtained by ceding too much may depress long-run ROE
Life insurance focus
Monitor persistency: rising surrenders may reflect product mispricing or rate-sensitive lapses
Track VNB and VNB margin by product. Shifts toward capital-light, fee-based products (e.g., asset management, protection) can lift returns
Assess assumptions: mortality, morbidity, expenses, and discount rates. Experience gains should be recurring, not one-off
Investment income and rates
In rising rate environments, new money yields can lift future investment income even if current yields lag
Beware unrealized losses in bond portfolios under fair value accounting. Understand capital impacts and asset-liability duration matching
Valuation shortcuts
P&C: Price-to-book alongside sustainable ROE and combined ratio history. Strong franchises often command P/B premiums
Life: Embedded Value and VNB multiples where disclosed. Cross-check with P/B and return profile
Look for consistent underwriting profitability first. Investment income should be the bonus, not the crutch.
Common misconceptions
よくある誤解
- A combined ratio under 100% always means great performance. It can be flattered by prior-year reserve releases or heavy reinsurance without sustainable pricing power.
- Investment income can fix bad underwriting. Over time, weak underwriting erodes capital and raises reinsurance costs, offsetting portfolio yields.
- All premium growth is good. Rapid growth in soft markets often means underpriced risk and future adverse development.
- High RBC ratio guarantees safety. Capital strength is necessary but not sufficient—asset quality, catastrophe exposure, and reserving discipline matter.
- Life and P&C insurers are analyzed the same way. Life needs focus on persistency, assumption changes, and VNB; P&C leans on combined ratio and reserve development.
Summary
まとめ
- Insurers earn from underwriting and investing float; both need analysis in context.
- Core ratios: loss, expense, and combined ratios reveal underwriting discipline.
- Reserves and their development are critical to assessing true profitability.
- Float size and investment yield drive steady income but must match liabilities.
- RBC and solvency metrics show capital adequacy; watch trends, not just levels.
- Life analysis emphasizes persistency, APE/VNB, and assumption changes.
- Compare multi-year results across cycles to avoid being fooled by one-offs.
Glossary
Written Premium: Total premium from policies issued during a period, before earning over time.
Earned Premium: Portion of written premium recognized as revenue for coverage already provided.
Loss Ratio: Incurred losses divided by earned premium; measures claims cost.
Expense Ratio: Underwriting expenses divided by earned premium.
Combined Ratio: Loss ratio plus expense ratio; under 100% indicates underwriting profit.
Reserves: Liabilities set aside for future claim payments on events already occurred.
Reserve Development: Adjustments to prior-year reserves as actual claims emerge.
Float: Funds held between collecting premiums and paying claims, available to invest.
RBC Ratio: Risk-based capital ratio measuring capital relative to risk.
Persistency: Percentage of policies that remain in force over time (life insurance).
APE: Annualized Premium Equivalent; a standard measure of new business volume.
VNB: Value of New Business; present value of expected profits from new policies.
