Company Action Level sits at 2.0 times Authorized Control Level RBC, Regulatory Action Level at 1.5, Mandatory Control Level at 0.70, and the trend test reaches up to 3.0 (NAIC Model #312, Section 1). The denominator behind every one of those multiples is built from a square root, so on a stylised life balance sheet a 10-unit charge adds 5.00 units of ACL when it lands in C-0 and 0.50 when it lands in C-4b.
That spread is the part of the formula the headline ratio hides. The NAIC's Risk-Based Capital topic page describes the calculation in three lines, "adding up the main risks insurance companies commonly face," "considering potential dependencies among these risks," and "allowing for the benefits of diversification" (NAIC, June 2026). Thirty-nine pieces on this site have reported a factor change against that ratio; this is the reference showing the arithmetic each of them moves.
Key Takeaways
- Five squared terms sit under the life formula's root, (C-1o + C-3a), (C-1cs + C-3c), C-2, C-3b and C-4b, while C-0 and C-4a add outside it, so an affiliate charge or a premium-based business-risk charge is never diversified (NAIC Life RBC Instructions, LR031).
- 0.89 versus 0.14: on the stylised life sheet a unit of C-1o adds 0.89 of a unit to RBC after covariance because it shares the largest squared term, while a unit of C-3b health credit risk adds 0.14, so a 10-unit move takes a 400% company to 361% or to 393%.
- 3% of RBC after covariance is the Basic Operational Risk add-on in both formulas, and the life version is offset by C-4a, so on the stylised life sheet it nets to zero while the P&C sheet carries the full 2.52 units.
- 338% against 354%: a 20-unit reserve strengthening that adds 5 units to R4 pulls the stylised P&C company's ratio to 338%, sixteen points below the 354% a surplus-only reading would predict, because the strengthening raises the denominator while it cuts the numerator.
- 1.6% is the rise in industry-average life RBC after covariance that the Academy's proposed 50%, 25% and 50% cross-risk correlations would produce, the first time the structure would use anything between zero and full correlation (NAIC Life RBC Working Group, June 2025).
The Components: What Each Formula Charges, and Where the Root Starts
Risks in the life formula are named C-0 through C-4. C-0 is asset risk in affiliates and off-balance-sheet items. C-1 is asset risk on everything else, split into C-1o for bonds, mortgages and other fixed income and C-1cs for common stock. C-2 is insurance risk: mortality, morbidity and longevity. C-3 covers interest rate risk (C-3a), health credit risk (C-3b) and market risk on guarantees (C-3c). C-4 is business risk, with C-4a on premium and C-4b on health administrative expense.
The Life RBC Forecasting and Instructions combine them on page LR031 as C-0 + C-4a + the square root of [(C-1o + C-3a)² + (C-1cs + C-3c)² + (C-2)² + (C-3b)² + (C-4b)²]. The instructions state the assumption: "It is statistically assumed that the C-1o risk and a portion of the C-3 risk are correlated, while the C-1cs risk, the C-2 risk, the balance of the C-3 risk and a portion of the C-4 risk are independent of both" (NAIC, 2024 edition). Everything under the root gets diversification; everything outside it is treated as fully correlated with the rest.
The P&C formula runs R0 through R5 plus Rcat: R0 affiliated insurers, R1 fixed income, R2 equity, R3 credit including reinsurance recoverables, R4 loss and loss adjustment expense reserves, R5 net written premium, Rcat catastrophe. Page PR032 adds them as R0 + SQRT(R1² + R2² + R3² + R4² + R5² + Rcat²), with only R0 outside the root. Health RBC has the same shape, H0 outside and H1 asset, H2 underwriting, H3 credit and H4 business risk inside (NAIC Health RBC Instructions).
The topic page's line that "interest rate risk is included only in the life formula, while catastrophe risk is included only in the P/C formula" lands at a specific place in each structure. Interest rate risk enters as C-3a, squared with C-1o, so bond default and disintermediation charges amplify each other in one term. Catastrophe risk enters as its own squared term, and Rcat is itself a root: the 2026 instructions combine earthquake, hurricane and wildfire "by square root of sums of squares" (Foley & Lardner, April 2026). The working group adopted wildfire proposal 2025-20-CR on March 23, 2026 (NAIC Capital Adequacy Task Force, Spring 2026).
Nested roots collapse. Because Rcat² is the sum of the three peril charges squared, the outer formula is arithmetically identical to a root with eight independent terms, R1 through R5 plus earthquake, hurricane and wildfire, each squared on its own. Adding wildfire therefore adds a ninth squared term to the P&C denominator. This site's coverage of the wildfire addition to the binding Rcat formula reported that the factor moved little capital in aggregate, and the arithmetic is the reason: a peril charge that is small relative to R4 and R5 contributes almost nothing to the root.
Other 2026 changes covered on this site each map to one component. The mortgage loan factor cut from 1.75% to 0.68% and the collateral loan look-through, with factors from 10% to 90%, both act on C-1o, the component inside the largest life term. The draft AG 55 guidance asks cedents to recompute the whole ratio without a treaty, so it restores charges to C-1o and C-2 and removes reserve credit from total adjusted capital at the same time.
The Covariance Step: Why the Same Dollar Moves the Ratio Three Ways
The root's partial derivative with respect to any component is that component's term divided by the whole root, so the marginal effect of a dollar of charge equals the share of the root its term already carries. A large term absorbs new charges at nearly a dollar for a dollar; a small term absorbs them at a fraction. The table works this on two stylised balance sheets, with total adjusted capital fixed at four times the base ACL.
| Formula | Component (base charge) | Marginal RBC per unit of charge | ACL added by a 10-unit increase | Ratio after, from 400% |
|---|---|---|---|---|
| Life | C-0 affiliates (5) | 1.00 | 5.00 | 356.5% |
| Life | C-1o fixed income (50) | 0.89 | 4.43 | 361.0% |
| Life | C-3a interest rate (10) | 0.89 | 4.43 | 361.0% |
| Life | C-2 insurance (30) | 0.49 | 2.45 | 377.4% |
| Life | C-1cs common stock (15) | 0.28 | 1.42 | 386.6% |
| Life | C-3b health credit (5) | 0.14 | 0.72 | 393.1% |
| Life | C-4a business, premium (8) | 1.00 | 5.00 | 356.5% |
| Life | C-4b business, admin expense (2) | 0.10 | 0.50 | 395.1% |
| P&C | R0 affiliates (5) | 1.00 | 5.15 | 357.5% |
| P&C | R4 reserves (60) | 0.78 | 4.03 | 365.9% |
| P&C | R5 written premium (40) | 0.55 | 2.83 | 375.4% |
| P&C | Rcat catastrophe (25) | 0.37 | 1.91 | 383.1% |
| P&C | R2 equity (15) | 0.25 | 1.28 | 388.5% |
| P&C | R1 fixed income (10) | 0.19 | 0.97 | 391.3% |
| P&C | R3 credit (10) | 0.19 | 0.97 | 391.3% |
Computation: the life sheet is C-0 5, C-1o 50, C-1cs 15, C-2 30, C-3a 10, C-3b 5, C-3c 0, C-4a 8, C-4b 2. Its root is 68.95, RBC after covariance 81.95, gross operational risk 2.46 which the C-4a offset of 8 reduces to zero, ACL 40.97 and total adjusted capital 163.90. The P&C sheet is R0 5, R1 10, R2 15, R3 10, R4 60, R5 40, Rcat 25: root 79.06, RBC before operational risk 84.06, plus 3% gives 86.58, ACL 43.29 and total adjusted capital 173.16.
Each row raises one component by 10 and recomputes the chain under the LR031 and PR032 formulas. Marginal figures are averages over the 10-unit step, so they sit slightly below the point derivative for the largest terms. On the life sheet C-4a moves the ratio as hard as C-0 because the instructions place it outside the root, and the same 10 units cost 4.43 of ACL in C-1o and 0.72 in C-3b, a six-fold difference decided by which squared term each shares and how large that term already is.
Operational risk add-ons work differently across the two formulas. Both instructions apply "a risk factor of 3.00% to the amount reported" as RBC after covariance (NAIC Life RBC Instructions, LR031). In life, "a company's C-4a Post Tax reported on Line (65) is offset against operational risk," floored at zero, so a company whose premium-based business charge exceeds 3% of its covariance total pays nothing extra. P&C has no offset unless it owns life subsidiaries, so the stylised P&C company pays 2.52 units, and every P&C row above is grossed up by 3% on its way to ACL.
Total adjusted capital, the numerator, is wider than surplus for a life company. Model #312 defines it as statutory capital and surplus plus "such other items, if any, as the RBC instructions may provide" (NAIC Model #312, Section 1N). The life instructions add the asset valuation reserve at 100% and the dividend liability at 50%, and subtract the hedging fair value adjustment (LR033), because "availability of the AVR and voluntary investment reserves to absorb specific losses was not assumed" when the C-1 factors were set (NAIC, 2024 edition). A P&C writer's adjustment runs the other way, deducting non-tabular reserve discount from surplus.
Numerator and denominator move together on a reserve action. Take the stylised P&C company at 400% and strengthen reserves by 20 units, with an R4 factor that adds 5 units of charge. Total adjusted capital falls to 153.16, which alone would leave the ratio at 354%. R4 rises from 60 to 65, the root climbs from 79.06 to 82.86, and ACL rises from 43.29 to 45.28. The ratio lands at 338%, with the extra sixteen points coming from the denominator.
The AG 55 pre-reinsurance recalculation runs the same double movement in reverse, removing a treaty's reserve credit from the numerator and restoring its charges to the denominator in one step.
Action Levels, the Two Ratio Conventions, and the Assumption Under the Root
Model #312 defines four levels as multiples of ACL: Company Action Level is "the product of 2.0 and its Authorized Control Level RBC," Regulatory Action Level "the product of 1.5," Authorized Control Level "the number determined under the risk-based capital formula," and Mandatory Control Level "the product of .70" (NAIC Model #312, Section 1K). Below 200% the insurer files an RBC Plan; below 150% the commissioner may issue corrective orders; below 100% the commissioner may take control; below 70% the topic page says "a regulator is obligated to take over management."
Between 200% and 300% the trend test applies. A life or fraternal insurer whose total adjusted capital sits "between 2.0 and 3.0 times the Authorized Control Level" projects the larger of its latest one-year decline in margin and its three-year average decline, and "any company that trends below 1.9 times the Authorized Control Level Risk-Based Capital would trigger Company Action Level RBC regulatory action" (NAIC Life RBC Instructions, LR035). A P&C insurer in the same band is tested on its combined ratio under the P&C instructions. Above 300% the topic page says "no regulatory intervention is needed."
Two ratio conventions coexist, and they differ by a factor of two. The NAIC ratio is total adjusted capital over ACL "including Basic Operational Risk," the definition on the topic page and on page PR034 of the P&C instructions. Many 10-Ks and rating agency reports quote total adjusted capital over Company Action Level RBC, which is ACL times 2.0. A company at 400% of ACL is at 200% of CAL, and a company reported at 450% on the CAL basis is at 900% on the NAIC's. Every band in this article is on the ACL basis.
What the Square Root Assumes, and Who Is Recalibrating It
The covariance benefit is a convention with a stated basis: the risks under the root are either fully independent or, inside one term, fully correlated, with nothing between. Paul Navratil of the American Academy of Actuaries told the Life RBC Working Group that "the current structure has either zero or 100% correlation between all the risks, except for longevity and mortality risks" (NAIC Life RBC Working Group minutes, June 2025). His proposal, exposed as 2025-13-L, regroups the components into Credit, Equity, Interest Rate, Insurance and Business, then applies 50% correlation between credit and equity, 25% between credit and interest rate, and 50% between equity and interest rate.
The observed ranges are wide: zero to 75% for credit and equity, zero to 25% for credit and interest rate, 43% to 75% for equity and interest rate, with correlations rising in stress. For a hypothetical company matching the 2023 industry aggregate the change "will slightly increase the RBC after covariance (as a percentage of RBC before covariance) by 1.6%," with the largest impact for companies concentrated in C-1cs. The C-1o and C-3b pairing carries 25% "due to the lack of data and the conservative approach," a judgment rounded to the nearest 25% "to avoid any appearance of a false position."
The P&C side is recalibrating a different diversification layer at the same time. The Academy's November 2025 concentration factor report found the line-of-business diversification credit inside R4 and R5, capped today at 30%, indicated at 46% for premium and 66% for reserves, and "any of these alternatives implies an MDC higher than the current 30%" (American Academy of Actuaries, November 2025). The Task Force's Spring 2026 summary records the working group reviewing action levels "under the current formula compared to a formula incorporating the Academy's suggested 45% premium and 65% loss concentration factors."
Those two projects pull in opposite directions, more correlation on the life side and more diversification on the P&C side, and both set by convention a parameter that an internal economic capital model estimates from the company's own book. An internal model correlates a bond portfolio and a mortality block from that company's data at that company's confidence level; the RBC root correlates them at zero, for every company, at a safety level the 2026 governance framework is only now asking to be stated consistently across factors.
The same balance sheet therefore produces two ratios that respond to the same event by different amounts. A reserve strengthening that costs sixteen extra points of RBC ratio through the covariance term may cost an internal ratio far less, or far more, depending on a correlation the formula has fixed for everyone.