Guides
Work the Business Interruption Coinsurance Formula Yourself, Step by Step
Run the business interruption coinsurance formula yourself: the percentage, the required limit, the adequacy ratio, the payroll and indemnity inputs, a dollar example, and when to act.
What to take away
- The metric is the coinsurance adequacy ratiolimit carried divided by the limit required.
- A ratio under 1.00 turns every partial loss into a partial payment.
- Ordinary payroll and the extended period of indemnity raise the required limit, so leaving them out flatters the ratio.
- The ratio tests the limit, not the coverage, and cannot say whether a loss qualifies.
- Act below 1.10, and treat a ratio under 1.00 as a standing deduction from every partial loss.
The coinsurance percentage and the required limit
The business interruption coinsurance formula has three parts: the percentage, the values and the limit. The business income coverage form in ISO's CP 00 30 follows the same logic as property coinsurance. The insurer wants a limit equal to a chosen share of the values at risk over twelve months.
Coinsurance Percentages and Required Limit
- 50, 60, 70, 80, 90, 100coinsurance percentage options
- 12 monthsbusiness income values after loss
- Required limit = percentage × values + payroll
The percentage you chose appears on your declarations page. The policy states which percentages it allows, so use the one printed on your declarations rather than an assumed one. A lower percentage lowers the required limit and usually the premium, but it also narrows the margin before a penalty applies.
The required limit is the coinsurance percentage times the business income values for the twelve months after a loss. Add ordinary payroll only where the policy covers it. Divide the limit you bought by the required limit to get the coinsurance adequacy ratio.
Two options change the test. An agreed value option, an optional coverage in the same form, suspends the coinsurance condition when the insurer accepts a signed worksheet. Ask whether your policy carries it. Without it, the arithmetic below applies.
Work the formula in six steps
- Read the coinsurance percentage from your declarations page. It is the share of twelve-month business income values the policy requires you to carry.
- Build the twelve-month business income values. Business income is net income plus continuing normal operating expenses, including ordinary payroll only where the policy covers it. Take the figures from your annual income statement and a twelve-month projection, and list each line separately. Extra expense sits outside this calculation and has its own limit.
- Multiply the values by the coinsurance percentage. The result is the required limit.
- Read the business income limit you bought from the declarations page.
- Divide the limit bought by the required limit. The quotient is the adequacy ratio. A ratio of 1.00 or higher means no penalty applies.
- For a partial loss, multiply the loss by the ratio, subtract any deductible, and cap the result at the limit bought.
How to read the ratio
Effect on a partial loss
- 1.10 or higher
- No penalty, with room for growth
- 1.00 to 1.09
- No penalty today, thin against inflation
- 0.90 to 0.99
- Small penalty on every claim
- Below 0.90
- Penalty larger than most owners expect
Move to make
- 1.10 or higher
- Review at renewal
- 1.00 to 1.09
- Re-run the worksheet
- 0.90 to 0.99
- Raise the limit or choose a lower coinsurance percentage
- Below 0.90
- Decide before renewal
Read the table downward, not across. Any business income worksheet starts with three inputs: the coinsurance percentage, the payroll election and the period of indemnity. A commercial property requirements read covers which values the form expects before this arithmetic matters.
To get a worksheet and your values, ask the insurer or the carrier's online portal for the business income worksheet and the declarations page. An agent is not required for that request.
Ordinary payroll and the extended period of indemnity
Ordinary payroll is the biggest swing item. Under the ISO business income form, payroll is covered unless the policy carries the Ordinary Payroll Limitation or Exclusion endorsement, CP 15 10, which can exclude payroll or limit it to a set number of days. Read your declarations to see which applies. Payroll for 365 days raises the values at risk and the required limit. Payroll for 90 or 180 days lowers them.
Payroll and Extended Indemnity Impact
Item
- Ordinary payroll 365 days
- Values climb, limit rises
- Ordinary payroll 90 or 180 days
- Required limit falls
- Extended period of indemnity
- Adds weeks of values
- Skipping extended period
- Required limit too low
Effect on Required Limit
- Ordinary payroll 365 days
- Ordinary payroll 90 or 180 days
- Extended period of indemnity
- Skipping extended period
The extended period of indemnity is the second swing item. It continues the loss after the period of restoration ends, while sales are still below normal. Those weeks carry their own values, and a worksheet that skips them produces a required limit that is too low.
The report/values endorsement, CP 15 15, changes how values are reported to the insurer and how premium is adjusted. It does not change whether the values matter.
Example: one worksheet run twice
This worksheet uses index points, with a required limit of 100 when payroll is included. In dollars, these are illustrative required limits: $500,000 with payroll, taken as given. The same worksheet with payroll stripped out shows a required limit of $310,000, or index 62. The example does not reproduce the worksheet arithmetic behind either figure.
An owner buys a $400,000 limit against the second worksheet and believes there is a comfortable cushion. Against the first worksheet, the ratio is $400,000 divided by $500,000, which is 0.80. On a $200,000 partial loss, the policy pays 0.80 of the loss, or $160,000, and the owner absorbs $40,000.
The ratio is measured against the values the policy requires, not the values a worksheet happens to show.
What the ratio cannot tell you
- The ratio rests on a forecast. The sales projection inside the worksheet decides the answer.
- It says nothing about coverage triggers, waiting periods or exclusions.
- It ignores extra expense, which carries its own limit and can be the larger figure after a loss.
A ransomware outage that halts production is a business income claim too. Cyber insurance examples show how those losses are characterized when the cause is a network rather than a fire.
Attribution and its limits
A ratio that moves from 1.15 to 0.95 in a single quarter has several possible causes: new sales, price inflation, a lost contract, or an error in the worksheet. The number alone cannot separate them.
Two checks help. Compare the sales line against the general ledger, and compare the payroll election against the endorsement on the declarations page. A commercial property mistakes list covers errors that sit quiet until a claim.
When to stop measuring and decide
Set the trigger at 1.10. Below it, re-run the worksheet with the payroll election and the extended period included, then either raise the limit or select a lower coinsurance percentage.
Once two reviews in a row move the ratio by less than 5 percent, stop re-running it. The worksheet will not tell you anything new until sales, payroll or the policy itself changes. Revisit at renewal, at least 60 days out.
File the worksheet and the election letter when you stop. A commercial property checklist helps keep claim records together, and an undocumented payroll election is hard to argue later.
