Experience Mod Calculator — Workers' Comp X-Mod and What Each Claim Costs

What is your workers' comp experience mod, and which claims are costing you?

Type the values from your experience rating worksheet and list your claims. You get an estimate of your experience mod, the premium it adds or saves, and what each claim costs you per year and over the three years it stays in the calculation, plus what one more claim would do. Useful before you bid work that asks for a mod under 1.00, and before you decide whether to fight a claim.

Calculated in this browser tab. No account, no upload. The example is made up. A planning estimate, not your bureau's mod.

1. Your rating worksheet

These come from your bureau's worksheet (or your broker). They change by state, payroll and year, so none are assumed.

Expected losses, E ($)

D-ratio (0 to 1)

Weighting value, W (0 to 1)

Ballast, B ($)

Annual manual premium ($, optional)

Split point ($)

Per-claim accident limit ($)

Medical-only discount (ERA)

2. Your claims

One per line: policy year, medical-only or indemnity, total incurred.

Claims

Defaults for the split point and claim limit are example values; use your state's figures.

Enter your worksheet values and claims, or load the example, then click Estimate my mod.

Result

What each claim costs you

Year	Type	Incurred	Counted	Mod without it	Mod points	Per year	Over 3 years

If one more indemnity claim lands

Claim size	New mod	Extra premium per year

The rules this applies, and what it leaves out

NCCI-style formula: mod = (Ap + W·Ae + (1−W)·Ee + B) / (E + B). Primary losses are each claim's first dollars up to the split point; the rest is excess, weighted down by W.
Each claim is capped at the per-claim accident limit, and medical-only claims can be counted at a discount (ERA) where your state allows it.
Not modelled: independent-bureau plans (California, New York, Pennsylvania, New Jersey, Michigan and others), the exact W and B tables, expected loss rates, ownership changes, subrogation and claim valuation dates. The mod you pay is the one on your bureau's worksheet.

Common questions

What is an experience modification factor?

A multiplier, usually near 1.00, that your workers' compensation rating bureau applies to your manual premium. It compares your own claims over roughly three policy years with what is expected for businesses of your size and class. Below 1.00 is a credit; above 1.00 is a debit.

How is the experience mod calculated?

In NCCI states: mod = (Ap + W x Ae + (1 - W) x Ee + B) / (E + B), where Ap and Ae are your actual primary and excess losses, Ee the expected excess losses, E the total expected losses, W the weighting value and B the ballast. Primary losses are the first slice of each claim up to the split point. This tool applies that formula to the values you type from your worksheet.

Does one big claim or several small ones hurt more?

Primary losses count at full weight, and each claim's first dollars up to the split point are primary, so frequency hurts. Excess dollars are weighted down by W, so a single large claim is partly cushioned. Several claims of a few thousand dollars can cost more in mod than one larger claim.

How long does a claim stay in my mod?

Normally three policy years, excluding the most recent year. This tool shows what each claim costs per year and over three years if you enter your manual premium.

Does this work in California, New York, Pennsylvania or other independent-bureau states?

Those states use their own rating plans and formulas. This tool is NCCI-style arithmetic: use it for a rough picture there, and rely on your bureau's worksheet.

Is my data uploaded?

No. Everything runs in your browser tab and nothing is sent anywhere. There are no accounts.

Is this insurance, legal or financial advice?

No. It is a planning estimate from numbers you enter. The mod you are charged is set by your rating bureau. It does not file, dispute or change anything.