The Experience Modification Rate (EMR), Explained

Every employer paying workers' compensation premium runs into this number sooner or later: the experience modification rate, or "mod." It's the single figure a rating bureau applies to manual insurance rates to raise or lower one employer's premium based on that employer's own claim history. This guide covers what NCCI's own explanation says the mod does, where its inputs come from, and why the calculators on this site don't produce one.

What experience rating does

NCCI's own guide to the Plan puts it in one sentence: "The differences are reflected by an experience rating modification (mod), based on individual payroll and loss records, which may result in an increase, decrease, or no change in premium." Rather than charging every employer in a classification the same average rate, the mod compares one employer's own payroll and claims against similarly classified employers and adjusts that employer's premium up, down, or not at all. NCCI names the two outcomes credit and debit: "an employer with better-than-average loss experience receives a credit, while an employer with worse-than-average experience carries a debit mod."

The experience period

The mod isn't built from a single year. NCCI's document sets the general span: "The experience period is generally based on three years of payroll and loss data but could range from containing less than 12 months of data up to the inclusion of 45 months of data." Data from a policy counts toward that period only if its effective date falls between 21 and 57 months before the mod's rating effective date, which keeps the most recent year's claims — still being valued by the insurance provider — out of the calculation until the following renewal.

Split rating: primary loss and excess loss

A mod doesn't treat every dollar of loss the same way. NCCI's document splits each ratable loss at a state-approved split point: "The amount of any ratable individual loss up to the split point is known as primary loss, which reflects frequency". Above that point, "The amount in excess of the split point is known as excess loss, which reflects severity". Primary losses carry more weight in the formula than excess losses do, so an employer with several small losses gets a larger mod adjustment than one with a single large loss of the same total dollar amount, even though both employers paid out the same amount in claims.

Ballast: a stabilizing factor, not a public formula

The mod formula also includes what NCCI's document calls the ballast factor. In its own words, ballast is "something that gives stability, such as heavy material in the hold of a ship to keep it from shifting too far one way or the other." NCCI's document adds that "the ballast factor in the experience rating formula helps prevent the mod from shifting too far above or below unity." Beyond that description, and the note that the ballast value grows as an employer's expected losses grow, NCCI's document doesn't spell out the ballast figure itself — that number lives on the rating worksheet, not in this explanatory guide.

Why this site doesn't calculate a mod

A mod is built from an employer's own filed payroll and claim history, reported by the insurance provider to the rating bureau — not from anything on an OSHA 300 Log or 300A summary. This site's calculators work only from OSHA recordkeeping data, so there's nothing in them to compute a mod from. See what the tools don't model for the rest of what's out of scope here.

What to ask your carrier or rating bureau for

Ask your insurance provider for your NCCI Experience Rating Worksheet, which shows your rating effective date, your classification codes, and whether the mod's status is preliminary, final or contingent — a preliminary mod is calculated with prior rating values and gets revised once the state's final values are in. If your company changed ownership, ask whether that change has been reported with an ERM-14 form, since NCCI may revise past mods when ownership changes. And check which organization actually computes your mod. NCCI develops it in the 39 jurisdictions that use the Plan, but North Carolina, Indiana and Massachusetts each have an independent rating organization that produces its own intrastate mod even though the Plan applies there — North Carolina's is the Rate Bureau. Minnesota and Wisconsin's independent organizations only combine with Plan states for interstate cases, so Minnesota's Workers' Compensation Insurers Association is the one to ask about a purely in-state claim. California doesn't use the Plan at all; its own Workers' Compensation Insurance Rating Bureau sets the rules there instead.

How a mod differs from TRIR

The TRIR calculator counts how often a recordable injury happened, scaled to 100 full-time workers over one year — a frequency count with no dollar amount anywhere in it. A mod starts from the opposite end: three years of an employer's actual payroll and claim dollars, split into primary and excess loss and weighed against similarly classified employers, ending in a single multiplier applied to premium. TRIR moves the moment one more case is added to the log; a mod moves only when a claim's cost, or the payroll behind it, shifts the years-long trend NCCI or the state's bureau is measuring. A single severe claim can leave TRIR untouched — one case is one case — while doing much more to the mod, because the mod weighs cost as well as frequency.