Experience Modification Rate for Contractors: How the Mod Is Built and What Moves It

A contractor's experience modification rate (EMR) is the multiplier applied to the subject premium on a contractor workers compensation insurance policy. It divides your actual losses over a three-year experience period by the losses expected for a contractor with your payroll in your class codes. At 1.0 the two match, and the expected-loss half of that comparison is where most contractors misread their own number.

Expected losses come from your reported payroll in each class code, run through a filed expected loss rate. So a payroll reallocation at audit moves the mod with no new claims. What follows covers how the formula is assembled, who qualifies for a mod at all, which policy years feed it, and which bureau runs the arithmetic.

How is an experience modification rate calculated?

An experience modification rate divides adjusted actual losses by adjusted expected losses over a three-year experience period. The filed rule states it as Total A over Total B, rounded to two decimals (Rule ID ER-FORM-EAB03). Each side splits into primary and excess losses. The excess is weighted, and a stabilizing value is added to both.

Most pages print the bare ratio and call it the formula, which is why the EMR rating construction firms put on a bid form rarely matches a hand calculation.

The formula's variables, defined

The filed rules name each variable:

• Ap and Ae: actual primary losses (each claim up to the state split point) and actual excess (the dollars above it).
• Ep and Ee: the same split applied to expected losses, divided by the D-ratio.
• W, the weighting value, decides how much of the excess counts. It rises with employer size.
• B, the ballast, plus the stabilizing value: dollars added to both sides to damp the swing.

NCCI's ABCs of Experience Rating works it through: primary losses of $88,100, excess of $75,640 at a W of 0.16, and expected excess of $115,498 carried at one minus that weighting. Add a $45,900 ballast and both sides land on a $142,918 stabilizing value. Total A of $243,120 over Total B of $242,971 rounds to 1.00.

What does a mod of 1.0 actually mean?

A mod of 1.0 means a contractor's actual losses matched the losses expected for its payroll and class codes. Below 1.0 is a credit mod that lowers workers compensation premium, and above 1.0 is a debit mod that raises it. A factor of exactly 1.00 is unity, and the manual assigns it in five situations:

• The risk is not eligible for experience rating.
• The risk lacks the minimum required data.
• The business is new with no data available for a mod.
• The risk qualifies and the calculation resolves to 1.00.
• Data could not be provided after an ownership change.

Where does the expected loss number on my worksheet come from?

Expected losses aren't an estimate of your losses. They are a payroll calculation: your reported wages in each class code, divided by 100, then multiplied by that code's filed expected loss rate. A D-ratio splits that figure into expected primary and expected excess losses.

NCCI's Colorado advisory loss cost filing effective January 1, 2026 rates plumbing class 5183 at an expected loss rate of 0.817 per $100 of payroll, with a D-ratio of 0.34. For a contractor reporting $20.4 million of payroll under that code, the bureau arithmetic runs this way:

• $20,400,000 divided by 100 = 204,000
• 204,000 times 0.817 = $166,668 of expected losses
• $166,668 times 0.34 = $56,667 of expected primary losses

Why a payroll reallocation moves your mod

The arithmetic asks what you paid the crews and under which code, so how NCCI assigns your class codes sets the denominator before anyone counts a claim. Move $1,000,000 into roofing class 5551, filed at 2.358, and the same wages generate $23,580 of expected losses instead of $8,170 with no new claim.

One sheet metal and roofing sub doing about $30 million a year watched a premium audit move roughly $1.4 million of field wages out of the roofing code. Its expected losses fell, the claims didn't change, and the next mod came back higher.

Expected loss rates are filed state by state and reset in each annual loss cost filing, so the denominator moves even when the operation does not. Rates also vary sharply by trade. That same Colorado filing puts roofing at 2.358 against 0.817 for plumbing. Electrical contractors rated on class code 5190 carry their own filed rate.

Why do two contractors with the same claims have different mods?

A contractor's experience mod is payroll-weighted, so two contractors in the same class code with identical actual losses get different mods when their payrolls differ. Higher payroll produces higher expected losses and a smaller ratio. NCCI has published exactly that point and cautioned against using mods to compare employers.

Kathy Antonello, NCCI's Chief Actuary at the time, put it plainly in an NCCI Insights article published September 5, 2017. "It's not appropriate to use E-mods to compare the relative safety of employers." Her example takes two identical contractors in the same class code, each with $200,000 of actual losses. The one paying 20% higher wages, $12 million of payroll against $10 million, comes out at 0.90 while the lower-wage contractor gets 1.08.

A contractor paying better wages can therefore post a lower mod on the same safety record, because payroll sits in the denominator and moves the ratio by itself. Antonello names a second distortion: in states that report losses net of a deductible, a contractor can buy down its mod by buying a deductible.

The real source of the 1.0 threshold

The common claim that any mod above 1.0 disqualifies you doesn't match the published rules. Real prequalification standards sit above it and vary widely, and rules that do cite 1.0 usually define an acceptable safety record rather than bar a bidder. If a denial rests on your mod, quote NCCI's own position back to the reviewer, then offer your claim record. What a mod above 1.0 costs a contractor covers the premium side.

Do I even have an experience modification rate?

Only employers whose premium clears a state qualification amount are experience rated. Below that line a contractor pays manual rates with no mod at all. Once you clear it, experience rating is mandatory. The test can be met two ways: enough subject premium in the most recent 24 months, or enough as an average across the experience period.

The amounts are filed state by state and revised upward over time, so the threshold that made you rated in one state will not be the number in the next. Colorado's 24-month amount, for example, runs $11,000 to $12,500 across the 2024 to 2026 rating years. Two consequences catch contractors out. An employer whose premium keeps declining can lose eligibility and revert to a unity 1.00. A new business can also qualify on its first policy and be rated from under 12 months of data. That is why the common claim that new companies hold 1.0 for three years isn't a rule.

Which three years is my mod actually built on?

Your experience modification rate uses policies with effective dates no less than 21 and no more than 57 months before the rating effective date. That window excludes your most recent completed policy year, because loss data needs time to mature. A clean current year can't show up in the mod that prices your next renewal.

Insurers need not report a policy's data until 18 months after inception, and the mod is generally calculated 60 to 90 days before the rating effective date. It reads the loss run your mod is built from, valued long before renewal, per NCCI's experience rating guide. For a January 1, 2026 rating date the window lands like this:

When does the number actually lock?

Open claims enter at their valued amount, so the valuation date is the moment a policy year's data locks for that mod. Under NCCI's unit statistical reporting rules, a reserve change after that date is not a reportable correction, though noncompensable claims, fraud findings and final audit results are. So the window to revalue a reserve or reclassify a claim closes before that date.

One controller at a $45 million mechanical subcontractor pulled her worksheet in May and started with the open claims. A knee claim from the 2023 policy year was still carried at $165,000, a year after the worker returned to full duty. Her adjuster revalued it to $58,000 before that year's next valuation, so the lower figure fed the mods that followed. Coverwatch pulls the worksheet and reconciles reported payroll and open reserves against the claims record, challenging what is contestable before the data is filed, on a flat fee.

Who calculates my mod, NCCI or my state?

NCCI administers experience rating in most jurisdictions, but not all. Eleven states run their own independent rating bureaus. NCCI's Experience Rating Plan Manual doesn't apply at all in six of them: California, Delaware, Michigan, New Jersey, New York and Pennsylvania. Four states sell workers compensation only through a state fund, each on its own formula.

WCIRB's California plan puts full weight on primary losses and none on excess. It scales its primary threshold across 92 size tiers from $4,500 to $75,000 instead of using one split point, and drops the first $250 of every claim. The experience modifier workers comp carriers use in California and a Nevada mod built from the same loss run come out at different numbers.

A multi-state contractor can carry two mods at once. Minnesota and Wisconsin produce their own intrastate mods and combine with NCCI only for interstate rating. A contractor working in Minneapolis and Des Moines holds a Minnesota mod and an interstate mod, each under a different formula. Which number a general contractor sees depends on which mod it requests.

Why does my mod barely move after a big claim but jump after three small ones?

Because experience rating splits every claim at a state-filed split point. Dollars below it count in full as primary losses, and dollars above it count only at a weighted fraction. That mechanism, called split rating, means several small claims can generate more primary loss than one large claim of the same total value.

A companion post works through what one claim costs across three years of mod.

NCCI began replacing the single countrywide split point with state-specific values in filings effective on or after November 1, 2023. The $18,500 figure repeated across insurance blogs is the last countrywide value, so any split point quoted without a state and a date came from there.

The cap on a single large claim

A single catastrophic loss also stops counting at a filed ceiling, the state per claim accident limitation. Colorado's January 1, 2026 filing sets it at $138,500, so a $400,000 lost-time claim enters at $138,500 and one accident caps at twice that.

Contractor size decides how much of that arithmetic reaches the mod, because weighting and ballast values both scale with expected losses. A contractor with $3 million of expected losses gets far more of its own record into the result than one with $100,000. Medical-only claims arrive reduced by 70% under the experience rating adjustment.

The mod is a payroll-weighted rating factor, and the levers change shape once you see it that way: reported data and the filing calendar matter alongside the loss record. Once you know which inputs move, the next step is a three-year plan to lower your mod, sequenced across the full experience period.