Published October 2026.
Direct Answer: Your workers’ compensation experience modification factor—often called the ex-mod or mod—is a multiplier on your state-approved manual premium that compares your past loss history to employers with similar payroll and job classifications. A mod of 1.00 means average loss experience; 1.25 means you pay roughly twenty-five percent more than the average peer, and 0.85 means a fifteen percent credit. The number comes from a standardized formula (NCCI in most states) that weights frequent small claims heavily, looks back at a rolling three-year window of paid and reserved losses, and updates annually—so contractors who control claim frequency, return injured workers safely, and keep reserves accurate can move the mod down over two to three policy cycles.
General contractors request that decimal because it is a bureau-verified pricing signal. It sits inside workers’ compensation insurance, classification, and experience rating. When you know how the multiplier is built, a 1.25 mod becomes a line item on every bid instead of a renewal surprise.
What the experience modification factor actually is
The experience modification factor adjusts manual workers’ compensation premium for one employer based on historical loss experience relative to peers. Manual premium is payroll in each classification multiplied by the filed rate for that class in your state. The mod multiplies that total before insurer discounts, schedule credits, and taxes.
A mod of 1.00 is the neutral pivot: loss experience in line with actuarial expectation for your size and mix of work. Mods above 1.00 are debits (premium increases). Mods below 1.00 are credits (premium decreases).
Experience rating applies where state rules require or allow it. Employers below the payroll threshold often stay at a neutral 1.00; mid-size and large contractors usually carry a calculated mod. Thresholds vary by state and rating organization.
Who publishes the number. In most states, NCCI calculates mods under the Experience Rating Plan from insurer unit statistical data. NCCI does not sell insurance. Independent bureaus in states such as California use parallel concepts. Insurers apply the bureau mod unless state law permits a narrow alternative.
The mod on renewal is effective for the upcoming policy period, computed from carrier data—not negotiated with your agent. Wrong classes, missing subrogation, or stale reserves distort it until the bureau corrects the record.
The NCCI formula in plain English
Actuaries compare actual losses to expected losses for your payroll and classifications, then stabilize the outcome so one catastrophe cannot dominate a modest contractor’s mod. Read the published formula as four concepts: expected losses, split losses, ballast, and weighting.
Actual losses versus expected losses
Expected losses are what a statistically average employer with your audited payroll in your class codes would incur over the experience period. Each code carries an expected loss rate per $100 of payroll; multiply, sum, and you have expected loss dollars before splitting.
Actual losses are claims that count in experience rating for the same window—generally indemnity and medical (plus employer liability where applicable), subject to catastrophe rules and single-claim caps. Figures come from insurer reports: paid loss plus case reserves on open claims.
Equal actual and expected losses, with neutral stabilizers, land near 1.00. The split point, ballast, and weighting convert any gap into the single multiplier on your proposal.
The split point: primary versus excess losses
Each claim is divided at the split point, a threshold in the rating plan that changes over time. Dollars at or below the split are primary losses; dollars above are excess losses.
Primary losses drive the mod at full strength against expected primary losses. Excess losses still count but are discounted—they move the mod more slowly. The split point keeps one severe injury from swinging the factor as sharply as the first dollars of many smaller claims.
Ballast and weighting: stabilizing small employers
Ballast is added to numerator and denominator so extreme mods regress toward 1.00 when expected losses are small. Without it, thin payroll plus one bad year could produce an uninsurable mod.
Weighting calibrates how much credibility your own experience earns given expected loss size. Larger expected totals let your data speak louder; smaller totals lean on ballast and the industry mean. Two contractors with the same actual-to-expected ratio can therefore receive different mods when payroll scale differs.
A simple numeric illustration (conceptual)
Suppose expected losses total $100,000 for the period (already split into expected primary and excess on a real worksheet). Actual primary is $90,000 and actual excess is $40,000—round numbers for direction only.
Actual primary below expected primary pulls the mod down; actual primary above expected—common when several moderate claims each fill the primary layer—pushes it up without any single huge loss. Excess above expectation nudges upward with less leverage. Ballast adds a stabilizing slice to both sides so the bureau can publish, say, 0.92 or 1.18 without using one naive ratio. Request the experience rating worksheet from your agent to see claim-level splits and the final calculation.
Why small claims hurt more than you think
Contractors often fixate on catastrophic injuries. Frequency drives many debits because every claim stacks primary dollars up to the split point.
Three strain injuries at $15,000 incurred each may load primary losses three times. One $45,000 file hurts, but the plan often treats multiple moderate files as a controllable pattern rather than a single mishap.
Severity above the split still matters, yet discounted excess means each additional primary dollar bites harder. Return-to-work that shortens indemnity, or early treatment that avoids escalation, trims primary totals even when medical trend inflates industry costs.
Inflated reserves on open claims count as actual loss until reduced. Reserve reviews with the carrier are mod management, not paperwork. Job-site habits—fall protection, housekeeping, fleet standards—cut frequency in ways slogans do not. Documenting hazards aligns with property risk assessment and quantifying hazards even when the immediate goal is workers’ compensation experience.
How long losses follow you
Experience rating uses a rolling three-year period plus a lag year so claims can mature—the window often ends two years before the mod effective date.
Each calculation drops the oldest year and adds a newer one. Improvement is a three-year project.
A mod effective January 1, 2027 might use policy years 2022–2024 with 2025 in lag—dates follow your anniversary and state rules. Closing files, subrogation, and correct medical-only coding shorten how long dollars stay in the window.
How contractors lower the mod
Lowering the mod means lowering actual losses relative to expected losses over the experience period—not bargaining with the bureau. Safety, claims, and payroll reporting are one system.
Safety programs that actually move the number
Enforced fall rules, pre-task plans, fleet telematics, and substance policies cut frequency and severity. The mod responds to reported dollars, not binder thickness—fewer or smaller losses on the worksheet are what move the number.
Return-to-work and transitional duty
Indemnity duration feeds primary loss on partial disability; modified duty within restrictions limits wage replacement. Confirm state counting rules with your claims professional.
Claim reporting discipline
Late notice worsens outcomes and reserves. Early reporting meets statutory duties and preserves investigation. Field leaders should know first notice of loss, duty to report, and notice requirements before an injury occurs.
Fighting fraudulent and exaggerated claims
Coordinated statements, independent medical exams, and subrogation against responsible third parties keep reserves and history accurate.
Premium size and classification accuracy
Misclassified payroll lowers expected losses and makes actual losses look worse—a silent mod penalty. Audit payroll and split office versus field where permitted. When restructuring coverage, commercial insurance program design should align class codes with how work is performed.
Owners reviewing subs weigh workers’ compensation experience alongside general liability limits. Understanding commercial general liability coverage structure does not change the mod, but a tight comp history pairs with credible overall risk transfer.
What the mod costs on bids
The mod multiplies manual premium—the piece of workers’ compensation most sensitive to your loss record—not total revenue. On bids the math is still decisive.
Manual premium at mod 1.00 of $200,000 becomes $200,000 × 1.25 = $250,000 at a 1.25 mod before other carrier adjustments. That is $50,000 in one year from experience rating alone—margin, bond capacity, or crew hours you cannot spend elsewhere on a fixed price.
At mod 0.90, the same base is $180,000, saving $20,000 annually versus 1.00—a spread that compounds across the three-year experience window.
General contractors screen subs by mod because it is standardized and cheap to verify. A 1.30 mod can disqualify you; a 0.95 mod can win tie-breaks when labor is tight—alongside EMR on public work and limits on certificates.
Premium breakdowns on proposals tie the worksheet to cash. How to read insurance policy declarations shows where debits and credits land on the declaration page.
Base rates still move with medical inflation and legal trend—see social inflation and insurance pricing—while the mod is the lever you control through loss experience.
Insurance policy form filing and state DOI approval describes how filed loss costs become manual premium—the base the mod multiplies.
FAQ
What is an experience modification factor?
An experience modification factor is a multiplier applied to your workers’ compensation manual premium based on your historical loss experience compared to employers with similar payroll and job classifications. A mod of 1.00 indicates average experience; values above 1.00 increase premium (debit), and values below 1.00 decrease premium (credit). In most states the factor is calculated by NCCI or a state rating bureau using standardized data reported by your insurers.
How does the NCCI experience rating formula work?
The NCCI plan compares actual losses to expected losses for your classifications and payroll over a defined experience period. Individual claim amounts are split at the split point into primary losses (weighted heavily) and excess losses (discounted). Ballast and weighting terms stabilize the result so small employers are not overwhelmed by random volatility. The bureau publishes a single mod factor from that computation, which insurers apply to manual premium.
Why do small workers’ comp claims raise my mod more than I expect?
Because primary loss dollars—those at or below the split point on each claim—count strongly in the formula, multiple moderate claims can produce a high mod even without a catastrophe. Frequency stacks primary layers against expected losses. Excess dollars from large claims still matter but move the mod more slowly. Open claims with high reserves also count until closed or reduced.
How long do losses affect my experience mod?
Typically three experience-rated policy years, excluding the most recent year as a lag period so claims can develop. Each annual recalculation drops the oldest year in the window and adds a newer year. Improvement therefore usually requires sustained better results across several years, not a single good quarter.
How can a contractor lower its experience modification factor?
Lower actual losses relative to expected losses over the experience period: reduce claim frequency with enforced safety programs, use return-to-work to limit indemnity, report claims promptly, challenge fraudulent or inflated claims, recover subrogation, and keep payroll classifications accurate so expected losses are correctly stated. Correct bureau data errors when they appear on the worksheet.
What does a 1.25 mod vs a 1.00 mod actually cost on a bid?
Multiply your manual workers’ compensation premium by the mod. If manual premium is $200,000, mod 1.00 yields $200,000 before other adjustments; mod 1.25 yields $250,000—a $50,000 annual difference from experience rating alone. On tight bids that gap equals labor, bond, or profit margin general contractors expect subs to carry efficiently.