Experience mod (EMR) calculator

How to use it

The tool needs numbers from your experience rating worksheet, which your insurer or the rating bureau issues each year. Every default shown is an example; overwrite it.

• Expected losses (E). The total expected losses on the worksheet.
• D-ratio. The weighted share of expected losses that is primary.
• Weighting value (W). Larger employers carry a larger W.
• Ballast (B). From the worksheet.
• Split point. Where a claim divides into primary and excess. Each NCCI state has its own, indexed with its loss cost filing, so copy yours from the worksheet. The $20,000 shown is an example only.
• Per-claim accident limitation (optional). The state's cap on any one claim. Leave blank to ignore.
• ERA checkbox. Counts medical-only claims at 30%. Your worksheet shows whether your state applies it.
• Manual premium per year, payroll ÷ 100 × rates, before the mod. This only drives the cost column.
• Claims, up to six: a description, the incurred amount (paid plus reserves, as on the worksheet) and a medical-only box.

The math

A medical-only claim with the ERA on is first reduced to 30% of its value. Each claim is then capped at the accident limitation if you entered one, and split: the first dollars up to the split point are primary; the rest is excess.

With Ep = E × D-ratio and Ee = E − Ep:

Mod = (Ap + W·Ae + (1 − W)·Ee + B) ÷ (Ep + W·Ee + (1 − W)·Ee + B)

Ap and Ae are actual primary and excess losses. The bottom line simplifies to E + B. The tool shows each piece, rounds the mod to two decimals and prints the unrounded value too. It also recalculates the mod without each claim, and multiplies the change by your manual premium and by three years.

Hypothetical: E = $40,000, D-ratio 0.35, W = 0.10, B = $25,000, split point $20,000. A $40,000 lost-time claim gives $20,000 primary and $20,000 excess. A $5,000 medical-only claim at 30% gives $1,500 primary. Ap = $21,500, Ae = $20,000, so the top is $71,900 against a bottom of $65,000: a mod of 1.11. Without the big claim the top is $49,900 and the mod is 0.77. On $60,000 of manual premium, the difference is 0.34 × $60,000 × 3, about $61,200.

Assumptions and limits

• Your worksheet is the authority. This reproduces the arithmetic from figures you supply. It does not know which claims belong in the experience period, how they were valued or whether a claim was later revalued.
• Order of the ERA. The tool reduces a medical-only claim to 30% before splitting it, as NCCI describes the adjustment, so a $100,000 medical-only claim rates as $30,000: $20,000 primary and $10,000 excess at a $20,000 split point. If your worksheet shows something different, the worksheet governs.
• Same premium three years running. The cost column assumes your manual premium is constant for the three years a claim stays in the experience period.
• Rounding. The cost column uses the mods rounded to two decimals.
• Not every state. The NCCI plan does not apply in California, Delaware, Michigan, New Jersey, New York or Pennsylvania, which have their own rating plans, or in the monopolistic-fund states. Check with your bureau.
• Frequency beats severity. Primary losses count in full while excess losses are mostly replaced by expected excess, so several small claims raise a mod more than one large one. Reporting injuries promptly and managing return to work help keep small claims small. See return-to-work programs: how to build one.

Use the result to explain a mod, test a "what if" or challenge a worksheet error. Ask your broker or the bureau for a review if you think a claim is miscoded or unrelated to your operations. Read The experience modification rate (EMR) explained and how to lower your workers' comp costs; see the effect on premium in the workers' comp premium calculator.

Where the figures come from

• NCCI, ABCs of Experience Rating (2025): split rating, the ERA at 30% for medical-only losses and the three-year experience period.
• NCCI, Experience Rating Plan Methodology Update FAQs: state-specific split points.