Severity Rate Calculator

The severity rate answers a different question from the incident rate: not how often people get hurt, but how many days of work those injuries cost. This calculator runs the OSHA-style formula, lost workdays times a base divided by total hours worked, with the right base for your review cycle: annual, quarterly or monthly. It also shows the full-time-equivalent headcount behind the number and the average days lost per incident.

Quick Answer

How to use the severity rate calculator

Enter lost workdays and total hours worked, pick the period that matches your review cycle, and click Calculate. Results stay hidden until you click.

1. Lost workdays: the total days employees could not work because of recordable injuries or illnesses. Count calendar days starting the day after the injury, capped at 180 days per case under OSHA’s recording criteria.
2. Total hours worked: every hour actually worked by everyone in scope during the same period, overtime included. Leave out vacation, sick leave and holidays.
3. Period: annual uses the 200,000 base, quarterly uses 50,000, monthly uses 16,667. Match it to the period your days and hours cover, or the rate misleads.
4. Lost-time incidents (optional): how many separate incidents produced the lost days. The tool divides days by incidents for the per-incident average; leave it at 0 to skip that line.
5. Read the result line by line: the rate itself, the days-over-hours framing with an FTE estimate, the BLS comparison block, and the printed formula you can check by hand.

The formula, and why the base is 200,000

Severity rate = (lost workdays × base hours) ÷ total hours worked. The 200,000 base is 100 full-time employees working 2,000 hours a year, so the annual rate reads as lost workdays per 100 FTE.

The base exists so a 50-person shop can compare itself to a 5,000-person enterprise: raw lost-day totals would make every large employer look dangerous simply because of headcount. The same 200,000 constant sits under the incidence rate and the DART rate, which is why all three can be tracked on one dashboard. The National Safety Council’s benchmarking guide walks through calculating your rates and comparing them to BLS-published industry averages, which is the honest way to judge whether your number is good.

Worked example: 45 lost days, plus verified runs

The pre-filled run is a mid-size plant’s year: 45 lost workdays, 500,000 hours worked, 9 lost-time incidents. Every row below is a verified run of the calculator above.

The quarterly row shows why the scaled base matters. Twelve days over 125,000 hours is a 4.80 quarterly rate; if that pattern held all year, the annual rate would be about 19.2, close to the worked example’s 18.00. Running the same days against the annual 200,000 base would print a rate four times larger and alarm nobody who knows better. For the monthly row, check the arithmetic: (8 × 16,667) ÷ 84,000 = 133,336 ÷ 84,000 = 1.59, exactly what the tool prints, and the FTE line reads ~503 because 84,000 ÷ 167 is about 503 workers’ worth of monthly hours.

Severity is not frequency: pair this with the incident rate

Two companion metrics complete the picture. The incidence (frequency) rate counts recordable incidents per 200,000 hours: how often people get hurt. The severity rate counts days lost: how badly. A site can have high frequency and low severity (many minor cuts) or low frequency and high severity (one amputation), and the two numbers together distinguish a nuisance pattern from a catastrophe pattern.

The tool’s average-days-per-incident bridges the two views: it is the severity numerator divided by the frequency numerator. The DART rate counts cases involving days away, restriction or transfer per 200,000 hours, so DART answers “how many serious cases” while severity answers “how much work was lost”. Report them side by side on the same slide; a rate standing alone invites the wrong conclusion. Lost days also carry a price tag, so run the days through a cost-of-accidents estimate when the safety conversation needs a dollar figure.

Day-counting rules the rate depends on

The arithmetic is simple; the counting is where severity rates go wrong. Three rules keep the number honest across periods and sites.

OSHA counts calendar days, not scheduled workdays: weekends and holidays count if the employee would have been unable to work, and counting starts the day after the injury, never the injury day itself, per the general recording criteria in 29 CFR 1904.7. Restricted or light-duty days are tracked separately on the OSHA 300 log and may or may not belong in your severity definition, so publish the rule next to the KPI and apply it consistently. The 2024 BLS figure comes from the Bureau of Labor Statistics employer-reported injuries and illnesses release. And note the honesty limit that used to sit here: the tool previously printed its own Low / Moderate / High labels for trending, not regulatory thresholds. Those labels are removed; the result now compares your components with national BLS figures instead, which is stated under the result on the calculator itself.

Compare to your industry, not to a universal band

BLS publishes no OSHA severity rate by industry, so there is no industry severity number to match and no universal good or bad band to print. What BLS does publish, in the Survey of Occupational Injuries and Illnesses (SOII), are the components behind severity: how often days-away cases occur, and how long they last. Compare those components, not a verdict.

For a sector check, pick your industry in the calculator, then find its row in the BLS SOII industry tables and compare the same components: your sector’s days-away case rate and the national median days away. A rate above the national figures is a prompt to investigate your largest incidents, not a grade. The BLS employer-reported injuries and illnesses release is the source for the national figures in this table.

What competing calculators miss

The rival tools ranking for this keyword mostly assume the annual 200,000 base and stop:

• HSEBlog’s severity rate calculator: the strongest of the group, with both OSHA (200,000) and ISO (1,000,000) bases, day-counting rules, and a severity-versus-frequency section. No quarterly or monthly base, no per-incident average, no FTE framing.
• OSHEBlog’s severity tool: good key points (publish your restricted-day rule, show severity beside frequency, state fatality day-charging). A thin tool around them: annual-only, no incident input.
• HSEWindSock’s OSHA incident rate calculator: the only rival that calls out the 180-day cap per 29 CFR 1904.7(b)(3)(vii) and adds an average-days-per-case note. Severity is a secondary section, and there is no period scaling.
• ImpactTech’s severity rate calculator: ISO 45001 framing, calendar-day convention, injury-day exclusion, Column I restricted-day note. Pre-filled zeros and no FTE or period options.
• HSEBlog’s LWR calculator: a nice OSHA-style twin of ISO severity with the ×5 conversion stated plainly. Annual-only, no incidents input, no interpretation.
• The gap this page fills: quarterly and monthly bases for the reviews safety teams actually run, the per-incident average that bridges frequency and severity, an FTE estimate so the hours mean something, and a BLS comparison in place of invented authority bands.

Frequently asked questions

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References