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Severity Rate & Lost Time Rate Calculator

A severity rate answers a different question from TRIR: not how many people were hurt, but how much time the injuries cost. Enter the day counts and case counts from your OSHA 300A summary and this calculator returns the day count rate OSHA's own worksheet defines, your lost time case rate, and the average days behind each case.

Calendar days, counted from the day after the injury, whether or not the employee was scheduled to work (1904.7(b)(3)(i) and (iv)).
A partial day of work counts as a full day of restriction, except on the day the injury happened (1904.7(b)(4)(v)).
The number of cases, not the number of days. Used for the lost time case rate and for the days-per-case averages.
Cases with restricted work or transfer and no days away.
hours
Actual hours worked, overtime included. Vacation, sick leave and holidays are excluded even when paid.

Rates and totals are calculated only from the numbers you type, so they are only as good as your OSHA 300 Log. This page is not an OSHA form, is not submitted to anyone, and does not decide whether a case is recordable — that follows 29 CFR Part 1904 and, in a State Plan state, your state's own rule. Nothing you type is sent to our servers.

Three different things called “severity”

Ask three safety managers for their severity rate and you will get three formulas. None of them is wrong; they answer different questions, and the only one with an OSHA name behind it is the first.

What people mean by severity, and where each comes from
MetricFormulaReads asSource
Day count rate(K + L) × 200,000 ÷ hoursDays lost or restricted per 100 full-time workers per yearOSHA's own incidence rate worksheet
Days per caseK ÷ HHow long the average lost time case kept someone off workCommon practice, no OSHA definition
Lost time case rate (LTIR, LTIFR)H × 200,000 ÷ hoursCases with days away per 100 full-time workersCommon practice — not the DART rate

Before comparing your number with anyone else's, ask which columns they used. A “severity rate” of 60 and one of 22.5 can come from exactly the same year at the same company.

Counting days: the rules that trip people up

  • Start the day after. Counting begins on the day after the injury occurred or the illness began — never the day itself (1904.7(b)(3)(i)).
  • Calendar days, not scheduled days. You count the calendar days the employee was unable to work, whether or not the employee was scheduled to work on them (1904.7(b)(3)(iv)). Weekends, holidays and a plant shutdown inside the absence all count.
  • A partial day is a full day of restriction — except on the day of the injury (1904.7(b)(4)(v)).
  • 180 is the ceiling for one case. Once a case passes 180 calendar days away and/or of job transfer or restriction, you are not required to keep counting: entering 180 in the total days away column is adequate (1904.7(b)(3)(vii)).
  • Cases do not cross years. A case is recorded once, in the year it occurred. If the employee is still away when the year closes, you enter your best estimate of the total days and correct the entry later if it turns out wrong (1904.7(b)(3)(ix)).
  • An employee who leaves. If someone leaves the company for reasons unrelated to the injury, counting stops. If the departure is because of the injury, you estimate the days the case would have caused (1904.7(b)(3)(viii)).

How to read a day-based rate

Day counts concentrate in very few cases, which makes these rates informative about cost and poor for month-to-month comparison. One back injury with a 90-day absence adds 72 points to the day count rate of a 250,000-hour establishment; ten cases that ended in stitches and a tetanus shot add nothing at all. That is not a defect — it is the whole point of measuring days instead of cases — but it means the number swings hard and should be read over three years, always next to the case counts behind it.

There is also nothing to benchmark it against. OSHA's own rate worksheet notes plainly that no comparable rate is published for day counts, unlike the case-based rates, where BLS publishes averages by industry and establishment size. Compare your day count rate with your own history, or with your own target — not with a number someone quotes at a conference.

One more caution: a fatality produces no days at all. An establishment with one fatality and nothing else has a day count rate of zero. Keep the case-based rates and the fatality count on the same page as this one.

What actually moves the number

Two things, and only one of them is safety. Fewer serious cases lower it; so does bringing people back on genuine transitional duty, because days of restriction are counted in column L while days away are counted in column K, and a case that returns to modified work stops adding days away. That is legitimate — it is also why a falling day count rate should be read alongside a stable case count before anyone claims a safety improvement.

The cases that fill these columns are predictable ones: manual handling, falls to a lower level, and being struck by something. The NIOSH lifting equation is the standard way to put a number on the first, and a job hazard analysis on the task is how the other two get found before they are recorded.

How it's calculated

Day count rate (severity rate)
day count rate = ((column K + column L) x 200,000) / hours worked
OSHA's own worksheet calls this the Day Count Rate. Read it as days lost or restricted per 100 full-time workers per year.
Lost workday rate (days away only)
lost workday rate = (column K x 200,000) / hours worked
The same rate counting only days away from work, for organisations that track days away separately from restricted duty.
Lost time case rate
lost time case rate = (column H x 200,000) / hours worked
Cases with days away from work per 100 full-time workers. Often called LTIR or LTIFR; it is not an OSHA-defined metric, and it is not the DART rate, which also counts restricted-work cases.
Average days away per lost time case
days per case = column K / column H
The other thing people mean by severity: how long the average case kept someone off work.
Average days per DART case
days per DART case = (column K + column L) / (column H + column I)
Days away and restricted days spread over every case that took someone off the job or off normal duties.
What 200,000 is
200,000 = 100 employees x 40 hours/week x 50 weeks/year
The same base as every OSHA incidence rate, so day-based rates can be read on the same per-100-workers scale.

Frequently asked questions

The version with an OSHA source behind it is the day count rate: add column K (total days away from work) and column L (total days of job transfer or restriction) from your 300A summary, multiply by 200,000 and divide by the hours worked. Example: 45 days away plus 30 restricted days over 250,000 hours gives (75 x 200,000) / 250,000 = 60 days per 100 full-time workers. The other common meaning of severity is simply days divided by cases — 45 days over 2 cases is 22.5 days per case.

OSHA does not use the phrase severity rate in Part 1904, and Part 1904 never requires you to compute any rate. What OSHA does publish is a worksheet that names three rates from the 300 Log columns: a total injury and illness rate from columns G, H, I and J, a DART rate from H and I, and a day count rate from K and L. The day count rate is the one that measures days, and that worksheet notes there is no comparable BLS rate to compare it against.

Calendar days. 1904.7(b)(3)(iv) requires you to count the number of calendar days the employee was unable to work, whether or not the employee was scheduled to work on those days — so weekends, holidays and shutdown days inside the absence all count. Counting starts the day after the injury occurred or the illness began, never the day of the injury itself.

1904.7(b)(3)(vii) lets you stop counting at 180 calendar days for a single case, whether those days are days away, days of restriction, or a combination. OSHA's words: you are not required to keep track of the days once a case passes 180 calendar days away and/or of job transfer or restriction, and entering 180 in the total days away column is adequate. Long cases are exactly where the cap matters: without it, one serious injury can dominate a day-based rate for years, and the rate stops saying anything about the year you are measuring.

The lost time case rate counts only cases with days away from work — column H. The DART rate counts those plus cases with job transfer or restriction — columns H and I. So a lost time rate is always lower than or equal to a DART rate. LTIR and LTIFR are common names for a lost time rate, but they are not OSHA terms and different companies define them differently, so ask which columns someone used before comparing numbers.

No. A fatality is recorded in column G and gets no entry in the day columns — there are no days away to count. This is one reason a day-based rate should never be read on its own: an establishment with one fatality and no other cases has a severity rate of zero. Keep the case-based rates and the fatality count alongside it.

No. 1904.7(b)(3)(ix) records the case only once, in the year the injury occurred, and if the employee is still away when you close the year you enter your best estimate of the total days. If the employee leaves the company because of the injury, 1904.7(b)(3)(viii) also asks for an estimate of the days away the case would have caused. If your estimate later proves wrong, correct the log entry.

Because days concentrate in very few cases. One back injury with a 90-day absence adds 72 points to the day count rate of a 250,000-hour establishment, while ten first-aid-plus cases with no lost time add nothing at all. Day-based rates are useful for showing what injuries actually cost in time, and poor for month-to-month comparison. Look at them over three years, alongside the case-based rates, and always with the number of cases behind them.

Sources & references

Content checked against these sources — last reviewed August 28, 2026.

By — Editorial team of SteelToeTools.com (published by LSEA SAS) Updated v1