Two sites can have the same number of injuries and be very different places to work. At one, people are back the next day. At the other, they are off for months. The severity rate shows that difference.
Add your days lost and hours worked to the calculator, choose your base, and see the result.
What is the severity rate?
The severity rate measures how serious your injuries are by counting the days lost to injury, compared with the hours worked. Frequency rates tell you how often people get hurt. Severity tells you how much it hurt the business and the person.
The severity rate formula
Severity rate = (Days lost x base) / Total hours worked
The base is usually 1,000,000 or 200,000 hours. Different standards and companies choose different ones, so the calculator lets you pick. Always write the base next to your result.
What counts as days lost?
Days lost are the days a person could not work because of a work injury. Companies differ on the details: some count calendar days, some count scheduled working days, and some assign standard charges for serious cases. Choose your rule once and apply it every time.
Worked example
A site lost 45 days to injuries in a year and worked 400,000 hours.
- Per 1,000,000 hours: (45 x 1,000,000) / 400,000 = 112.5
- Per 200,000 hours: (45 x 200,000) / 400,000 = 22.5
Both results describe the same site. Only the base is different, which is why stating it matters.
Find the average days per injury
You can learn more by dividing days lost by the number of lost-time injuries. If those 45 days came from 3 injuries, each injury cost 15 days on average. A site with 3 injuries and 12 lost days is in a very different position, even though the injury count is the same.
Frequency vs severity
Look at both together. The LTIFR tells you how often lost-time injuries happen. Severity tells you how heavy each one was.
- High frequency, low severity: many small injuries. Look at everyday habits.
- Low frequency, high severity: few injuries but serious ones. Look at high-risk tasks.
- Both high: urgent action needed.
- Both low: keep checking and keep reporting.
How to use the result
Do not stop at the number. Open the injury reports behind it. A single long absence can pull the rate up a lot, and the fix is usually in that one case: a missing control, a task that needs redesign or poor medical follow-up.
Common mistakes
- Mixing bases between reports
- Counting days differently from month to month
- Forgetting days from injuries that carry over from the previous year
- Ignoring one very long case that distorts the whole figure
Example: two sites with the same injuries
Site A and Site B each had 4 lost-time injuries and 400,000 hours worked. Site A lost 20 days in total. Site B lost 120 days. Their frequency is the same. Using the 1,000,000 base, Site A has a severity rate of (20 x 1,000,000) / 400,000 = 50. Site B has (120 x 1,000,000) / 400,000 = 300. Site B’s injuries are six times heavier. Without severity you would never see that.
Step by step
- Add up all the days lost for the period.
- Add up the total hours worked.
- Choose your base, 1,000,000 or 200,000.
- Multiply days lost by the base.
- Divide by the hours, and write the base next to the answer.
Questions to ask when severity is high
Which injuries caused the most lost days? Were they preventable? Did the person get good medical care and a proper return-to-work plan? Sometimes a better recovery process cuts lost days without changing the number of injuries at all.
Using severity in your report
When you write a safety report, show frequency and severity side by side, with a short comment on each. For example, say that injuries stayed the same but days lost doubled, mainly because of one long absence. Then state what you are doing about it. A number with a clear story and an action is far more useful than a number on its own.
Frequently asked questions
What is a good severity rate?
There is no single answer. Compare with your own history and with similar work.
Is the severity rate the same as LTIFR?
No. LTIFR counts the number of lost-time injuries. Severity counts the days lost.
Which base should I use?
Use the one your client or reporting standard asks for. If there is none, pick one and keep it.
Do restricted days count?
Some organisations count them, others do not. Check your own definition.
Why does one case change my rate so much?
A very long absence adds many days at once, so the rate moves a lot. That is normal in small teams.
Learn this properly
Understanding frequency and severity is part of NEBOSH, IOSH and OSHA training. ISH Institutes teaches these courses in Peshawar. Chat with us on WhatsApp and we will help you pick the right course.