TRIR and LTIFR: how the numbers are actually calculated

TRIR and LTIFR are the two numbers that end up in a board pack, a tender response and a client audit. They are also the two most commonly miscalculated, because the formula is simple and the inputs are not.

The formulas are the easy part

Total Recordable Incident Rate is recordable cases multiplied by a constant, divided by exposure hours. Lost Time Injury Frequency Rate is the same shape with lost-time injuries on top. The constant is where the first disagreement starts: 200,000 is common in North America and represents 100 employees working a year, while 1,000,000 is common elsewhere. A rate quoted without its constant is not a number, it is a rumour.

Exposure hours are where it goes wrong

The denominator is total hours actually worked by everyone exposed, and almost every mistake lives here. Contractors are in or out depending on your reporting scope. Overtime counts. Leave does not. Using headcount multiplied by a nominal year is an estimate, and estimating the denominator makes the rate an estimate too.

If exposure hours are derived from real workforce data rather than typed in each period, the number stops drifting between reports, which is usually the first thing an auditor notices.

What counts as recordable is a decision, not a fact

First aid is generally not recordable. Medical treatment beyond first aid generally is. Restricted work and job transfer count. The boundaries are defined by whichever standard you report under, and reasonable people place cases differently near the line.

The important thing is not which convention you pick, it is that the same one is applied every period and that the classification is attached to the case rather than applied later in a spreadsheet.

Why the formula needs to be editable

Organisations report to different conventions, and a client or regulator may require one you do not use internally. Software that hard-codes a single formula forces the numbers back into a spreadsheet, at which point the system is no longer the source of truth and the audit trail stops at the export.

What this looks like in HSE360

HSE360 derives exposure man-hours from workforce data and computes TRIR, LTIFR and similar rates on formulas that are configurable per organisation, so the output matches the convention you actually report under. Recordability follows the case classification captured at the time, not a later judgement.

The report builder then assembles branded PDF and Excel packs with period-over-period deltas, which is usually the form the question arrives in.