What this comparison works out
This tool takes minimum and maximum estimates from three independent indicators — algor, rigor and livor mortis — and finds the interval where all three overlap.
It reflects how post-mortem interval estimation actually works. No single indicator is relied on. Each gives a range, and the useful conclusion is where the ranges agree. These tools are teaching aids. They are not validated for casework, and no result from them should appear in a statement, report or investigation.
Enter estimated ranges
| Indicator | Minimum hours | Maximum hours |
|---|---|---|
| Algor | ||
| Rigor | ||
| Livor |
Before you compare ranges
- Each range should come from an appropriate method applied to the case, not from a textbook average.
- Ranges should be honest. A narrow range entered because it looks decisive produces a false overlap.
- The indicators must be genuinely independent. Two methods sharing an assumption do not corroborate each other.
- An empty overlap is a result, not a failure. It usually means one estimate is wrong or the assumptions differ.
Three ranges agreeing on a six-hour window is a stronger conclusion than one method producing a two-hour window. Narrowness is easy to manufacture by understating uncertainty; agreement between independent methods is not.
How this calculator works
The intersection of the ranges:
Overlap lower bound = the largest of the three minimums
Overlap upper bound = the smallest of the three maximums
If the lower bound exceeds the upper bound, there is no common intervalThe intersection is the standard way to combine constraints. It assumes each range genuinely contains the true value — if one does not, the overlap is misleading rather than merely narrow.
The tool treats the three indicators equally. In practice they are not equally reliable, and their reliability changes with the interval: rigor is informative in the first day or so, livor becomes fixed within a similar period, and temperature loses value as the body approaches ambient.
Worked example: three indicators
Using the default figures — algor 6 to 12 hours, rigor 4 to 18, livor 2 to 12:
- Largest minimum: 6 (from algor)
- Smallest maximum: 12 (from algor and livor)
- Common overlap: 6 to 12 hours
The algor range is doing most of the work here — it sets both bounds. Rigor's 4 to 18 window constrains nothing, which is a useful thing to see. If the algor estimate turned out to rest on a wrong assumption about starting temperature, the apparent agreement would evaporate and the honest range would be much wider. An overlap driven by a single indicator is not really corroboration at all.
Common mistakes
- Understating individual ranges to force a narrow overlap. This manufactures false precision.
- Treating an overlap driven by one indicator as corroborated. Check which range sets each bound.
- Combining methods that share an assumption. They are not independent.
- Dismissing an empty overlap. It is evidence that something is wrong.
- Applying indicators outside their reliable window. Each has a period where it says little.
Frequently asked questions
What are rigor and livor mortis?
Rigor mortis is the stiffening of muscle after death as ATP is depleted, typically beginning within a few hours, becoming complete over several more, and passing off after a day or so. Livor mortis is the settling of blood under gravity, producing discolouration that becomes fixed after a similar period. Both are temperature-dependent and both give broad ranges rather than precise times.
Which indicator is most reliable?
It depends entirely on the interval and the conditions. Temperature is most informative in the first several hours and useless after a day or two. Rigor and livor cover a similar early window. Gastric contents can help where a last meal is known. Entomology takes over for longer intervals and can be informative over weeks. There is no general ranking.
What does an empty overlap mean?
That at least one estimate is wrong, or that the ranges were derived under incompatible assumptions — for example a temperature estimate assuming a stable ambient when the body had been moved. It is a signal to re-examine the inputs, not to widen a range until something fits.
Why not just average the estimates?
Because averaging assumes the estimates are measurements of the same quantity with random error, which they are not. They are constraints derived from different physical processes, each with its own systematic assumptions. Taking the intersection respects that; averaging would produce a figure no individual method supports.
Is what I enter stored?
No. Ranges are processed entirely in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — Forensic Science Regulator guidance on evaluative opinion and expert evidence
- National Institute for Health and Care Excellence — clinical guidance relevant to post-mortem examination
Sources are checked at publication and can change — how I choose and check references.