π°οΈ Postmortem Interval Estimator
Forensic timing from temperature and body changes.
Estimated hours since death (Glaister)
For informational purposes only, not medical advice.
The Glaister equation estimates hours since death from body cooling: (98.6 minus rectal temperature in Fahrenheit) divided by 1.5. A rectal temperature of 90 F gives (98.6 - 90) / 1.5, about 5.7 hours. Rigor mortis and livor mortis add independent timelines: rigor begins in 2 to 6 hours and resolves by 24 to 36, while lividity fixes around 8 to 12 hours. Forensic pathologists triangulate all three, never trusting one alone.
This is educational forensic science, the kind taught in criminal justice and medicolegal courses. Real death investigation belongs to medical examiners with thermometers, scene data, and training no web page provides.
How to Use This Estimator
Enter the rectal temperature and the observed stages of rigor and livor mortis. The tool computes the Glaister estimate and shows each method's implied window.
Enter the rectal (core) temperature in Fahrenheit, ideally taken with ambient temperature noted.
Select the rigor mortis stage: beginning, fully developed, or passing.
Select the livor mortis stage: blanching or fixed. Compare the three windows for consistency.
The Three Clocks
Algor mortis is the cooling clock: bodies lose roughly 1.5 F per hour early on, slowing as they approach ambient. Rigor mortis is the chemical clock: ATP depletion locks muscle fibers, starting in small muscles and spreading, then releasing as decomposition begins. Livor mortis is the gravity clock: blood settles to dependent areas, blanching under pressure until clotting fixes it in place.
When the clocks agree, confidence rises; when they disagree, something modified one of them, heavy clothing slowing cooling, or movement after lividity fixed, and the discrepancy itself becomes evidence.
Worked Example
Rectal temperature 90 F: (98.6 - 90) / 1.5 = 5.7 hours by Glaister. Rigor is fully developed, suggesting 8 to 12 hours; lividity blanches, suggesting under 8 to 12. The three windows overlap around 6 to 10 hours, a reasonably tight estimate for field methods.
Now change one input: same temperature but fixed lividity. Fixed livor says beyond 8 to 12 hours while cooling says about 6, a disagreement pointing at slowed cooling, perhaps heavy blankets or a warm room. The pathologist would weight the scene accordingly.
Reading Your Result
| Finding | Implied window |
|---|---|
| Warm body, no rigor, no lividity | Under ~2 hours. |
| Cooling, rigor developing, blanching lividity | Roughly 2 to 8 hours. |
| Full rigor, fixed lividity | Roughly 8 to 24 hours. |
| Rigor passing, decomposition signs | Beyond 24 to 36 hours; entomology takes over. |
My take: the most useful output is the disagreement case. Matching clocks confirm; mismatched clocks investigate. That principle, trust but triangulate, is the whole of field forensic timing.
Limits
Cooling rate depends on ambient temperature, clothing, body size, air movement, and surfaces, none of which this page sees; the 1.5 F rate is a rough average, not a constant. Fever or hypothermia before death shifts the starting point. Beyond about a day, insect activity and decomposition outpace these methods. This is classroom material, and any real case needs the medical examiner.
Related Tools
Body size affects cooling rates, so the BMI calculator frames the mass variable. For the living, the BMR calculator covers the heat production these equations run in reverse.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
How is time of death estimated?
Forensic pathologists combine body cooling (algor mortis), rigor mortis, livor mortis, and later, decomposition and insect activity, interpreted against scene conditions. No single method stands alone.
What is the Glaister equation?
Hours since death = (98.6 - rectal temperature in F) / 1.5. It assumes roughly 1.5 F of cooling per hour from a normal starting temperature, a useful field approximation with wide error bars.
What is rigor mortis?
Postmortem muscle stiffening from ATP depletion, beginning 2-6 hours after death in small muscles, fully developed around 12 hours, and resolving over 24-36 hours as decomposition breaks down muscle.
What is livor mortis?
Postmortem blood settling to dependent body areas, appearing within 30 minutes to 2 hours and becoming fixed (non-blanching) around 8-12 hours. Fixed lividity also shows whether a body was moved.
What is algor mortis?
The postmortem cooling of the body toward ambient temperature, fastest in the first hours. Rectal temperature is the standard field measurement for the Glaister estimate.
How accurate are these estimates?
Rough: individual methods carry multi-hour uncertainties, worse with unknown ambient conditions. Triangulating all three narrows the window; precision beyond that needs laboratory methods.
What affects body cooling rate?
Ambient temperature, clothing and coverings, body size and fat, air movement, wetness, and surfaces. A clothed body indoors cools far slower than the 1.5 F/hour average assumes.
What happens after 24-36 hours?
Rigor resolves and the early clocks expire; forensic entomology (insect development) and decomposition staging take over for longer intervals, requiring specialist analysis.
Can these methods be used on a real case?
Only by qualified death investigators. This page teaches the concepts for education; real determinations need the medical examiner with proper measurements and scene investigation.
Why does lividity show if a body was moved?
Because fixed lividity stays where gravity put it. Lividity on the back of a body found face-down means it was moved after about 8-12 hours, a classic forensic observation.