Estimate time since death using Henssge nomogram body cooling model. Factors in body temperature, ambient temperature, weight, clothing, body build, and environment with postmortem changes timeline.
Estimating the time since death — the postmortem interval (PMI) — is one of the most critical tasks in forensic pathology and medicolegal death investigation. The most reliable early method is algor mortis: the cooling of the body after death. The Henssge nomogram, the gold standard since the 1980s, models this cooling using a double-exponential equation that accounts for an initial temperature plateau (the "sigma phenomenon") followed by progressive cooling toward ambient temperature.
This calculator implements a simplified Henssge-based model incorporating seven corrective factors: rectal core temperature, ambient temperature, body weight, clothing/covering, body build (fat insulation), body surface (conductive vs. insulating), and the double-exponential cooling curve. It provides a point estimate with a ±15% confidence interval, which is consistent with published Henssge nomogram accuracy of ±2.8 hours for the 95% confidence interval in the first 24 hours.
Beyond temperature-based estimation, the tool includes a comprehensive postmortem changes timeline correlating rigor mortis, livor mortis, corneal changes, and early decomposition signs with estimated hours since death — enabling multi-modal PMI assessment as forensic pathologists use in practice.
Accurate PMI estimation is central to medicolegal death investigation — it establishes timelines, corroborates or refutes witness statements, and narrows suspect windows. While forensic pathologists use complex nomograms and multi-modal assessment, this calculator provides an accessible implementation of the Henssge model for forensic science education, scene investigators, and preliminary estimation.
Henssge double-exponential: Q = (T_rectal − T_ambient) / (37.2 − T_ambient) = 1.25 × e^(-kt) − 0.25 × e^(-5kt) Cooling constant k = 1.2815 / (corrective_factor) Corrective factor = clothing × mass_factor × build_adj × surface_adj Solved iteratively for time t (hours)
Result: Estimated PMI: ~8.5 hours (range 7.2–9.8 h)
Body cooling from 37.2°C to 30°C in a 20°C environment with standard correction factor ~1.0 yields a temperature ratio Q of 0.59. Solving the double-exponential equation gives approximately 8.5 hours postmortem, with a ±15% confidence interval of 7.2 to 9.8 hours.
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The Henssge nomogram achieves ±2.8 hours accuracy (95% CI) within the first 24 hours postmortem under standard conditions. Accuracy decreases after 24 hours as the body approaches ambient temperature. Environmental variables (wind, rain, heating) reduce accuracy further.
Rectal temperature most closely reflects core body temperature, which is the basis of the Henssge model. Brain (tympanic) or hepatic temperatures can be used but have different cooling curves. Rectal temperature is the standard in forensic practice and is the temperature the nomogram was validated with.
After death, body temperature remains relatively stable for 30-90 minutes before linear cooling begins. This "sigma phenomenon" is due to residual metabolic heat, thermal inertia, and ongoing enzymatic reactions. The double-exponential model accounts for this plateau; simple Newton's law does not.
Yes. The model assumes a starting body temperature of 37.2°C. If the person had a fever (39-40°C), the PMI will be underestimated. Similarly, hypothermia before death overestimates PMI. Adjusting the baseline temperature improves accuracy when antemortem temperature is known.
Bodies in water cool approximately twice as fast as in air at the same temperature. The water correction factor (0.5) partially accounts for this, but accuracy in aquatic environments is reduced compared to indoor scenes. Current, water temperature variability, and clothing significantly affect cooling.
Forensic pathologists use multiple modalities: rigor mortis progression (2-12 hours onset, 24-36 hours resolution), livor mortis fixation (8-12 hours), vitreous potassium concentration, gastric contents analysis, entomological evidence (insect activity), and scene investigation findings. Use this as a practical reminder before finalizing the result.