About the Tylenol Overdose Calculator
This calculator applies the Rumack-Matthew nomogram, the standard clinical tool for estimating the risk of liver injury after a single, acute acetaminophen (Tylenol) overdose. It compares a measured serum acetaminophen concentration against a time-based treatment-line threshold, and separately reports the ingested dose per kilogram of body weight.
How the treatment line is calculated
The treatment line assumes first-order elimination with an apparent half-life of about 4 hours. It is anchored at 150 mcg/mL at 4 hours after ingestion and is calculated as:
Threshold (mcg/mL) = 150 x 0.5^((hours since ingestion - 4) / 4)
At 4 hours the threshold is 150 mcg/mL; by 24 hours it has fallen to roughly 4.7 mcg/mL. A measured level at or above the threshold for the corresponding time is read as probable risk of hepatotoxicity; a level below it is read as low risk from that ingestion. The historical 200 mcg/mL "possible toxicity" line sits above this 150 mcg/mL "treatment" line, which already builds in roughly a 25% margin of safety and is the line most commonly used to decide on treatment.
Why the 4-to-24-hour window matters
The nomogram applies only to a single, acute ingestion at a known time, and only to levels drawn 4 to 24 hours after that ingestion. Before 4 hours, absorption may not be complete and the level can still be rising, so an early level cannot be plotted on the line - the standard approach is to redraw at 4 hours. After 24 hours, or for staggered and chronic ingestions, the nomogram is not validated, and treatment decisions rely on clinical assessment, liver function tests, and toxicology consultation instead.
The dose-per-weight check
When a reported dose is available, dividing it by body weight gives a rough milligrams-per-kilogram figure. Reported acute ingestions at or above roughly 150 to 200 mg/kg (or above about 7.5 to 10 g in an adult) have traditionally been used as a trigger to obtain a 4-hour level, even before that level is known.
When to consult a professional
This tool performs nomogram arithmetic only; it does not diagnose overdose, does not replace a blood test, and does not direct treatment. Any suspected acetaminophen overdose is a medical emergency - contact Poison Control or emergency services immediately rather than relying on a calculator.