By Zencalcy Editorial TeamLast reviewed About us
The shock index is a simple ratio of heart rate to systolic blood pressure. It rises when the heart compensates for reduced effective circulating volume, often before blood pressure itself falls. This calculator divides heart rate by systolic pressure and flags values that sit outside the usual resting range.
Heart rate divided by systolic blood pressure.
Shock index = HR ÷ SBP
A resting shock index of roughly 0.5–0.7 is typical. A value of 0.9 or more is often used as a concerning threshold, and 1.0 or more is described as high. The index is a screening signal, not a diagnosis: pain, anxiety, fever, medicines and pregnancy can all raise heart rate independently of perfusion.
| Symbol | Meaning |
|---|---|
| HR | Heart rate in beats per minute. |
| SBP | Systolic blood pressure in mmHg. |
| Shock index | The ratio of heart rate to systolic pressure. |
For 80 bpm and 120 mmHg, the index is 80 ÷ 120 = 0.67, within the usual resting range. For 110 bpm and 100 mmHg, it is 110 ÷ 100 = 1.10, which is high. A rate of 90 bpm at 100 mmHg gives 0.90, the point at which concern is commonly raised.
Blood pressure is the product of cardiac output and vascular resistance, and the body can defend it through several mechanisms. One of the earliest is a rise in heart rate. That is why a patient can have a normal systolic reading while becoming haemodynamically stressed. The shock index makes that compensation visible by putting heart rate in the numerator. Its simplicity is also its weakness: it cannot tell why the rate is high or why the pressure is low. A young athlete may have a resting index near 0.5, while an older person on a beta-blocker may have a misleadingly low value during bleeding. Serial trends are more informative than a single number, and the index should always be read alongside skin perfusion, mental status and urine output.
Continue with the Mean Arterial Pressure Calculator, Pulse Pressure Calculator, or the QTc Calculator — or browse more cardiology tools and all health calculators.
Around 0.5 to 0.7 is commonly cited for resting adults. Values below that can occur in trained athletes or with slow heart rates, and values above it can occur with pain, fever or anxiety without any circulatory problem.
Blood pressure, ECG and risk scores are screening aids, not diagnoses. A single reading can be misleading; trends and proper technique matter. Scores estimate population risk and do not replace clinical assessment, anticoagulation decisions or emergency care.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026