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PERC Calculator

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Apply the PERC rule for low pretest probability chest pain patients to check whether pulmonary embolism can reasonably be excluded without further testing.

Reviewed by the thecalcu.com team · Last updated July 18, 2026

Only valid for patients already assessed by a clinician as low pretest probability for PE. The PERC rule is not a general pulmonary embolism screening tool — it must not be applied to patients with moderate or high pretest probability.

Age ≥50

Heart Rate ≥100 bpm

O2 Saturation <95% on Room Air

Prior DVT or PE

Recent Trauma or Surgery (≤4 Weeks)

Hemoptysis

Exogenous Estrogen Use

Unilateral Leg Swelling

Criteria Met

0/ 8

PERC Result

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Not a substitute for clinical judgment. The PERC rule is only meant to be applied by a clinician who has already determined the patient has a low pretest probability of PE — it must never be used alone to rule out pulmonary embolism or guide care.

What is a PERC Rule?

The PERC Calculator applies the Pulmonary Embolism Rule-out Criteria (PERC), a set of eight clinical criteria used only in patients a clinician has already determined to have a low pretest probability of pulmonary embolism (PE), to check whether PE can reasonably be excluded without further testing. If none of the eight criteria are present, the patient is "PERC negative"; if any criterion is present, PERC does not rule out PE and further workup is needed.

Select yes or no for each criterion below to see your total and PERC result. For a related VTE risk tool used in a different clinical context, see the Padua Score Calculator; for a related emergency chest pain risk tool, see the HEART Score Calculator.

Why Use a PERC Calculator?

Checking eight criteria by hand under emergency department time pressure is where small omissions happen. This calculator walks through each criterion clearly and shows the PERC result instantly, along with which criteria contributed to a positive result.

It's useful for emergency medicine clinicians and trainees reviewing the PERC criteria structure, and for anyone wanting to understand the terminology used during a pulmonary embolism workup discussion.

Who Should Use This Calculator?

Emergency medicine, internal medicine, and pulmonology clinicians and trainees can use this tool to check the PERC criteria against a specific patient scenario, always within the required low pretest probability context. Students studying pulmonary embolism diagnostic pathways can use it to understand how the eight PERC criteria are structured and applied.

This calculator is strictly for informational and educational purposes and is not a substitute for a clinician's judgment. The PERC rule only applies within a low pretest probability context already established by a qualified clinician, it is not a general screening tool, must never be used by patients to self-diagnose, and must never delay seeking emergency care for concerning symptoms like sudden shortness of breath or chest pain.

What Insights Does the PERC Calculator Give You?

Criteria Met is the primary result, how many of the eight PERC criteria are present, out of a possible 8.

PERC Result translates that count into a plain-language PERC negative or PERC positive classification, reflecting the original validation study's all-or-nothing rule structure, any single criterion present makes the rule PERC positive.

How to use this PERC Rule calculator

  1. Confirm the patient has already been assessed by a clinician as low pretest probability for PE, the PERC rule does not apply otherwise.
  2. Select Yes or No for Age ≥50.
  3. Select Yes or No for Heart Rate ≥100 bpm.
  4. Select Yes or No for O2 Saturation <95% on Room Air.
  5. Select Yes or No for Prior DVT or PE.
  6. Select Yes or No for Recent Trauma or Surgery (≤4 Weeks), Hemoptysis, Exogenous Estrogen Use, and Unilateral Leg Swelling.
  7. Review the Criteria Met count and PERC Result, and ensure this is applied within the appropriate clinical context by a qualified provider.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The PERC rule checks eight binary criteria:

- Age ≥50
- Heart rate ≥100 bpm
- O2 saturation <95% on room air
- Prior DVT or PE
- Recent trauma or surgery (≤4 weeks)
- Hemoptysis
- Exogenous estrogen use
- Unilateral leg swelling

If zero criteria are present, the patient is PERC negative (PE reasonably excluded without further testing, in a low pretest probability patient). If any criterion is present, the patient is PERC positive (PERC does not rule out PE; further workup needed).

Worked example: A 42-year-old patient already assessed as low pretest probability for PE, with a heart rate of 88 bpm, oxygen saturation of 98% on room air, and none of the other seven criteria present, is PERC negative, all 8 criteria are absent, so PE can reasonably be excluded without further testing in this low-risk context, per the original Kline et al. 2004 (Journal of Thrombosis and Haemostasis) validation study.

Frequently Asked Questions

What does the PERC rule do?
The PERC (Pulmonary Embolism Rule-out Criteria) rule is a set of eight clinical criteria used, in a patient a clinician has already assessed as low pretest probability for pulmonary embolism (PE), to determine whether PE can reasonably be excluded without further testing. If none of the eight criteria are present, the patient is 'PERC negative' and further PE-specific testing may reasonably be avoided in that low-risk context.
Who can this rule be applied to?
The PERC rule applies only to patients a clinician has already judged to have a low pretest probability of pulmonary embolism using their overall clinical gestalt or a validated pretest probability tool. It is explicitly not a general screening test and must never be applied to patients with moderate or high pretest probability for PE.
What happens if all eight criteria are 'no'?
If all eight criteria are absent, the patient is considered 'PERC negative,' meaning that in this specific low-pretest-probability population, the risk of missing a clinically significant PE is low enough that further testing (such as D-dimer or CT pulmonary angiography) may reasonably be avoided. This decision still rests with the treating clinician.
What happens if even one criterion is present?
If any single criterion is present, the patient is 'PERC positive,' meaning the rule does not rule out PE, and the clinician should proceed with further PE-specific workup, typically starting with a D-dimer test or other diagnostic path based on the full clinical picture.
Why does age 50 count as a criterion?
Age is one of several factors that increases baseline risk of venous thromboembolism, and the PERC rule uses a straightforward age cutoff of 50 as one of its eight component criteria. Even a single positive criterion is enough to make the rule PERC positive, regardless of how mild it seems on its own.
What does 'exogenous estrogen use' mean?
Exogenous estrogen use refers to taking estrogen-containing medications, such as combined oral contraceptives or hormone replacement therapy, which are well-established as increasing venous thromboembolism risk. This is distinct from naturally occurring estrogen produced by the body.
Can this calculator rule out pulmonary embolism on its own?
This calculator is for informational and educational purposes only and simply applies the published PERC criteria to the answers you provide. It is only valid within a low pretest probability context already established by a clinician, and it must never be used by patients to self-diagnose or rule out pulmonary embolism without medical evaluation.
How was the PERC rule developed?
The PERC rule was derived and validated by Kline JA, et al. and published in the Journal of Thrombosis and Haemostasis, 2004;2(8):1247-1255, then further validated in subsequent multicenter studies. It's designed to help reduce unnecessary CT scans and radiation exposure in low-risk emergency department patients.
Is PERC the same as a D-dimer test?
No, PERC is a clinical criteria checklist applied before any blood test, used to decide whether D-dimer testing is even necessary in a low-risk patient. If a patient is PERC positive, or if PERC doesn't apply because pretest probability isn't low, a D-dimer test or imaging is typically the next diagnostic step.
How does this relate to the HEART Score Calculator in this same tool set?
The [HEART Score Calculator](/heart-score-calculator/) addresses chest pain concerning for acute coronary syndrome, while the PERC rule addresses a different diagnostic question, ruling out pulmonary embolism in a low pretest probability patient. Both may be relevant tools depending on how a patient's chest pain or shortness of breath presents.
Is VTE risk assessment the same during hospitalization as with PERC?
No, the [Padua Score Calculator](/padua-score-calculator/) assesses VTE risk proactively in hospitalized medical patients without current PE symptoms, to decide on preventive anticoagulation, while PERC is applied to patients presenting with symptoms who are being worked up for possible acute PE. They serve different clinical purposes.
What should I do if I'm worried about a blood clot?
Seek prompt medical evaluation rather than trying to self-assess using this or any other online tool, symptoms like sudden shortness of breath, chest pain, or leg swelling should always be evaluated by a healthcare professional, who can determine pretest probability and apply the appropriate diagnostic pathway.
Also known as
PERC rule calculatorpulmonary embolism rule-out calculatorPE rule-out criteria calculatorlow probability PE calculatorPERC score calculator