Are you considering a private polygraph test and wondering how much it costs or whether it could help your criminal case?

In this guide, we’ll answer some common questions about private polygraph tests in California, from pricing to legal admissibility.

If you’re thinking about using a polygraph as part of your defense strategy, it’s very important to understand its implications. Always consult with your attorney.

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How much does a private polygraph test cost?

A private polygraph test typically costs between $500 and $2,500, depending on factors such as location, duration, examiner expertise, and whether a formal report is required.

Some providers charge by the hour, while others offer flat-rate pricing. It’s crucial to research examiners, verify their credentials, and ensure they use accepted testing methodologies.

Is a polygraph test a “Lie detector”?

Polygraph tests are commonly referred to as “lie detector tests.” They measure physiological responses such as heart rate, blood pressure, respiration, and skin conductivity while the subject answers a series of questions.

The underlying theory is that deceptive answers cause measurable physiological changes.

However, polygraph accuracy remains a topic of debate, with concerns about false positives and negatives. While government agencies use them for investigations and employment screenings, their reliability is not universally accepted in the scientific or legal community.

What is a private polygraph test?

A private polygraph test is conducted by an independent examiner rather than a government agency. In legal defense, private polygraph tests may be used to support a defendant’s claims, challenge accusations, or assess credibility. Attorneys may also use them to identify weaknesses in a case before trial.

Are polygraph test results admissible in California courts?

Generally, polygraph results are not admissible in California criminal or civil trials due to concerns over their reliability. However, if both the prosecution and defense mutually agree to admit the results, they may be considered as evidence.

Even though courts do not accept polygraph tests as definitive proof of truth or deception, they can still influence negotiations, plea bargains, or settlement discussions.

Can a polygraph test be used as exculpatory evidence?

Because polygraph results are not considered completely reliable, they cannot be used as direct exculpatory evidence. However, in some cases, they may be used strategically during pre-trial negotiations to persuade prosecutors to reconsider charges.

How can a private polygraph test help your defense?

If your attorney believes it could be beneficial, voluntarily taking a private polygraph test may serve several strategic purposes:

Credibility Assessment – A passed polygraph could help support your credibility in discussions with prosecutors or investigators.
Pre-Trial Preparation – Attorneys may use polygraph tests internally to identify weaknesses in a case and better prepare for cross-examination.
Plea Bargain Consideration – If a defendant fails a private polygraph, it may be a signal to consider negotiating a plea deal rather than proceeding to trial.

How should you prepare for a polygraph test?

Proper preparation can help ensure accurate results. Consider the following:

Get adequate rest before the test.
Answer all questions truthfully.
Inform the examiner about any medical conditions or medications that could affect physiological responses.
Discuss the implications with your attorney beforehand.

What happens if you ‘fail’ a polygraph test?

A failed polygraph does not necessarily mean someone is lying. Nervousness, medical conditions, medications, or examiner errors can all impact results. This is one reason courts do not consider polygraph tests conclusive evidence.

If you fail a private polygraph, your defense team is not obligated to disclose the results. However, if the test is shared during negotiations, it could affect how prosecutors or opposing parties perceive your credibility.

Contact the Helfend Law Group today

A strong legal defense requires a strategic approach, and while a private polygraph test may be a useful tool, it is only one piece of the puzzle. Legal defense strategies should be comprehensive, evidence-based, and tailored to your specific case.

At Helfend Law Group, we stay informed on the latest legal developments to build the most effective defense for our clients. Since 1984, Robert M. Helfend has defended individuals facing criminal charges, helping thousands achieve favorable outcomes. He has been recognized by Lead Counsel, Super Lawyers, and the National Trial Lawyers Top 100.

For a free case review, call 800-834-6434 today.

Published February 5, 2025.