How Much Does A Private Polygraph Test Cost?

A private polygraph can be an investigative tool for a defense lawyer, but it is not proof that a person is truthful. California Evidence Code 351.1 generally excludes results, examiner opinions and references to taking or offering the test in criminal proceedings unless all parties stipulate. Speak with counsel before hiring an examiner, paying for a test or sharing results.

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.

How much does a private polygraph test cost?

Fees vary by examiner, location, duration, the questions to be tested and whether a written report or later testimony is included. This page does not quote a firm price. Ask for a written estimate and identify any separate charge for rescheduling, additional testing, travel or testimony.

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?

Evidence Code 351.1 applies to criminal proceedings, including pretrial and postconviction hearings, and juvenile criminal-offense proceedings. It excludes results, examiner opinions and references to an offer, refusal or taking the test unless all parties stipulate. The statute does not itself exclude otherwise admissible statements made during the examination. Civil admissibility is a separate analysis.

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?

A favorable result does not automatically establish innocence or require dismissal. Counsel may evaluate whether to use a privately arranged examination in negotiations, but any potential disclosure must be weighed against the evidentiary and strategic risks.

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 evaluation: an unfavorable or inconclusive result is not a substitute for reviewing the actual evidence, available defenses and sentencing consequences. No plea should be selected solely because of a polygraph outcome.

How should you prepare for a polygraph test?

Preparation should follow counsel’s and the examiner’s directions. These steps can reduce avoidable problems but do not guarantee accuracy:

• 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.

Do not assume a private result or interview is automatically privileged or immune from discovery. Counsel should assess who retained the examiner, the purpose of the work, any stipulation and applicable disclosure obligations before the examination. Statements made during a test may create a separate evidentiary issue.

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.

Robert M. Helfend has practiced criminal defense since 1984. His State Bar record confirms his active license, and his Super Lawyers profile lists selection for 2020 through 2023.

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

Published February 5, 2025.

What should the lawyer and examiner agree on first?

Question	Why it matters
What is the test intended to answer?	A narrow, legally relevant issue should be identified; a broad claim of innocence can obscure the disputed facts.
Who retains the examiner and receives the report?	The engagement and disclosure plan affect confidentiality, work-product analysis and later use.
What is included in the price?	The interview, examination, report, recordings, follow-up and testimony may be priced separately.
What happens with an inconclusive result?	Discuss whether further work has value and whether any result will be disclosed before testing begins.

A lawyer should compare any proposed examination with the records that can answer the underlying allegation directly, such as messages, location evidence, witnesses or forensic findings.

Sources and legal standards

• Evidence Code 351.1

Legal information checked October 10, 2026. The charge, evidence and applicable version of the law control the analysis of an individual case.

References

1. California Evidence Code § 351.1. https://leginfo.legislature.ca.gov/faces/codes_displayText.xhtml?lawCode=EVID&division=3.&title=&part=&chapter=4.&article=1.
2. 29 C.F.R. § 801.4. https://www.law.cornell.edu/cfr/text/29/801.4