If you worry that you might not pick up on your boyfriend's dishonesty, you may be right: According to "Psychology Today" magazine, people are only between 40 and 65 percent accurate when it comes to recognizing that someone isn't telling them the truth. Learning how to tell whether a boyfriend is lying requires you to be alert to nonverbal cues and to be willing to face the consequences if you learn that he has been dishonest.
Choose a time that's conducive to conversation. Don't pick the five minutes before you have to leave for work or an evening when he's come home exhausted from the office. Try to choose a time when you're both comfortable and relaxed.
Sit so that you can see his face and body language clearly. If he's sitting at a table, move your chair out from the table so that you can see his body. If you're sitting beside each other, move so that you can see his face and body.
Ask a casual question that your boyfriend has no reason to lie about, such as where he'd like to have dinner that weekend or what time a sporting event is supposed to take place. Pay attention to his face and body language so that you know what his "normal" response to questions is.
Plan your question carefully. Ask the precise question you want answered, and avoid being vague. For instance, if you want to know whether your boyfriend went to a strip club with his friends last week when he said he was working late, ask him that and not whether he ever goes to strip clubs.
Look directly at your boyfriend, and ask your question. Resist the urge to elaborate on what you've said: Ask, and then let him respond.
Watch for physical cues, such as crossing his legs, folding his arms, touching his face or looking very intently at your eyes. These all may be signs that he's not telling the truth, according to Gay and Kathlyn Hendricks of the Hendricks Institute in an article for Pregnancy.org.
Listen for audio cues, such as changes in the pitch of his voice, coughing or clearing his throat or a sudden increase in his speaking speed. According to the Hendricks Institute, these audio cues can signal a lie.
Notice attitude changes, such as hostility or anger, that your boyfriend uses to deflect attention from your question. For instance, if you ask whether he was at a strip club, and he says, "I'm offended that you're even asking me that" instead of answering your question, he could be trying to distract you from his dishonesty.
Determine whether your boyfriend is telling the truth by using a combination of these clues. The more simple and straightforward his responses, the more likely it is that he's being honest.