It pays to keep your mouth shut.

Many employers are dying to know one thing: How much you make at your current job. About 43% of job seekers say that they were asked that question during the interview process, according to a survey of more than 15,000 job hunters released Tuesday by compensation data and software firm PayScale.

In most cases, it’s perfectly legal to ask that question (though New York City, Philadelphia and Massachusetts recently passed legislation barring it.) And many people just go ahead and answer it. The Payscale survey found that just 23% of job seekers refused to say how much they were currently paid when an interviewer inquired about it.

But it’s often a big mistake to answer that question, career experts say — at least if you want to get a fat raise with the new job. “No one needs to know what you make currently,” says Cynthia Pong, a career coach at Embrace Change Consulting. “The only reason employers ask this is so that they can low-ball you when they make you an offer and keep you in the same salary bracket. Resist!”

If you’re asked the question early in the interview process, career coach Roy Cohen says you can buy some time by saying something like “I was expecting that you would need to know either my compensation history or my expectations. I’m happy to provide that information, but hopefully we can hold off for the time being.” Then ask more about the position so they start talking about the role itself and you can show them you’re a perfect fit. “You create a competitive advantage [that can help you then get paid more] when you demonstrate with passion and conviction that your skills and experience are a perfect match,” says Cohen — and that takes time to do.

Even if you do that, it’s likely that the salary question will rear its head later. In that case, turn the question around on them to make it about what you want to get paid at the new company, rather than what you get paid now. Say something like “according to my salary research, the going rate for someone with my background is between $X and $Y. I would be comfortable with negotiating a salary within that range,” says Cheryl Palmer, founder of Call to Career.

In many cases, this will do the trick and you won’t have to disclose your salary. But, says, Cohen, “if they insist, give it up,” as you “can always negotiate when an offer is extended.”

And leadership consultant Nancy Halpern points out that if you do end up telling them your salary, you need to have an explanation for why your current salary is so different from your desired one. For example, if you’re coming from a lower salary, explain why with examples why this is — like maybe you began your career in a bad economy so you took what you could get, or you have now gotten more experience and education so you deserve more, says New York City-based Career Coach Carlota Zimmerman.