One way to answer is "I'm looking for $X." If they ask for your current salary, you then say "I'm looking for $X." However, this only really matters if you're

One way to answer is "I'm looking for $X." If they ask for your current salary, you then say "I'm looking for $X." However, this only really matters if you're applying for a job at a salary much higher than your current salary. If you're currently earning $X and you're looking for $X plus 10%-20%, it doesn't matter much. If you already have a job, and they lowball you on salary negotiations, walk away and keep your current job.