When negotiating salary for a position with a new company, or within a promotion process at your current employer, your current salary can be a serious liability. ESPECIALLY if you're underpaid.
Whenever possible, try to avoid discussing your next salary in the context of your current one. However, it's important to do some homework before this conversation to put yourself in an offensive position in case you are asked for the number.
Calculate your total compensation with your current employer. That includes salary, 401K contributions, insurance premium paid by your employer, the value of your vacation time, etc.
If you are directly asked for your salary, you can at least give a higher number by saying "my total compensation package with [employer] is worth about $100,000" and then redirect the conversation by transitioning to the upcoming opportunity.
For example, "My total compensation package with [employer] is worth about $100,000, and I expect my salary in this position to be around $110,000 given the skills I'll bring and the expected outcomes for the position. How does $110,000 relate to the salary [employer] expects to pay for this role?"
Notice when the term "compensation" and when the term "salary" is used. Be sure not to call your calculated compensation your current salary, or else you'd be seriously fudging the numbers. You don't want to be caught in an awkward lie and risk having the conversation go south.