Information is power in a negotiation. The best way to make sure that you are getting paid what you are worth is by performing market research. Why? Without data, women tend to underestimate the value of their work and ask for less.
For instance, there was a study where men and women were asked to pay themselves in a private situation what they thought was fair pay for a fixed amount of work. Without any guidance, men paid themselves 63% more on average than women. When researchers put a list of names and amounts that others had been paid, women and men didn’t have a significant gap in how much they suggested they should get paid. So what does this mean? Women don’t value their work as inferior, we just have a difficulty accurately assessing value of our work without external reference points.
Glassdoor, PayScale, Angelist, Ladders, Buffer, and Robert half are all websites where you can search for compensation data.