14 signs that you're underpaid

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Feeling like you might be underpaid can be one of the most disheartening aspects of work.

"It stands to reason, because for many, compensation is a concrete litmus test of how well you're performing and progressing on the job — and how highly you're valued," says Lynn Taylor, a national workplace expert and the author of "Tame Your Terrible Office Tyrant: How to Manage Childish Boss Behavior and Thrive in Your Job."

According to a 2014 survey from Glassdoor.com, a whopping 39% of employees believed that they were not receiving fair pay in their current job.

But it's hard for them to be sure.

"The topic of employees' salaries is well guarded by most companies, so it's not always easy to figure out how your pay compares to your colleagues'," says Taylor. "If you're willing to invest the time and research or look for the signs, however, you'll be better informed as to whether you should ask for a raise or walk."

Here are 14 signs you're paid less than you should be:

A similar job listing on your company website offers higher pay

"If there are multiple positions like yours at the company, the job description closely resembles yours, and the salary is higher, that's one of the most obvious signs," says Taylor.

Stay on top of this by searching your own company's job postings every now and then to monitor what new employees are being paid, "and to see if that feels reasonable given your current level of experience and role in the company," adds Michael Kerr, an international business speaker and author of "The Humor Advantage."

Your firm's revenue has taken off, but your salary has barely budged

If your company is private, it's harder to measure revenue growth vs. a public company.

"But you're likely having discussions about corporate growth with managers in your normal course of business," Taylor says. "This is an opportunity to dig deeper. If you're armed with the fact that the firm has seen 20% growth in one year, but your salary is under par, you'll strengthen your argument for a raise."

Research tells you you're underpaid

This is a pretty solid sign.

"You must stay on top of the current salaries for your type of position," Taylor says. "There are many online sources for this, including PayScale.com, Glassdoor.com, Indeed.com and Salary.com."

Kerr says using an online salary calculator to see where average wages are or should be, for someone in your role and with your level of education and years of experience, can be a good starting point and may indicate if there's a discrepancy between your wage and the going rate.