The first big career choice you make can haunt you for years

It can be awkward to ask for more money from your employer, especially when you start a new job.

"That one last conversation - where you negotiate salary - can unnerve even the most savvy job seeker," 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."

But chickening out of a salary negotiation, especially at the beginning of your career, could haunt you forever.

"Many job candidates don't know what to ask for and end up leaving money on the table. You don't have to be one of them," Taylor says. "You'd be well served in your career to become comfortable with the process. You get one chance to accept a final compensation package at your company, so be prepared to make a persuasive argument."

Negotiating your starting salary - and continuing to negotiate every few years or when you start a new job - could make a $1 million difference in your lifetime earnings.

In the chart above, we compare the earnings of two hypothetical employees, Alex and Taylor. Alex accepts a company's initial salary offer of $45,000 and gets a 1% raise each year.

Taylor negotiates for $5,000 more at the outset for a starting salary of $50,000, gets a 1% raise each year, and negotiates a 4% raise every three years.

By the time they've reached retirement age, Taylor is making $121,370 a year, while Alex is earning $70,416. Over the course of their careers, Taylor has earned $1.06 million more than Alex.

The key to earning more money may be switching jobs, according to an analysis from financial services company Nomura. Employees who changed jobs earned about 1% more year-over-year than those who stayed with the same employer.

Job switchers likely experience stronger bargaining power and greater salary increases when more opportunities are available or they find a new higher-paid role that better matches their talents, according to the report.

But it's still possible to earn more at your current job. Switching departments, for example, could land you in a role that pays significantly more.

Ultimately, the comparison here proves that the importance of securing big salary gains in your 20s and 30s can't be overlooked.

Here's to a successful negotiation.