Salary
Average Salary: $45,000
Expected Lifetime Earnings: $1,878,660
Who knows, really? The Bureau of Labor Statistics estimates a syndicated cartoonist makes between $30,000-$80,000 per year, but in reality, the amount varies tremendously (source).
For one thing, that's just syndication money, meaning income from newspapers. We can safely assume licensed Peanuts, The Far Side, and Dilbert merchandise brought their respective creators a couple (truckloads) of bucks from time to time. Who hasn't seen a The Far Side coffee mug, or "A Charlie Brown Christmas," or a Dilbert tear-away yearly calendar?
Not long after Dilbert became a runaway success, Adams wrote that his "newfound prosperity" was starting to alienate him from his friends a bit. Truthfully, it was probably his new habit of never leaving his house that was alienating him, but the point is, his success resulted in a pretty nice influx of new cash.
However, don't reserve the Maserati just yet. Remember that cartoonists are looking for syndication, meaning newspapers pay for the privilege of running your cartoon. You're paid a percentage of what each newspaper forks out to have your cartoon grace their pages. More papers printing your stuff equals more money.
If 1,000 papers buy your strip, you're probably doing really, really well, at least before taxes. If 100 papers buy it, you probably won't have any trouble paying the bills, but you may need to think Ford rather than Lexus. If no one buys your strip, well...McDonald's is almost always hiring.
Like most careers, you should probably expect a slow start. You may get rejected several times before someone agrees to buy your strip. And from there, you might still see a slow spread in syndication.
The good news is, as more newspapers carry your strip, more people will see it. As more people see it and it gains popularity, more newspapers will in turn want to carry it. It's kind of like a snowball: the bigger it gets, the faster it gets bigger.