A lot of people have a fantasy tough that once you sell one novel you will live a life of relative luxury. You will sleep until noon, do three or four hours of work, and then relax in your hot tub or head out to a party. After all J.K. Rowling only has to put out a less than a book a year and she's one of the richest women in the UK.
But she's the exception. The sad fact is that many pros often can't make a living at writing alone. If they do often theirs is the second income and their spouse has a “real job” with benefits and retirement plans. Often they moonlight as a professional writer and make the bulk of their money doing something else like teaching. The stats are better for writers than for actors but they still aren't very encouraging.
Don't count on that huge advance on your first sell to fund your fantasy. One statistic I've heard mentioned at convention panels is that the average advance on a first novel is $5000. I happened to stumble on the source for that information the other day.
Buckell had input from nearly a hundred published authors when he did his calculations and that's a statistically sound sample size.
Think about your current gross pay. Add an amount equal to your employer's contributions to your retirement plan and your insurance coverage. Divide that by $5000. That's how many publication ready novels you would need to write and sell in a single year when you're first starting out to make your living at writing and maintain your current standard of living, assuming that your advances stayed about the same for a year or so
Now, if your books sell well you can expect a raise in your future advances, and of course there can be royalties beyond the advance, a bestseller really can fund you for years, but you can also end up having to repay part of the advance if the book doesn't sell as well as the publisher hoped. Film rights can add thousands of dollars to the total too, but producers don't take submissions from authors, THEY will come to YOU if they happen to read your book and think it would make a good movie. Anything beyond the advance is a chancy thing so best to be prepared for a worst case (no bestseller, no big increase for a while) scenario in the event of your best case (you sell several novels or the equivalent) outcome.
Short stories and non-fiction articles vary by market as to what they will bring but I did the math once with per word rates in front of me and figured out that on average a page of finished work brings in about the same no matter what the medium. Reprint rights on shorter works, if marketed well, can be more profitable than royalties on books but again that's future return, not what you can get right away.
So, lets say you need $30,000 a year just to give a solid round number. You would need to turn out six novels or a novel every two months. Given how cautious publishers are about saturating the market with too many books by the same author you can see why many midlist authors work under several pen names.
Can you write a finished novel or it's equivalent, including time to do research and multiple drafts, in two months? Can you write one in six weeks if that's what you need to meet the bills? Once you become known it may not get much better. Many of my favorite authors regularly do four books a year even after developing a fanbase. Can you maintain that output? Can your spouse earn enough to make up the difference between what you can produce and what you need to survive?
If not then don't quit your day job.
And don't make snide comments about “hacks” who care about what will sell instead of obsessing about making an artistic statement. They are the ones who produce most of the real enduring art anyway. People like Shakespeare and Twain managed to create work that had both popular appeal and artistic merit but without commercial success they wouldn't have produced the body of work that they did.
The great thing about writing is that you don't have to quit your job and go to school to get a special degree and hope that someone will hire you once you're done. You can work at it nights and weekends until you start selling enough to justify a switch to full time. You don't even have to do it for money if you don't want to.
If you do, it's best to look at the financial reality first and plan for it just like you would with any career chan