Any salesperson will tell you the downside of the “unlimited potential” of commission-based compensation: The unlimited potential for your personal income to plummet when business or seasonal cycles head south.

But salespeople often have trouble facing this music. “The number one person that salespeople must sell is themselves,” says John Sestina, president of a financial planning firm in Columbus, Ohio. “They tend to be optimistic, and that’s their problem. They don’t focus on where they are now, their current position.”

Believing that flush times will likely bring on more of the same, many salespeople are already picturing how they’ll spend the entire commission check as they sign it on the back. “The biggest thing is burning through the dollars and not investing them,” says Drew Stevens, a sales consultant in St. Louis.

How can salespeople consistently avoid going into debt during lean times -- and even save for the future, as all of us are supposed to? By taking an honest look at their current personal finances, making a rational plan for the future and sticking to it.

Assess Your Current Cash Flow

According to financial planners and seasoned sales professionals, the first step toward stabilizing your finances is to create an objective picture of them.

“Do a cash-flow projection, which shows ups and downs by month,” Sestina says. “Keep this on a spreadsheet or Quicken, and record your sales and expenses there. The cash-flow sheet has a positive influence because it’s a goal sheet. When salespeople put it down in writing, they usually meet their goals; it’s a psychological thing.”

Developing a useful projection means spending time tracking actual outlays and being sure not to omit anything substantial. “I give them a spreadsheet and ask them to itemize monthly expenses,” Stevens says. “Lots of folks haven’t even done that.”

A consultation with an accountant can assure you that you’re creating a financial analysis sufficient to serve as the foundation for a sound plan.

Create a Financial Plan, Not a Fantasy

The next step is to create a spending and savings plan that will enable you to cover current expenses and save for a house down payment, retirement and other major goals while weathering the downs and ups of life on commission.

“When your income is sporadic, consider making two budgets, one with your accustomed level of spending, and one no-frills baseline budget,” says Sally Herigstad, a CPA and author of Help! I Can’t Pay My Bills. “When the money comes in more slowly than expected, you can cut back to the baseline budget and know you’ll make it.”

Some experts suggest saving a set percentage of each commission check, regardless of whether you’re having a good quarter. To do that, you’ll need a buffer of perhaps several months’ expenses in your spending account to get you through the lows.

Get External Support for Your Plan

Very few of us are consistent enough savers to make such a plan work without outside help. So it pays to save through an automated transaction, whether direct deposit or a transfer to a savings, investment or retirement account.

“With each check, set aside a predetermined percentage based on your budget, for savings and investment,” says Brad Stroh, co-CEO of Bills.com in San Mateo, California. “Some financial institutions let you arrange automatic transfers from your checking account to a savings account.”

But don’t count on anyone else to oversee your financial arrangements -- including tax liabilities, which often catch salespeople unawares.

“In my second year as a sales rep, I made great strides but failed to realize that my employer was deducting based on the tax withholding rate of my previous year’s income [which was significantly lower]", says Corey Donovan, vice president of business development at Vibrant Technologies in Minnetonka, Minnesota. “I was shocked to find that I owed several thousand dollars come April 15.”

Look at the Larger Picture

Alas, setting a steady course for your finances and sales career doesn’t ensure success. “If even your baseline budget exceeds your average income over a period, it’s time to make some hard decisions,” Herigstad says.

All your determined planning and disciplined action may ultimately lead you to target a more lucrative sales position or industry. “Sometimes people realize the potential isn’t there in their current job for what they want to do financially, so they look for a new job,” Sestina says.