Some safe tax harbors tougher to navigate
The safe harbor is a little choppier, however, if you make a lot of money.

If your previous year's adjusted gross income was more than $150,000 (for married couples filing jointly and single taxpayers; $75,000 for married taxpayers filing separately), and you want to base your estimated tax payment on the prior year's amount, you'll have a higher safe-harbor percentage to meet.

For 2009 estimated payments, the safe-harbor target for a high-earning taxpayer is 110 percent of the filer's 2008 tax bill. That means if your adjusted gross income on that previous return was $150,000 and you ended up with a $30,000 tax bill, the IRS expects you to pay $33,000 -- $30,000 plus 10 percent -- in 2009 via estimated and withholding taxes to guarantee you don't encounter additional IRS charges in penalties and interest.

"With both in a couple earning or people holding multiple jobs, the salary cap is not as out of reach as it may seem, especially if they had a good investment or sold a piece of investment property during the year, too," says Durand.

Stimulus changes to safe harbor
Small businesses were given a bit of a break in connection with the safe-harbor numbers, thanks to the American Recovery and Reinvestment stimulus bill signed into law on Feb. 17.

For 2009, individuals who get most of their income from a small business don't have to make estimated payments based on 100 percent of their 2008 returns to avoid penalties and interest. Instead, the new law allows these filers to pay 90 percent of the prior year's taxes.

To qualify for this lower safe harbor, your adjusted gross income must be less than $500,000; you must employ, on average, 500 or fewer workers at your business; and you must be able to show that more than 50 percent of your gross income on your prior year's return was from your small business.

"Most small-business owners pay tax on their businesses through their own personal tax returns, so this could help," says Barbara Weltman, attorney and author of J.K. Lasser's "Small Business Taxes 2009."

Paying only when you earn
A large estimated tax bill can take a big bite out of even a wealthier earner's wallet, despite being spread out in four payments.

There is, however, a way to postpone, if not avoid, the tax pain.

Although the IRS will always take your money early, you don't have to make estimated tax payments until you have income on which you will owe the tax.

If most of your untaxed income comes in one quarter (like stock dividends paid at year's end), or you operate a business where income fluctuates throughout the year, you should consider paying your estimated taxes under the annualized income system.

"The annualized method allows you to take a look at each quarter independently and pay the tax in the quarter that you earned it," says Durand. "Say your job is one where most income is in the summer, such as landscaping, rather than the winter; you want to pay the taxes when you have the money."

With this approach, your required estimated tax payment for one or more periods may be less than the amount figured using the four-equal-payments method. To find that out, you'll have to complete a work sheet, found in IRS Publication 505, Tax Withholding and Estimated Tax. Sole proprietors need an additional work sheet found in IRS Publication 505 to determine annualized self-employment taxes that are included with the estimated payments.

And you'll need to file Form 2210 with your annual return to explain why you didn't send in the expected equal payments, says Durand. This will keep the IRS, which assumes you earned the money equally during the year, from charging you an underpayment penalty and interest for not paying enough in a particular filing quarter.

"It is a little more complicated," Durand says. "But for cash flow, it's better and it puts the tax in the quarter when it is earned."

A way to avoid estimated filing
Does the prospect of struggling through work sheets and filing even more tax returns make your head spin? There is an alternative.

If you have wage income in addition to untaxed earnings, file a new W-4 at work and ask your boss to start taking out more payroll taxes to cover any shortfall. This strategy also works for couples who file jointly but where only one spouse has wage income subject to withholding.

Your take-home pay will be a bit lighter, but you'll be off the hook for estimated tax payments.

Freelance writer Kay Bell writes Bankrate's tax stories from her Austin, Texas, home. She also writes two tax blogs, Eye on the IRS for Bankrate and Don't Mess With Taxes, and is the author of the book "The Truth About Paying Fewer Taxes."